Physics Nobel 2008: Spontaneous Broken Symmetry

Yoichiro Nambu

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2008 with one half to Yoichiro Nambu, Enrico Fermi Institute, University of Chicago, IL, USA "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics" and the other half jointly to Makoto Kobayashi, High Energy Accelerator Research Organization (KEK), Tsukuba, Japan and Toshihide Maskawa, Yukawa Institute for Theoretical Physics (YITP), Kyoto University, Japan "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature"

The fact that our world does not behave perfectly symmetrically is due to deviations from symmetry at the microscopic level. As early as 1960, Yoichiro Nambu formulated his mathematical description of spontaneous broken symmetry in elementary particle physics. Spontaneous broken symmetry conceals nature’s order under an apparently jumbled surface. It has proved to be extremely useful, and Nambu’s theories permeate the Standard Model of elementary particle physics. The Model unifies the smallest building blocks of all matter and three of nature’s four forces in one single theory.

Makoto Kobayashi

The spontaneous broken symmetries that Nambu studied, differ from the broken symmetries described by Makoto Kobayashi and Toshihide Maskawa. These spontaneous occurrences seem to have existed in nature since the very beginning of the universe and came as a complete surprise when they first appeared in particle experiments in 1964. It is only in recent years that scientists have come to fully confirm the explanations that Kobayashi and Maskawa made in 1972. It is for this work that they are now awarded the Nobel Prize in Physics.

They explained broken symmetry within the framework of the Standard Model, but required that the Model be extended to three families of quarks. These predicted, hypothetical new quarks have recently appeared in physics experiments. As late as 2001, the two particle detectors BaBar at Stanford, USA and Belle at Tsukuba, Japan, both detected broken symmetries independently of each other. The results were exactly as Kobayashi and Maskawa had predicted almost three decades earlier.

Toshihide Maskawa

A hitherto unexplained broken symmetry of the same kind lies behind the very origin of the cosmos in the Big Bang some 13.7 billion years ago. If equal amounts of matter and antimatter were created, they ought to have annihilated each other. But this did not happen, there was a tiny deviation of one extra particle of matter for every 10 billion antimatter particles. It is this broken symmetry that seems to have caused our cosmos to survive.

The question of how this exactly happened still remains unanswered. Physicists are now searching for the spontaneous broken symmetry, the Higgs mechanism, which gave the particles their masses and there should be a Higgs particle, theory predicts. Scientists at the world's most powerful particle accelerator, the Large Hadron Collider at the European Organization for Nuclear Research or CERN in Switzerland, will be looking for this particle when they re-start the collider in spring of 2009.

High Energy Physics: 5 Needed Breakthroughs -- Michael Dine

[Professor Michael Dine of the University of California at Santa Cruz is today's guest in our ongoing feature '5 Breakthroughs'. He is also a faculty member at the university's Santa Cruz Institute for Particle Physics (SCIPP).

In his long career spanning about 3 decades (He got his PhD from Yale University in 1978), Prof. Dine made major contributions in the areas of supersymmetry, string theory, and other efforts to develop a "new physics" beyond the standard model of particle physics.

He has been one of the principal contributors (with various collaborators) to the set of ideas associated with supersymmetry, and was among the first to propose that supersymmetry might well be broken at these energy scales. Prof. Dine developed some of the first potentially realistic models of supersymmetry phenomenology, and was among the first to explore the dynamics of supersymmetric theories, uncovering an array of surprising phenomena, some of potential relevance to experiments, and others of interest to mathematicians and more theoretically minded physicists. In recent years, he developed a proposal for the phenomenology of supersymmetry which has become a standard for both theoretical and experimental analyses. Currently, he is engaged in a number of projects exploring the experimental possibilities for the Large Hadron Collider (LHC).

Prof. Dine also made significant contributions in superstring theory. Most of his work has been motivated by the hope of making specific predictions from the theory for accelerators, but in the course of these efforts, he made several important contributions to the overall theoretical structure. Much of his current effort is involved with trying to understand whether one can make predictions from this theory relevant to the Large Hadron Collider (LHC). At the moment, he believes there is a promising (but not certain), approach, based on a popular set of ideas commonly referred to as the `landscape'.

In December, 2007 issue of 'Physics Today', Prof. Dine provided an excellent account of the relationship between string theory and particle experiments in an article entitled "String Theory in the era of the Large Hadron Collider" (p.33, Article Link).

He also authored a widely acclaimed book on this topic: "Supersymmetry and String Theory: Beyond the Standard Model" (Cambridge University, 2007).

In the field of cosmology, he made significant contributions to the theory of inflation, and to ideas about the dark energy and dark matter. Simultaneously with others, he proposed the axion as a dark matter candidate, which has remained, over the years, one of the two most plausible possibilities (the other arising in supersymmetric theories). He also proposed one of the most widely studied ideas for understanding the origin of the matter-antimatter asymmetry (known as the Affleck-Dine mechanism) explaining why there was not, initially, an equal amount of matter and antimatter, which could have simply annihilated each other.

It's our pleasure to present this list of 5 most important breakthroughs that Prof. Dine would like to see in the physics of elementary particles.
-- 2Physics.com ]

Five needed breakthroughs in elementary particle physics

1) Determination of the origin of electroweak symmetry breaking – the masses of the W and Z bosons, quarks and leptons. Is it a single Higgs field (particle), as in the simplest version of the standard model? Or is it associated with supersymmetry, large or warped extra dimensions, or something else? This question should be settled over the next three to five years by the Large Hadron Collider at CERN, due to be commissioned late this year.

2) Identifying the dark matter. There are several plausible, well-motivated candidates coming from particle physics: the lightest supersymmetric particle (LSP), the axion (a hypothetical particle seemingly required to understand features of the strong nuclear force), and others. There are ongoing, dedicated searches for both the LSP and the axion. If the LHC discovers supersymmetry, there is a good chance we will discover the dark matter particle in underground experiments, and we will be able to study in some detail how this particle was produced at the earliest stages of the big bang. The axion searches also have a real chance of finding something, if the axion is the dark matter, though detectors with a broader reach may be necessary.

3) Theoretically, one urgent question is: does string theory predict that supersymmetry, warping, or something else is responsible for electroweak symmetry breaking? Can we settle this question theoretically before the LHC? Can we make more detailed predictions? Recent developments associated with the string landscape suggest this might be possible, but the problem is challenging.

4) There are many problems of quark and lepton flavor (the occurrence of several types of quarks and leptons, and the puzzling features of their masses and couplings) which we would like to understand. What is the scale of baryon number violation? What can we understand, theoretically and experimentally, about the origin of neutrino mass? Can we develop a compelling theory, which explains the very different features of the charged fermion masses and those of the neutrinos? Can we establish experimentally the nature of the neutrino masses? Can we decide that leptogenesis, and not, say, coherent effects associated with supersymmetry, are responsible for the asymmetry between matter and antimatter in the universe?

5) Theoretically and experimentally, what more can we learn about inflation, the period of rapid expansion in the very early universe for which there is growing observational evidence, as well as strong theoretical arguments? At a microscopic level, we are far from understanding how inflation comes about. All existing models have troubling features. Can we get beyond this situation? Can supersymmetry or string theory help? If we have improved theories, they will be subject to some experimental tests; how far can we go?

High Energy Physics : 5 Needed Breakthroughs -- Mark Wise

[In the ongoing feature '5 Breakthroughs', our guest today is Mark Wise, the John A. McCone Professor of High Energy Physics at California Institute of Technology.

Prof. Wise is a fellow of the American Physical Society, and member of the American Academy of Arts and Sciences and the National Academy of Sciences. He was a fellow of the Alfred P. Sloan Foundation from 1984 to 1987.

Although Prof. Wise has done some research in cosmology and nuclear physics, his interests are primarily in theoretical elementary particle physics. Much of his research has focused on the nature and implications of the symmetries of the strong and weak interactions. He is best known for his role in the development of heavy quark effective theory (HQET), a mathematical formalism that has allowed physicists to make predictions about otherwise intractable problems in the theory of the strong nuclear interactions.

To provide a background of his current research activities, Prof. Wise said,"Currently we have a theory for the strong, weak and electromagnetic interactions of elementary particles that has been extensively tested in experiments. It is usually called the standard model. Even with this theory many features of the data are not explained. For example, the quark and lepton masses are free parameters in the standard model and are not predicted. Furthermore the theory has some unattractive aspects -- the most noteworthy of them being the extreme fine tuning needed to keep the Higgs mass small compared to the ultraviolet cutoff for the theory. This is sometimes called the hierarchy problem."

He explained,"My own research breaks into two parts. One part is using the standard model to predict experimental observables. Just because you have a theory doesn’t mean it’s straightforward to use it to compare with experiment. Usually such comparisons involve expansions in some small quantity. One area I have done considerable research on is the development of methods to make predictions for the properties of hadrons that contain a single heavy quark".

He elaborated,"The other part is research on physics that is beyond what is in the standard model. In particular I have worked on the development of several extensions of the standard model that solve the hierarchy problem: low energy supersymmetry, the Randall-Sundrum model and most recently the Lee-Wick standard model. This work is very speculative. It is possible that none of the extensions of the standard model discussed in the scientific literature are realized in nature."

Prof. Wise shared the 2001 Sakurai Prize for Theoretical Particle Physics with Nathan Isgur and Mikhail Voloshin. The citation mentioned his work on "the construction of the heavy quark mass expansion and the discovery of the heavy quark symmetry in quantum chromodynamics, which led to a quantitative theory of the decays of c and b flavored hadrons."

He obtained his PhD from Stanford University in 1980. While doing his thesis work, he also co-authored the book 'From Physical Concept to Mathematical Structure: an Introduction to Theoretical Physics' (U. Toronto Press, 1980) with Prof Lynn Trainor of the University of Toronto (where he did his B.S. in 1976 and M.S. in 1977). He also coauthored, with Aneesh Manohar, a monograph on 'Heavy Quark Physics' (Cambridge Univ Press, 2000).

We are pleased to present the list of 5 needed breakthroughs that Prof. Mark Wise would be happy to see in the field of high energy physics.
-- 2Physics.com]

"Here go five breakthroughs that would be great to see:

1) An understanding of the mechanism that breaks the weak interaction symmetry giving the W's and Z's mass. This we should know the answer to in my lifetime since it will be studied at the LHC (Large Hadron Collider) and I am trying to stay healthy.

2) Reconciling gravity with quantum mechanics. Currently the favored candidate for a quantum theory of gravity is String Theory. However, there is no evidence from experiment that this is the correct theory. Perhaps quantum mechanics itself gives way to a more fundamental theory at extremely short distances.

3) An answer to the question, why is the value of the cosmological constant so small? I am assuming here that dark energy is a cosmological constant. (Hey if it looks like a duck and quacks like a duck it's probably a duck.) A cosmological constant is a very simple term in the effective low energy Lagrangian for General Relativity. The weird thing about dark energy is not what it is but rather why it's so small.

4) An understanding of why the scale at which the weak symmetry is broken is so small compared to the scale at which quantum effects in gravity become strong. This is usually called the hierarchy problem. Breakthrough (1) might provide the solution to the hierarchy problem or it might not.

5) Discovery of the particle that makes up the dark matter of the universe and the measurement of its properties (e.g., spin, mass, ...).

There are other things I would love to know. For example, is there a way to explain the values of the quark and lepton masses? But you asked for five."

High Energy Physics: 5 Needed Breakthroughs -- Pierre Ramond

Pierre Ramond [photo courtesy: University of Florida, Gainesville]

[ Prof. Pierre Ramond, Distinguished Professor of Physics at University of Florida in Gainesville, is today's guest in our ongoing feature '5-Breakthroughs'.

During his long career starting with the PhD work at Syracuse University in 1969, Prof. Ramond contributed in some significant developments in the study of elementary particles and fields. Notable among those is the crucial role he played in the early development of superstring theory.

Early string theory proposed by Yoichiro Nambu and others in 1970 was based on bosonic string. At that point, Pierre Ramond took the crucial step of generalizing the Virasoro algebra, the symmetry algebra of the bosonic string, to a superconformal algebra including anticommuting operators. The inclusion of a fermionic string to accompany the bosonic ones completed the theory of strings. In 1971, he generalized Dirac's equation for point-like particles to string-like ones, which laid a solid foundation for the superstring theory. A comprehensive list of the variety of work he did can be found in Google Scholar link.

Prof. Ramond is a Fellow of American Physical Society and American Academy of Arts & Sciences. In August 2004, he was awarded Oskar Klein Medal by Swedish Royal Academy of Sciences and Stockholm University.

Many of us grew up with his celebrated book "Field Theory: A Modern Primer" (Addison / Wesley, 1981) and also experienced the pleasure of "Journeys Beyond the Standard Model"(Perseus, 1999), his other book. It's thus our pleasure to present the 5 most important breakthroughs that Prof. Ramond would like to see in High Energy Physics.
-- 2Physics.com Team]

Here is my list of five:

Finding Supersymmetry with the Large Hadronic Collider, and if found, understanding Supersymmetry breaking.

Understanding why there are three chiral families of Elementary Particles (closely related to finding the organizing principle behind chiral symmetry breaking, e.g. Yukawa interactions).

Observation of Proton Decay in the Laboratory.

Determining the Character (Majorana or Dirac) of Neutrino masses.

Identifying Dark Matter.

"Changing Constants, Dark Energy and the Absorption of 21 cm Radiation" -- By Ben Wandelt

Ben Wandelt [Photo credit: Department of Physics, University of Illinois/Thompson-McClellan Photography]

Rishi Khatri and Ben Wandelt have recently proposed a new technique for testing the constancy of the fine structure constant across cosmic time scales using what may prove to be the ultimate astronomical resource for fundamental physics. In this invited article, Ben Wandelt explains the motivation for this work and the physical origin of this treasure trove of information.

Author: Ben Wandelt
Affiliation: Center for Theoretical Astrophysics, University of Illinois at Urbana-Champaign

What makes Constants of Nature so special? From a theorist's perspective constants are necessary evils that ought to be overcome. The Standard Model has 19 “fundamental constants,” and that is ignoring the non-zero neutrino masses which bring the total count to a whopping 25. That's 25 numbers that need to be measured as input for the theory. A major motivating factor in the search of a fundamental theory beyond the Standard Model is to explain the values of these constants in terms of some underlying but as yet unseen structure.

What's more, not even the constancy of Constants of Nature (CoNs) is guaranteed (Uzan 2003). Maybe the quantities we think of as constants are actually dynamic but vary slowly enough that we haven't noticed. Or even if constant in time, these numbers may be varying across cosmic distances.

Quite contrary to taking the constancy of the CoNs for granted, one can argue that it is actually surprising. String theorists tell us these constants are related to the properties of the space spanned by the additional, small dimensions beyond our observed four (3 space + 1 time). These properties could well be dynamical (after all, we have known since Hubble that the 3 large dimensions are growing) so why aren't the 'constants' changing? This perspective places the onus on us to justify why the small sizes are at least approximately constant. So the modern, 21st century viewpoint is that it would be much more natural if the CoNs were not constant but varying—either spatially or with time.

By way of example consider the cosmic density of dark energy. The 20th century view was in terms of “vacuum energy,” a property of empty space that is predicted by the Standard Model of particle physics. This is qualitatively compelling, but quantitatively catastrophically wrong. More recently three main categories of attempts emerged to explain that particular constant (and ignore the vacuum energy problem). The first category explains dark energy as some new and exotic form of matter. The second category of explanations sees the acceleration of the Universe as evidence that our understanding of Gravity is incomplete.

The third argues that the dark energy density is just another CoN, the “cosmological constant,” which appears as an additive term in Einstein's equations of general relativity and therefore increases the rate of the expansion of the Universe. This possibility was originally suggested by Einstein himself. While this is quite an economical way of modeling all currently observed effects of the universal acceleration it is also hugely unsatisfactory as an actual explanation—somewhat analogous to a boss explaining the size of your salary as “Because that's the number and that's it.” The attempt to turn this into an actual explanation through the pseudo-anthropic reasoning associated with string-theoretic landscape arguments corresponds to your boss adding “Because if you wanted to earn any more than that you wouldn't be here to ask me this question.”

If we consider the cosmic density of dark energy as another CoN that appears in Einstein's equation, it should also somehow arise from the underlying fundamental theory, like the other constants. By the identical argument we went through before we should in fact be surprised by its constancy. Hence most of the theoretical activity takes place within categories one and two, endowing this supposedly constant CoN with dynamical properties that can in principle be tested by observation.

Of course none of these aesthetic or theoretical arguments for what constitutes a satisfying explanation holds any water if it cannot be tested. And in fact, there are two sorts of tests: laboratory tests and astronomical observations. For definiteness, let's focus the discussion on a particular CoN, the most accurately measured CoN, the fine structure constant α. This number tells us the strength of the force that will act on an electric charge when it is placed in an electromagnetic field. If you have heard about the charge of the electron you have already encountered this constant in a slightly different form. Since charge has units (Coulomb), one could always redefine the units to change the value. So the relevant number is a dimensionless combination of the charge of the electron with other CoNs. This gives α ≈ 1/137.

Over the years, the value of α has been measured in laboratory experiments to about 10 digits of accuracy. Using the extreme precision of atomic fountains, the value of α was measured over 5 years and found to have changed by less than 1 part in 10¹⁵ per year [Marion et al. 2003].

Laboratory experiments do have their distinct advantages: the setup is under complete control and repeatable. However, they suffer from the very short lever arm of human time scales. Astronomical observations provide a much longer lever arm in time. The best current observations use quasar absorption lines and limit the variation to a similar accuracy when put in terms of yearly variation—but these measurements constrain variation over the last 12 billion years, the time it took the Universe to expand by a factor of 2.

In fact, using such quasar data, one group has claimed a detection of a change in α of 0.001% over the last 12 billion years [Webb et al. 2001]—though this claim is certainly controversial [Chand et al. 2006], but things may become interesting at that level.

My graduate student Rishi Khatri and I have discovered a new astronomical probe of the fine structure constant that is likely the ultimate astronomical resource of information for probing its time variation. Compared to the quasar data our technique probes α at an even earlier epoch, only a few million years after the Big Bang, when the Universe went from 200 times smaller to 30 times smaller than it is today. And in principle, if some technological hurdles can be overcome, there is enough information to measure α to nine digits of accuracy 13.7 billion years in the past! This would be 10,000 more sensitive than the best laboratory measurements.

What is this treasure trove of information? It arrives at the Earth in the form of long wavelength radio waves between 6 meters and 42 meters long. Theses radio waves started out their lives between 0.5 cm and 3 cm long, as part of the cosmic microwave background that was emitted when the hot plasma of the early Universe transformed into neutral hydrogen gas. As the Universe expands, these waves stretch proportionally. After about 7 million years, the ones with the longest initial wavelength first stretch to a magic wavelength: 21 cm. At this wavelength these waves resonate with hydrogen atoms: they have just the right energy to be absorbed by its electron. Waves that are absorbed are removed from the cosmic microwave background and can be seen as an absorption line (similar to the well-known Fraunhofer lines in the solar spectrum). As the Universe expands during the next 120 million years, waves that were initially shorter stretch to 21 cm and are similarly absorbed by hydrogen. After this time, light from the first stars heat the hydrogen to the point that it can no longer absorb these waves [Loeb and Zaldarriaga 2004]

It turns out that the amount of absorption is extremely sensitive to the value of α. Therefore, the spectrum of absorption lines we expect to see in the radio waves is an accurate record of the value of α during this epoch. We could even look for variations of α within this epoch, and check for spatial variations of α and other 'constants.' I argued above that these variations are expected on general grounds, but they are also predicted by specific string-theory inspired models for dark energy such as the chameleon model.

The tests we propose are uniquely promising to constrain fundamental physics models with astronomical observations. Important technological hurdles have to be overcome to realize measurements of the radio wave spectrum at the required level of accuracy. Still, the next time you see snow on your analog TV you might consider that some of what you see is due to long wavelength radio waves have reached you from the early Universe, having traveled to you across the gulf of cosmic time and carry in them the signature that may reveal the fundamental theory of Nature.

References
Chand H. et al. 2006, Astron. Astrophys. 451, 45.
Khatri, R. and Wandelt, B. D. 2007, Physical Review Letters 98, 111301. Abstract
Loeb, A. and Zaldarriaga, M. 2004, Physical Review Letters 92, 211301. Abstract
Marion, H. et al. 2003, Phys.Rev.Lett. 90, 150801. Abstract
Uzan, J.-P. 2003, Reviews of Modern Physics, vol. 75, 403. Abstract
Webb,J. K. et al. 2001, Physical Review Letters 87, 091301. Abstract

Superstring Theory: 5 Needed Breakthroughs -- John H. Schwarz

John H. Schwarz (photo credit: Patricia Schwarz)

[In 2001, Prof. John Preskill of Caltech wrote a poem "To John Schwarz" (full text here) which started as ..

"Thirty years ago or more
John saw what physics had in store.
He had a vision of a string
And focused on that one big thing."

The name 'Schwarz' is intimately associated with the origin and evolution of Superstring theory. In 1971 John Schwarz and André Neveu developed an early version of superstring theory, which led among other things to the discovery of supersymmetry. In 1974 Joël Scherk and he proposed that string theory should be used to construct a unified quantum theory containing gravitation.

In 1984 Michael Green and he discovered an anomaly cancellation mechanism, which resulted in string theory becoming one of the hottest areas in theoretical physics. As Prof. Preskill's poem describes:

If you weren't there you couldn't know
The impact of that mightly blow:
"The Green-Schwarz theory could be true ---
It works for S-O-thirty-two!"

John Schwarz is the Harold Brown Professor of Theoretical Physics at California Institute of Technology (Caltech) where he taught and conducted research since 1972. He received the Dirac Medal of the International Centre for Theoretical Physics, Trieste in 1989, as well as the Dannie Heineman Prize for Mathematical Physics of the American Physical Society in 2002. He was a fellow of the MacArthur Foundation in 1987 and in 1997 he was elected to the National Academy of Sciences.

Prof. Schwarz coauthored a new string theory textbook entitled `String Theory and M-Theory: A Modern Introduction,' which was published earlier this year by Cambridge University Press.

We can't resist ending this note quoting again from John Preskill's poem:

Because he never would give in,
Pursued his dream with discipline,
John Schwarz has been a hero to me.
So please, don't spell it with a "t"!

Ladies and Gentlemen, it's our honor and privilege to share with you the excitement of superstring theory by presenting this list of 5 breakthroughs that John Schwarz would like to see.
-- 2Physics.com Team]

5 most important breakthroughs that I would like to see in
SUPERSTRING THEORY
by John H. Schwarz

(1) Discovery of supersymmetry at the Large Hadron Collider (LHC):

Supersymmetry is an intrinsic feature of superstring theory, and therefore I am convinced that it exists at a fundamental level. The big question is whether it is broken at a sufficiently low energy (the TeV scale) that supersymmetry partner particles can be discovered at the LHC. There are several well-known arguments for why this is likely. Discovery of supersymmetry would not prove that superstring theory is the correct fundamental theory and nondiscovery would not prove that it is wrong. Still, if it is discovered, string theory would deserve credit for spawning the study of supersymmetry in the first place.

The experimental discovery of superpartner particles (and hence supersymmetry)would be very exciting for several reasons: It would set the agenda for experimental particle physics for decades to come ensuring the vitality of high-energy physics research. It would be enormously informative, leading eventually to the formulation of a "supersymmetric standard model'' extending the current standard model to much higher energies. Such a supersymmetric standard model would provide a much better target for string theorists to try to relate to Planck scale physics, where string theory is most directly applicable, by "top-down reasoning". String theorists would like to predict all of this in advance, of course,but that does not seem to be possible.

(2) Other experimental evidence for string theory:

Aside from supersymmetry, there are a number of other possible experimental signals for string theory that have been considered, and there may be others that nobody has thought of yet. In my opinion, all of the following are unlikely to be observed, because the Planck scale (the natural energy scale of quantum gravity) is so far beyond what is experimentally accessible. However, there are scenarios in which quantum gravity phenomena can extend to much lower energies, and thereby possibly become observable, which certainly are worth exploring. The methodologies for making such a discovery fall into two broad categories: astronomical/cosmological observations and accelerator experiments. The first category can look for cosmic strings, primordial gravity waves, and certain subtle features of the cosmic microwave background. Accelerators, such as the LHC, can look for signals indicating the presence of extra dimensions, black holes, gravitons, or fundamental strings.

(3) More fundamental formulation of string theory/M-theory; emergent spacetime :

The current understanding of string theory is based on perturbation theory expansions of various symmetrical limits supplemented by a beautiful web of conjectured duality relations. What is missing is a single complete formulation of the theory that accounts for these various symmetrical limits and dualities. Such a formulation is likely to implement some deep principle that has not yet been recognized. It is also likely to be completely unique without any adjustable parameters or other features that can be altered.

There are various reasons to believe that the existence of space and time is not something built into the theory itself, but rather emerges as a property of certain classes of solutions. If this is correct, the theory will be radically different from any previous physical theory all of which describe what happens in a given spacetime. Even Einstein's theory of gravity (the general theory of relativity), in which the geometry of spacetime is determined dynamically,assumes the prior existence of a spacetime manifold.

(4) Determine whether time is emergent and clarify the status of quantum mechanics:

The previous item suggested that space and time are emergent properties of solutions to string theory rather than intrinsic features of the underlying theory. There is considerable evidence for the emergence of spatial dimensions in various settings, but there is no compelling evidence for the emergence of time. Experience with relativity makes it hard to imagine that space and time could be radically different in this regard. On the other hand, the notion of time is central in quantum mechanics, which is formulated as unitary time evolution. If time is emergent, some extension of the rules of quantum mechanics would seem to be required. The consistency of string theory requires that quantum mechanics is exactly correct. I am not questioning that this will continue to be the case in the future, only that quantum mechanics may need to be generalized somewhat to extend its domain of applicability.

(5) Determine the correct solution of the theory:

A unique equation can have many different solutions. By the same token, string theory can describe a rich variety of physical realities. We are still in the early stages of mapping out the possibilities, but the indications are that the number of possibilities is enormous. The picture that has been proposed, whose validity is not completely evident, is that there is an energy function that is a complicated function of many variables (called moduli) and that each of the minima of this function corresponds to a different solution of the theory. Assuming its validity, this picture raises a lot of questions: How is the "correct'' solution (i.e., the one that describes the Universe that we observe) determined? Is it a cosmological accident or is there some other principle? How can we determine the correct solution? How much empirical information needs to be input in order to determine it uniquely and make everything else computable (in principle)? These types of questions are very important to explore. They are stimulating a lot of serious research, as well as some spirited debate that is even spilling over into the public domain.

High Energy Physics : 5 Needed Breakthroughs -- Guenakh Mitselmakher

[ Our guest today in the ongoing feature,
'5-Breakthroughs' is Guenakh Mitselmakher, Distinguished Professor of Physics and Director of the Institute for High Energy Physics and Astrophysics at University of Florida, Gainesville.

Currently, he is also the leader of the Muon system development for the CMS detector. CMS is one of two major universal detectors at the Large Hadron Collider at CERN, Geneva, Switzerland, which will begin operations in 2007-2008. He is also a member of the LIGO Science Collaboration, looking for the so called "burst" signals of Gravitational Wave (signals of limited duration), which may originate at a variety of astrophysical sources like supernova explosion.

In the long career starting from his PhD work in 1974 at the Joint Institute for Nuclear Research, Dubna, Russia, Prof. Mitselmakher made numerous important contributions in the field of Experimental high energy physics. Notable among those are studies of the lepton number conservation in rare decays of muons, investigations of the electromagnetic structure of pions, including the first measurements of the pion charge radius and polarizability, studies of the Standard Model and Beyond with the DELPHI detector at CERN and with the CDF detector at Fermilab. He also proposed a new type of Particle detectors (what is now called Quantum Calorimetry or bolometry), now broadly used in Paricle Physics and Astrophysics.

Here are 5 important breakthroughs that Prof. Mitselmakher would like to see in High Energy Physics.
-- 2Physics.com Team]

1. To understand the origin of "Dark Energy".

2. To understand the origin of "Dark Matter".

3. To find the Higgs or an alternative explanation for the spontaneous symmetry breaking in the Standard Model.

4. To explain (and calculate) the parameters of the Standard Model, such as masses and mixing angles of quarks and leptons.

5. To test if quarks (and other particles considered to be point-like) have a substructure.

Quantum Theory : 5 Needed Breakthroughs -- Stephen Adler

Stephen Adler with grandchild in 2004 (photo courtesy: Institute for Advanced Study, Princeton)

[Prof. Stephen Adler of the School of Natural Sciences at the Institute of Advanced Study, Princeton is a widely respected authority in the field of Quantum Theory.

During the long career starting with Ph.D work in 1964 from Princeton University, Prof. Adler
continued to make important contribution in the field of Elementary Particles, Quantum Field Theory and Foundation of Quantum Physics.
His recent works can be best described by citing the following classic books that he wrote on his various research projects:

-- ``Adventures in Theoretical Physics: Selected Papers with Commentaries '' (World Scientific Publishing, January, 2006)
-- ``Quantum Theory as an Emergent Phenomenon'' (Cambridge University Press, 2004).
-- ``Quaternionic Quantum Mechanics and Quantum Fields'' (Oxford University Press, 1995).

During his long career, he held many important positions. He was Divisional Associate Editor for Particles and Fields of Physical Review Letters and also the Chairman of the Division of Particles and Fields of American Physical Society. He was a member of the Editorial Board of Physical Review D and Journal of Mathematical Physics. He is a member of the 'National Academy of Sciences' and Fellow of 'American Physical Society', 'American Academy of Arts and Sciences' and 'American Association for the Advancement of Science'.

Prof. Adler received J.J. Sakurai Prize from American Physical Society in 1988. In 1998 he was awarded the Dirac Medal of the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.

We thought it would be great to hear from Prof. Adler his choice of 5 most important breakthroughs that the Quantum Theory needs.
- 2Physics.com Team]

1. To understand why there are three families of quarks and leptons.

2. To understand the hierarchy problem - why the electroweak scale is so much smaller than the Planck scale.

3. To understand why the cosmological constant is so small.

4. To understand how to get a satisfactory quantum theory of measurement.

5. To reconcile relativistic quantum theory with general relativity.

High Energy Physics: 5 Needed Breakthroughs -- Barry Barish

[Our today's guest in the ongoing feature '5 Breakthroughs' is Prof. Barry Barish (photo courtesy: Caltech).

Barry Barish is a Linde Professor of Physics, Emeritus at the California Institute of Technology, where he taught and conducted research since 1963. He is also the Director of the Global Design Effort for the International Linear Collider.

One of Prof. Barish's noteworthy experiments was at Fermilab using high energy neutrinos to reveal the quark substructure of the nucleon. These experiments were among the first to observe the weak neutral current, a linchpin in the Eletro-Weak unification theory of Glasgow, Salam and Weinberg.

In 1980s Prof. Barish led an international effort to build a sophisticated underground detector (MACRO) in Italy to search for magnetic monopole and solve other related problems in the emerging field of particle astrophysics. The experiment provided the best limits for the Grand Unified magnetic monopoles and some of the key evidences that neutrinos have mass.

In 1994, Prof. Barish became Principal Investigator of the joint Caltech-MIT LIGO project for the detection of gravitational waves and later became Director of the Laboratory from 1997 to 2005.

In 2002 he was nominated to the National Science Board that helps oversee the National Science Foundation (NSF) and advises the President and Congress on policy issues related to science, engineering and education. In 2002 he received the Klopsteg award of the American Association of Physics Teachers (AAPT) and was elected to the National Academy of Sciences. In 2003, he served as a member of the special panel for NASA that considered the future of the Hubble Space Telescope and the transition to the James Webb Space Telescope. Prof. Barish also served as co-chair of the subpanel of the High Energy Physics Advisory Panel (HEPAP) that developed the long-range plan for high energy physics in USA.

Here is Prof. Barish's list of 5 breakthroughs that he would like to see in high energy physics.
-- 2Physics.com Team]

"5 most important breakthroughs that are needed for particle physics:

1) Understanding what is the dark energy in the universe? (We don't even have a good idea here)

2) What is the dark matter? (This is the other big unknown, but at least we have some handles. We know it is non-baryonic and evidence points to either supersymmetric particles, or maybe axions. Perhaps it is neither)

3) What causes mass? (We have a very successful theory of particle physics, but the particles are massless. We need to understand the source of mass. The leading idea is that it is the Higgs mechanism, and we need to see if there is a Higgs particle or variant to make the next step. The Large Hadron Collider at CERN should answer this question)

4) Is the neutrino its own antiparticle? (This is a puzzle going back to Fermi and perhaps the next generation of experiments will resolve it by looking for neutrino-less double beta decay)

5) Is there ultimate unification of the forces of nature? (This is a long term intriguing simplification on our understanding of particles and fields, but present data does not support it. However, if there is a new symmetry in nature (supersymmetry) it could bring this unification.

These are all questions and there is hope we will have much better understanding within a decade or two."

"Existence of Axion" -- R.N. Mohapatra

Rabindra N. Mohapatra (photo courtsey: U. of Maryland)

[This is an invited article. In a recent publication in Physical Review Letters, R.N. Mohapatra (U. of Maryland) and Salah Nasri (U. of Florida) have put forward a theory that can reconcile conflicting results from two experiments that tried to test the existence of "axion" -- an ultralight particle that could make up dark matter. We thank Prof. Mohapatra for contributing this article on our request. -- 2Physics.com Team]

Axions were proposed by Roberto Peccei and Helen Quinn as a way to solve one of the fundamental mysteries of nuclear forces i.e. an inordinately large amount of CP violation in the otherwise successful theory of these forces, Quantum Chromodynamics (QCD) proposed by D. Gross, F. Wilczek and H. D. Politzer. Since their debut into the world of theoretical physics, axions have also been found useful in another context: being ultralight particles (believed to be a billion times or more lighter than the electron) they are capable of populating the Universe so abundantly that they could be candidates for the dark matter of the Universe and thereby resolve another fundamental mystery of cosmology.

Salah Nasri (photo courtsey: U. of Florida)

Because of these twin attributes (solving the problem of QCD and being a candidate for dark matter), considerable amount of research is being devoted to establishing the existence of axions. One of their key properties is that they couple to two photons (one being the magnetic and the other the electric component of light). Therefore interaction of laser beams with strong magnetic fields is considered to be an efficient way to search for them[1].

Two recent attempts that use this technique to search for axions are the CERN CAST (CERN Axion Solar Telescope) experiment[2] and PVLAS experiment at INFN-LNL[3]. The CAST experiment searched for axions produced by light-by-light collision at the center of the Sun and gave a negative result setting strong limits on the axion-photon coupling and its mass. The PVLAS experiment on the other hand looked for axions produced by laser-magnetic field interaction in the laboratory and seems to have a positive evidence for an axion like particle. Their observations can be understood only if the axion-photon coupling are considerably larger than the upper limits set by the CAST result. This has posed a major challenge for theory and in the very least implies that the axion solution to the problems of QCD may be much more complex than previously envisioned or the PVLAS experiment could be the result of completely new kind of phenomenon, not related to the axion.

In a recent Phys. Rev. Lett. Paper [4], we have proposed a new way to reconcile the CAST and the PVLAS results. We use the axion possibility in our approach except the theory has several new features compared to the conventional axion models. We use the phenomenon of phase transition so well known in the study of condensed matter physics (e.g. loss of magnetism of ferromagnets at high temperature). Our basic observation is that the axion photon coupling is not a primordial coupling but is induced by the formation of a vacuum condensate. Therefore the strength of the coupling depends on the environment temperature.

Note that the solar axions are produced at a very high temperature of about 10 million degrees in the core of the Sun whereas the PVLAS axions are produced at room temperature. Therefore if the vacuum condensate responsible for axion-photon coupling undergoes phase transition to zero value in the solar core due to its high temperature, there would be no axion production in the solar core explaining the CAST result. On the other hand, the PVLAS experiment is taking place at the room temperature and therefore the vacuum condensate has nonzero value and the axion-photon coupling is present giving rise to the PVLAS signal for the axion.

This idea is consistent with all known experimental observations in particle physics and astrophysics. We predict that the axion must be accompanied by a twin particle with mass about 100 times that of the electron which undergoes the condensation and is responsible for our effect. It can be produced in the decay of heavy quark bound states, which can provide a way to test our model.

[1] P.Sikivie, Phys. Rev. Lett. 51, 1415 (1983)
[2] S.Andriamonje [CAST Collaboration], arXiv:hep-ex/0702006.
[3] E.Zavattini et al. [PVLAS Collaboration], Nucl. Phys. Proc. Suppl. 164, 264 (2007).
[4] R. N. Mohapatra and S. Nasri, "Reconciling the CAST and PVLAS Results", Phys. Rev. Letters 98, 050402 (2007) Link to Abstract

Large Hadron Collider Data

The LHC is being installed in a tunnel 27 km in circumference, buried 50-175 m below ground. It's located between the Jura mountain range in France and Lake Geneva in Switzerland (photo courtsey CERN)

The Large Hadron Collider (LHC) is the largest scientific instrument of the world. This latest and very powerful particle accelerator is currently being built by CERN, Geneva and is due to switch on in 2007. The physicists and engineers associated with LHC form the largest ever international collaboration in the history of science.

LHC, in its pursuit of deeper understanding of subatomic matter, will ultimately collide beams of protons at an energy of 14 TeV with accelerated beams of lead nuclei, smashing them together with a collision energy of 1150 TeV. For your comparison, 1 TeV (= 10¹²eV) is a unit of energy equivalent to about the energy of motion of a flying mosquito. So, the numbers above may not look very 'high' to you, unless we say that the LHC accelerator will squeeze that much energy into a space about a million million times smaller than a mosquito. That's what makes such particle accelerators so special.

The aim of LHC would be to push our understanding of the fundamental structure of the universe. The results from the LHC might shed light on the existence of dark energy or dark matter and extra dimensions (beyond 3 spatial dimensions and 'time' that Einstein taught us to include), Higgs bosons and other elementary particles predicted by Supersymmetry theory.

The two largest physics collaborations at the LHC, CMS (Compact Muon Solenoid) and ATLAS (A Toroidal LHC ApparatuS), each encompass more than 2,000 physicists and engineers from 170 universities and laboratories. In order to fully exploit the potential for scientific discoveries, the many Petabytes (=10¹² bytes) of data produced by the experiments will be processed, distributed, and analyzed using a global data Grid. The key to discovery is the analysis phase, where individual physicists and small groups repeatedly access, and sometimes extract and transport, Terabyte-scale data samples on demand, in order to optimally select the rare "signals" of new physics from potentially overwhelming "backgrounds" from already-understood particle interactions. This data will amount to many tens of Petabytes in the early years of LHC operation, rising to the Exabyte (=10¹⁸ bytes) range within the coming decade.

In last one year the international team of LHC has achieved some major milestones and set some records in the process of acquiring, storing and transfering such data to research laboratories situated throughout the world. Even before switching on the accelerator and starting physics experiments, the team has already contributed some major breakthroughs in the world of technology.

After all, not very long ago, CERN had given birth to the World Wide Web!

If you are a 'data geek' and get excited by handling, storing and transfering data, you may look at the following postings from our sister website 2Technology:
New Record for Network Data Transfer (Dec 14, 2006)
LHC's New Milestone (Mar 4, 2006)
Fast Network Record (Dec 9, 2005)

B_s meson: Matter to/from Antimatter 3 million times a second

Christoph Paus of MIT announcing the discovery at Fermilab (photo courtsey: Fermilab)

After 2 decades of painstaking research with monumentally precise technology, scientists of the CDF collaboration at the Department of Energy's Fermi National Accelerator Laboratory announced today that they have met the exacting standard to claim discovery of astonishingly rapid transitions of the B_s meson between matter and antimatter 3 trillion times a second.

Immediately after the Big Bang some 13 billion years ago equal amounts of matter and antimatter formed. Much of it quickly acted to annihilate the other, but for little-understood reasons a bit more matter than antimatter survived, providing the universe with the planets, stars and galaxies visible today. Particles that bridge the two worlds, such as the B_s (pronounced B-sub-s) meson, normally don't exist on their own but can be created in the great collisions generated by particle accelerators, which attempt to duplicate conditions close to the Big Bang. Studying the particles helps scientists understand the evolution of the universe.

The B_s meson consists of the heavy bottom quark bound by the strong nuclear interaction to a strange antiquark. The incredibly rapid commuting rate of the B_s meson particle had been predicted by the Standard Model, the successful but still incomplete theory aimed at explaining how matter and energy interact to form the visible universe. The discovery of this oscillatory behavior is thus another reinforcement of the Standard Model's durability.

Many different theoretical models of how the universe works at a fundamental level will now be confronted with the CDF discovery. The currently popular models of supersymmetry, for example, predict a much higher transition frequency than that observed by CDF, and those models will need to be reconsidered.

It must be recalled that scientists at Fermilab also discovered two of the most fundamental particles, the bottom quark in 1977 and in 1995 the top quark, one of the constituent particles of protons, which form the nuclei of atoms.

The results have been submitted in a paper to Physical Review Letters.

Searching CPT Violation

At a fundamental level the nature is ruled by a law of symmetry called the CPT invariance. C stands for charge, P for parity and T for time. So, if we start with a collection of interacting elementary particles and create a mirror-image version (Parity reversal), change the signs on all electrical charges (C) of those particles, and let time run backward, the interactions among the particles would still remain identical to what it was before this CPT transformation.

Since CPT involves space and time operations, any evidence of violation of CPT invariance would mean disruption of he spacetime symmetries embodied in relativity theory and would have far-fetching effect on basic Physics and cosmology. In effect, it would mean that space is not 'isotropic' or that not all directions in space are equivalent. There would be one special direction in space, and the propagation of electromagnetic radiation would be different in different directions depending on its orientation relative to this special direction.


Photo credit: NASA/WMAP Science Team.
WMAP has produced a detailed picture of the infant universe. Colors indicate "warmer" (red) and "cooler" (blue) spots. The white bars show the "polarization" direction of the oldest light.



To look for this effect, scientists at the National Astronomical Observatories in Beijing carefully studied recent measurements of the cosmic microwave background radiation, the remnant of the energy that originated from the big bang and now surrounds the space around us in all directions at approximately 2.9 degree Kelvin. They used data from the satellite-borne Wilkinson Microwave Anisotropy Probe (WMAP) and the BOOMERANG instrument, flown by balloon over Antarctica. These data sets include detailed measurements across the sky of the direction of the electric field, or polarization, of the Cosmic Microwave Background. If CPT symmetry is violated, then all polarizations will rotate with respect to the special space direction as the radiation travels through the universe. In that case the distribution of polarization of all spatial points would not be just random but there would be a specific type of correlation between two points influenced by the existence of such a special direction.

The Chinese team has found signs of this correlation in their analysis, but statistically speaking, it is not yet significant enough and could have arisen from random chance. More detailed investigation would be needed but it's certainly a good brave step in the direction of that more detailed exploration.

Here is the paper: "Searching for CPT Violation With Cosmic Microwave Background Data From WMAP and BOOMERANG", B. Feng, M. Li, J. Q. Xia, X. Chen, and X. Zhang, Phys. Rev. Lett. 96, 221302 (issue of 9 June 2006)

Further Study:
WMAP's introductory page on Cosmic Microwave background
Wikipedia page on Cosmic Microwave Background

Ray Davis (1914-2006)

photo courtsey: Brookhaven National Laboratory, Long Island

Ray Davis, the physics Nobel laureate of 2002, passed away on Wednesday due to complications from Alzheimer's disease at his home in New York. He was 91.

Raymond Davis Jr. was born on Oct. 14, 1914 in Washington, D.C. He received bachelor's and master's degrees in chemistry from the University of Maryland and a doctorate in physical chemistry from Yale University in 1942. Davis spent most of his career (since 1948) at the Brookhaven National Laboratory on Long Island and was a pioneer of neutrino astrophysics.

Neutrinos are small particles that travel at nearly the speed of light, have little or no mass and no charge and interact only extremely rarely with other matter. Neutrinos took centerstage in astrophysics in 1920s. The first hints that the sun was nuclear-powered appeared at that time when experiments showed that a helium atom, which contains two protons and two neutrons, has less mass than four hydrogen atoms -- essentially four protons.

British astrophysicists concluded that the fusion of four hydrogen atoms into a helium atom in the interior of the sun could release substantial amounts of energy, plus two neutrinos. Researchers calculated that only one in trillion solar neutrinos that reached Earth would strike an atomic nucleus, the rest simply passing through unnoticed.

At that time many researchers believed that detection of neutrinos which hardly ever interacts with matter would be impossible. Davis was virtually the only one who thought otherwise. In an audacious experiment, Davis set out to detect these theoretically predicted solar neutrinos. He filled a giant tank with 600,000 litres of "cleaning fluid" (chemists usually call them perchloroethylene) -- 2,300 feet underground in the Barberton Limestone Mine in Ohio in 1961. His team was looking for the occurence of very rare events when a solar neutrino would interact with a chlorine atom to produce radioactive argon. But when he added these signals up, the team found that the Sun was producing only about a third of the neutrinos it should have been based on the best solar models available.

The main problems were coming from cosmic rays and other sources of radiation which were leaking through even the depth of 2300 feet and was causing error in his estimate.

In his second attempt in late 60s Davis installed a 100,000-gallon tank of perchloroethylene 4,850 feet below the ground in the Homestake Gold Mine in Lead, S.D. This time his team synthesized 100 atoms of radioactive argon, added them to the perchloroethylene, then successfully re-extracted them. After much tedious refinements in their observational techniques the detector began observing neutrinos. Over the 30 years of experimentation, about 2,000 neutrino events were observed, demonstrating conclusively the occurrence of nuclear fusion in the sun.

The story didn't end there. In fact a new story began. The number of neutrinos detected by Davis group was only about 1/3rd of the total expected by scientists. This is what came to be known as the "solar neutrino problem." The theoretical models predicting the numbers were developed principally by the late John Bahcall of the Institute for Advanced Study in Princeton, who died in August last year. During those decades strong suspicions were raised at Davis' experiment by several scientists that it was at fault.

Ultimately, other researchers concluded that both Davis and Bahcall were right: the neutrinos produced by the Sun, which are all "electron-type" neutrinos, were oscillating into muon- and tau-like neutrinos on their journey to Earth. These could not interact with chlorine. Those two other types of neutrinos ultimately were observed, but no one would have looked for them had Davis not went forward (despite criticism and scoffing of other researchers who doubted his experiments), fighted with all kinds of challenges offered by the nature and conclusively demonstrated that neutrinos could be detected in the first place.

From time to time in order to advance science to a new level and to open new doors of the universe, we need true leaders who can come forward and accept the challenge and fight against all kinds of adversities offered by nature or man-kind and finally establish the truth and expand the horizon. Raymond Davis Jr was one such leader and he'll be remembered as the physicist who could solve the mystery of the sun.

Proton-Electron Mass Ratio

Spectra of Hydrogen and Mercury

New measurements of starlights suggest that the ratio of the proton's mass to the electron's mass has increased by 0.002% over 12 billion years. The spectra of hydrogen gas as recorded in lab is compared with spectra of light coming from hydrogen clouds billions of light years away when the universe was in its youth.

Molecular hydrogen absorbs light of specific wavelengths, and the resulting spectrum of "absorption lines" uniquely identifies Hydrogen atom by the 'bar' code made up of such lines. The positions of the lines depend on the ratio of the mass of the proton to the mass of the electron. Of course, one needs to carefully take into account the effect of the expansion of the universe which shifts these lines from higher (ultraviolet) to lower (visible) frequency.

The researchers have reported in Physical Review Letters this week that the mass-ratio of proton and electron (the ratio is about 1836 and is denoted by the letter mu) has increased by about 20 parts per million over the past 12 billion years. The proton-to-electron mass ratio figures in setting the scale of the strong nuclear force.

More studies of spectra of Hydrogen gas from distant galaxies are needed to confirm whether the mass ratio has indeed changed.

Here is the link to the abstract of the paper in Physical Review Letters.

Neutrino Oscillation

Photo Courtsey: Fermilab

An international collaboration of scientists at the Department of Energy's Fermi National Accelerator Laboratory have observed the disappearance of muon neutrinos traveling from the lab's site in Illinois to a particle detector in Minnesota. The observation is consistent with an effect known as neutrino oscillation, in which neutrinos change from one kind to another.

Neutrinos are ghost-like particles and rarely interact with matter. In this experiment, they travelled 450 miles straight through the earth from Fermilab to Soudan. They needed no tunnel because they do not interact with matter. The Main Injector Neutrino Oscillation Search (MINOS) experiment studies the neutrino beam using two detectors. The MINOS near detector, located at Fermilab, records the composition of the neutrino beam as it leaves the Fermilab site. The MINOS far detector, located in Minnesota, half a mile underground, again analyzes the neutrino beam. This allows scientists to directly study the oscillation of neutrinos among its 3 types: muon neutrinos, electron neutrinos or tau neutrinos under laboratory conditions.

The abundance of neutrinos in the universe, produced by stars and nuclear processes, may explain how galaxies formed and why antimatter has disappeared. Ultimately, these elusive particles may explain the origin of the neutrons, protons and electrons that make up all the matter in the world around us. The MINOS experiment revealed a value of delta m^2 = 0.0031 eV^2, a quantity that plays a crucial role in neutrino oscillations and hence the role of neutrinos in the evolution of the universe. An accurate measurement of this quantity is essential for understanding quantitatively how neutrinos behave and determine the fate of the universe in certain ways.

The MINOS experiment includes about 150 scientists, engineers, technical specialists, and students from 32 institutions in six countries, including Brazil, France, Greece, Russia, the United Kingdom, and the United States.

Further study:
Discovery of Neutrino Mass and Oscillation
The Neutrino Oscillation Industry

Photon-Photon Scattering

Vacuum is 'a space absolutely devoid of matter'. But according to Quantum ElectroDynamics (QED), particles can still be created in this emptiness of vacuum through light-light interactions. This property follows directly from the quantum nature of the sub-atomic world, to be specific, from the Heisenberg Uncertainty Principle which states that the uncertainty in the position of a particle and the uncertainty of the momentum of a particle are related. A consequence of this principle is that even though there is nothing in the vacuum (no matter or radiation at all), there is still an uncertainty in the amount of energy which can be contained in the vacuum. On average, the energy is constant, however, there is always a slight uncertainty in the energy, which may allow a nonzero energy to exist for short intervals of time. Because of the equivalence between matter and energy, these small energy fluctuations can produce matter (particles) which exists for a short time and then disappears.

In a paper entitled "Using High-Power Lasers for Detection of Elastic Photon-Photon Scattering" published in March 3 issue of Physical Review Letters (Vol.96), Physicists from Umeå University, in Umeå, Sweden, and the Rutherford Appleton Lab, England, propose an experiment to explore the vacuum by aiming three powerful laser streams at each other in 3-dimensional space of the Laboratory (This is important because such proposals mooted earlier had the beams all in a single plane). These three beams will merge to produce a fourth stream with a wavelength shorter than any of the input beams.

The actual experiment is planned to be carried out over the next year at the Rutherford Appleton Lab near Didcot, England. By carefully polarizing the incoming light beams, the number of photons in the output beam can be controlled. This would be an important tool for investigating the parameter space of such a complex experiment, thus providing valuable information about the interactions that took place in the vacuum.

Besides providing good insight into QED itself, this experiment would also be used for testing theories that propose the existence of minor departures from Lorentz invariance which is an important proposition in special relativity that there is no preferred frame of reference. Light-light interactions may also be used to explore various hypotheses related to dark energy that is a hot topic of cosmology nowadays and may provide some clue about the rate and nature of the expansion of the universe.

Owen Chamberlain (1920-2006)

Owen Chamberlain, 1950s (photo courtesy: Lawrence Berkeley National Laboratory)

Nobel Laureate Physicist Owen Chamberlain died yesterday at the age of 85 in his Berkeley home. Owen was a Professor Emeritus of physics at University of California, Berkeley. Chamberlain died quietly in bed from complications of Parkinson's disease, which had plagued him for many years.

He and fellow UC Berkeley physicist Emilio Segrè, both researchers at the former Radiation Laboratory that is now Lawrence Berkeley National Laboratory won the Nobel Prize in Physics in 1959 for their discovery of the antiproton, the antimatter equivalent and negatively-charged mirror image of the proton. This previously postulated subatomic particle was the second antiparticle to be discovered and led directly to the discovery of many additional antiparticles.

Chamberlain worked on the U.S. atom bomb project from 1942 to 1946. He was present at the first atomic bomb test at Alamogordo, New Mexico, in 1945, losing a $5 bet that it would not explode.

Later, while completing his Ph.D. at the University of Chicago, he worked at Argonne National Laboratory, in Illinois. In 1948 he joined the faculty of the University of California at Berkeley, where he became a full professor in 1958. There he conducted research on alpha particle decay, neutron diffraction in liquids, and high-energy nuclear particle reactions.

His proton- and neutron-scattering experiments were conducted with the 184-inch cyclotron at the Radiation Laboratory on the hill above the campus, while his and Segrè's experiments with the antiproton were conducted with the UC Berkeley Bevatron, at the time the largest "atom smasher" in the world. Using it, Chamberlain achieved the first triple-scattering experiment with polarized protons. He and Segrè used the bevatron to produce antiprotons in 1955.

Although he retired in 1989, Chamberlain continued to attend weekly departmental colloquia at Berkeley, including one just last week.

One Decade of Top Quark

A decade ago in this week, experimental physicists representing seventy-four institutions in Brazil, Canada, Colombia, France, India, Italy, Japan, Korea, Mexico, Russia, Taiwan, and the United States announced the discovery at Fermilab of the top quark, a fundamental building block of matter and the universe.

The name "quark" was taken by Murray Gell-Mann from the book "Finnegan's Wake" by James Joyce. The line "Three quarks for Muster Mark..." appears in the fanciful book. Gell-Mann received the 1969 Nobel Prize for his work in classifying elementary particles. There are 6 different kinds of quark: Up, Down, Charm, Strange, Top and Bottom. Being in a confined state, they act as constituents of fundamental particles like Proton and Neutron but not, for instance, electron. The confinement of quarks implies that we cannot isolate them to measure their masses in a direct way. The masses and their existence must be implied indirectly from scattering experiments. To know more about quarks at your own pace, visit
these pages of hyperphysics.

Fermilab will celebrate 10 years of discovery of Top quark and the new possibilities it opened for science in a half-day symposium entitled "Top Turns Ten" on Friday afternoon, October 21, at Fermilab. The agenda is here.