Cosmic Connections - Ft

CONFERENCES Cosmic connections - ft

Two conferences last summer explored the increasing areas of common ground between COSMO-02 views the universe from Chicago

Christian Armendâriz-Picôn and

Géraldine Servant report from the sixth New results from the DASI telescope (left), confirming the standard the conference in the COSMO series. intensity and polarization map (right) shows a 5 degree square portion denote the temperature of the radiation. (DASI.)

Last September, the 265 seats of Chicago's Adler Planetarium, on unprecedented accuracy (by cosmological standards). Moreover, the Lake Michigan shoreline, were filled with participants at the ongoing or planned projects, such as large-scale structure cata COSMO-02 International Workshop on Particle Physics and the Early logues (2dF, SDSS), cosmic microwave background maps (MAP, Universe. The conference was co-organized by the Center for Planck) and supernova surveys (ESSENCE, SNAP) will soon allow Cosmological Physics at the University of Chicago, the Adler further significant reductions in the error bars. These precision mea Planetarium and the Theoretical Astrophysics Group at Fermi surements will help us to refine our understanding of the universe, National Accelerator Laboratory. COSMO conferences provide a and will certainly shed light on what is currently the most challeng forum for particle physicists, cosmologists and astrophysicists to ing puzzle for cosmologists and particle physicists - the nature of discuss new results in the exciting and fast-moving field of particle dark energy. This is currently the dominant energy component of astrophysics and cosmology. One of the new features this year was the universe that causes its expansion to accelerate. the presence of string theorists, showing that the latest cosmologi On the theoretical side, the standard model of cosmology rests on cal observations have attracted the attention of a very large and two pillars: cold dark matter (CDM) and inflation. In a CDM cos diverse physics community. mology, most of the matter of the universe consists of non-baryonic, The conference opened with a talk by Wendy Freedman of non-relativistic and collisionless particles. Numerical simulations Carnegie, who addressed the recent emergence of a "standard show that the gravitational attraction between these particles yields model" in cosmology. From an observational point of view, our uni structures - galaxies, clusters and superclusters - that agree with verse can be described by only a few parameters, such as the the ones observed in the universe, possibly up to certain discrep Hubble "constant" and the contribution of the different constituents ancies at subgalactic scales. The potential problems of the CDM of the universe to the total energy density. As Robert Kirshner of scenario and the properties of some alternative scenarios, such as Harvard, David Weinberg of Ohio and Tim McKay of Michigan self-interacting dark matter or modified Newtonian dynamics, were pointed out, a combination of the results of different cosmological critically discussed by Marc Kamionkowski of Caltech and Arthur observations already allows us to measure those parameters with Kosowsky of Rutgers. At this stage it is still disputed whether the

26 CERN Courier March 2003 CONFERENCES! )m dark matter to strings

physics of elementary particles and the larger-scale studies of astrophysics and cosmology.

Essentially the same mecha nism that explains the origin of primordial density perturba tions - quantum fluctuations of the inflation field - seems to imply that inflation will be eter nal. As discussed by Alan Guth of MIT, who also delivered a widely attended public lecture at the Adler Planetarium, an inflating universe resembles a fractal. In a given inflating region of the universe, inflation has a finite lifetime, but at any given moment of time, there are always patches of the uni verse that continue to inflate. It is unclear whether such a pre Earl Lavon "Von" Freeman - a diction can be experimentally living legend of Chicago jazz tested, but it certainly poses (tenor) saxophone - was the dramatic views on the global about the origin of the CMB, were a major highlight at C0SM0-02. DASI's star at the conference structure of the universe. he CMB sky. The lines show the axis of the polarization, and the colours banquet, where he played with An important confirmation his quartet. that our theoretical under standing about CMB fluctua CDM scenario is free of problems, but as the talk by Andreas tions is on the right track came with the announcement by John Albrecht of Davis suggested, it is fair to say that theorists continue to Carlstrom of Chicago of the first measurement of CMB polarization be in the dark regarding dark energy. by the DASI experiment. According to the standard theory, the tem perature anisotropies we observe in the CMB are due to acoustic Inflation goes on and on oscillations of the primordial baryon-radiation plasma. If this is true, Inflation remains one of the cornerstones of modern cosmology. the light that last scattered at the time of recombination - i.e. the According to the inflationary paradigm, the early universe experi CMB - should be partially polarized. The measurement of such enced a stage of accelerated expansion. As a result of this expan polarization is a success of the standard theory, and represents the sion, inflation produces a homogeneous and flat universe, as first step towards more ambitious measurements of the properties confirmed by cosmic microwave background (CMB) measurements. of the CMB polarization. As Alessandra Buonanno of Paris pointed Inflation also explains the origin of the tiny primordial density fluctu out, the sea of relic gravitational waves that inflation predicts should ations that developed into galaxies and clusters by gravitational insta leave a characteristic imprint on the polarization pattern of the CMB. bility. David Wands of Portsmouth described how inflation relates This imprint could be used to determine the amplitude of gravita these primordial density perturbations to quantum fluctuations of tional waves produced during inflation, which in turn fixes the energy the scalar field that drives inflation. Despite the fact that there is scale at which inflation took place. no theoretically preferred inflationary scenario, most inflationary Because of the high-energy scale at which inflation is expected to models make definite predictions about the properties of these pri take place (around 1015 GeV in the simplest models), the primordial mordial density perturbations. They should be Gaussian, adiabatic perturbations generated during inflation might be our only hope of and nearly scale-invariant. These predictions have been confirmed probing the physics close to the Planck scale. This possibility was in an impressive series of experiments, and as Lloyd Knox of Davis explored in a plenary talk by Nemanja Kaloper of Davis. Although in reported, new CMB missions, such as the MAP and Planck satel some inflationary models, Planck-scale suppressed corrections may lites, will further test, scrutinize and constrain inflationary models. leave an observable imprint in the primordial spectrum, Kaloper >l

CERN Courier March 2003 27 by the LHC with a great degree of complementarity with direct (elastic scattering) and indirect (signals from its cosmic annihilation) neu tralino searches. The status of other supersymmetric dark matter can didates was reviewed (sneutrinos: ruled out; gravitinos: safe) as well as the recently proposed TeV mass Kaluza-Klein dark matter can didate, which will also be probed at the LHC. As for non-accelerator searches of CDM candidates, Maryvonne De Jesus of Lyon reported the results from and prospects for the numerous ongoing and planned direct searches for WIMPs via elastic scattering experiments, while Georg Raffelt of MPI, Munich, described the status of axion searches. Regarding baryogenesis, the theory of electroweak baryogenesis in the Minimal Supersymmetric Standard Model (MSSM), which Participants at the COSMO-02 conference enjoy a break was reviewed by Mariano Quiros as well as Mark Trodden, has excit against a Chicago skyline. ing prospects. The remaining very tiny corner of parameter space for which it works corresponds to a light Higgs and a light stop. argued that generically, such an imprint is expected to be too small Those should be found byTevatron Run II if the MSSM is consistent to be observable in ongoing experiments. Such a conclusion was with electroweak baryogenesis. also the subject of a lively debate in the parallel sessions. Other important activities led by high-energy physicists were emphasized at the conference - in particular, B physics will teach us Neutrinos, neutralinos and WIMPs about the sources of CP violation. Still in the domain of flavours, The major experimental accomplishment in particle physics in experiments with neutrino beams (such as MiniBooNE at FNAL) will recent years has been the evidence for non-vanishing neutrino help us to understand neutrino flavours. And finally, we heard that masses from solar and atmospheric neutrinos. This has provided "electroweak precision measurements are not boring": the mea the first solid hint of physics beyond the Standard Model. While neu surement of the anomalous magnetic moment of the muon at trino oscillation experiments provide information on the neutrino Brookhaven, the electroweak mixing angle by the NuTeV collabora mass squared difference, the absolute scale of neutrino masses is tion, and the bottom quark forward-backward asymmetry at LEP so far unknown. To date, as Alexander Dolgov of INFN Ferrara men look like anomalies in the present global fit to electroweak data,

tioned in his talk, "astronomy opens the best way to measure mv." and could be a sign of new physics. Big Bang nucleosynthesis, large-scale structure and CMB radiation constrain the contribution of massive neutrinos to the total mass Extra dimensions and strings density. A recent limit obtained in the 2 Degree Field (2dF) galaxy The field of extradimensional cosmology was well represented in redshift survey gives an upper bound on the sum of neutrino mass plenary talks by Ruth Gregory of Durham, Lev Kofman of Toronto eigenvalues 2,m,< 1.8 eV. In the near future, the Sloan Digital Sky and Lisa Randall of Harvard. Extradimensional cosmology is very rich, Survey, combined with the CMB data of the MAP satellite, should but it is still in its infancy, and there is much left to explore. The evo

reach a sensitivity of 2mv«0.65 eV. As far as sterile neutrinos are lution of the universe at late times can be described within the con concerned, George Fuller of San Diego devoted an entire plenary text of extradimensional cosmology, or in other words, the presence talk to their effects on the dynamics of the universe and how cos of extra dimensions can be reconciled with constraints from late-time mology can constrain them. cosmology. On the other hand, extradimensional cosmology at early One of the fundamental unsolved questions of astroparticle times is much more difficult to understand. There is no experimental physics is the origin of ultra-high-energy cosmic rays, a topic that was constraint to guide model-builders overwhelmed by an excessive reviewed by Gunter Sigl of Paris. To understand the acceleration and freedom. Kofman reported new ideas on inflation from extra dimen sky distribution of cosmic rays, a better knowledge of the strength sions (for example colliding branes and radion potentials), as well and distribution of cosmic magnetic fields is needed. Sigl stressed as recent work on string signatures on cosmological observations. that ultra-high-energy cosmic rays with energies above 1018eV Regarding attempts by particle theorists to explain dark energy with involve centre of mass energies above 1 TeV, which are beyond the something other than a cosmological constant, Maxim Perelstein of reach of accelerator experiments. They thus provide a low-cost lab Berkeley discussed networks of domain walls - quite generic in oratory to probe potential new physics beyond the electroweak scale. attempts to go beyond the Standard Model of particle physics. The question "How can particle accelerators directly attack major Another proposal to interpret supernovae data, presented by John cosmological issues?" was addressed by Joe Lykken of Fermilab. Terning of Los Alamos, is to introduce photon-axion oscillations in The two main topics about which both theorists and experimentalists an intergalactic magnetic field as a way of rendering supernovae in particle physics have much to say are dark matter and baryogen- dimmer, an explanation that does not need cosmic acceleration esis. If supersymmetry has anything to do with the stabilization of the (but still requires a dark energy component of negative pressure). electroweak scale, the superparticles are expected to be seen at the Joe Polchinski of Santa Barbara addressed the question "Does LHC, and the hypothesis of a neutralino as a dark matter candidate - string theory have vacua like ours, i.e. with (nearly) zero cosmolog also discussed by Leszek Roszkowski of Lancaster - will be covered ical constant, a non supersymmetric spectrum and a stable (or long- by the LHC with a great degree of complementarity with direct (elastic scattering) and indirect (signals from its cosmic annihilation) neu tralino searches. The status of other supersymmetric dark matter can didates was reviewed (sneutrinos: ruled out; gravitinos: safe) as well as the recently proposed TeV mass Kaluza-Klein dark matter can didate, which will also be probed at the LHC. As for non-accelerator searches of CDM candidates, Maryvonne De Jesus of Lyon reported the results from and prospects for the numerous ongoing and planned direct searches for WIMPs via elastic scattering experiments, while Georg Raffelt of MPI, Munich, described the status of axion searches. Regarding baryogenesis, the theory of electroweak baryogenesis in the Minimal Supersymmetric Standard Model (MSSM), which Participants at the COSMO-02 conference enjoy a break was reviewed by Mariano Quiros as well as Mark Trodden, has excit against a Chicago skyline. ing prospects. The remaining very tiny corner of parameter space for which it works corresponds to a light Higgs and a light stop. argued that generically, such an imprint is expected to be too small Those should be found byTevatron Run II if the MSSM is consistent to be observable in ongoing experiments. Such a conclusion was with electroweak baryogenesis. also the subject of a lively debate in the parallel sessions. Other important activities led by high-energy physicists were emphasized at the conference - in particular, B physics will teach us Neutrinos, neutralinos and WIMPs about the sources of CP violation. Still in the domain of flavours, The major experimental accomplishment in particle physics in experiments with neutrino beams (such as MiniBooNE at FNAL) will recent years has been the evidence for non-vanishing neutrino help us to understand neutrino flavours. And finally, we heard that masses from solar and atmospheric neutrinos. This has provided "electroweak precision measurements are not boring": the mea the first solid hint of physics beyond the Standard Model. While neu surement of the anomalous magnetic moment of the muon at trino oscillation experiments provide information on the neutrino Brookhaven, the electroweak mixing angle by the NuTeV collabora mass squared difference, the absolute scale of neutrino masses is tion, and the bottom quark forward-backward asymmetry at LEP so far unknown. To date, as Alexander Dolgov of INFN Ferrara men look like anomalies in the present global fit to electroweak data,

reach a sensitivity of 2mv«0.65 eV. As far as sterile neutrinos are lution of the universe at late times can be described within the con concerned, George Fuller of San Diego devoted an entire plenary text of extradimensional cosmology, or in other words, the presence talk to their effects on the dynamics of the universe and how cos of extra dimensions can be reconciled with constraints from late-time mology can constrain them. cosmology. On the other hand, extradimensional cosmology at early One of the fundamental unsolved questions of astroparticle times is much more difficult to understand. There is no experimental physics is the origin of ultra-high-energy cosmic rays, a topic that was constraint to guide model-builders overwhelmed by an excessive reviewed by Gunter Sigl of Paris. To understand the acceleration and freedom. Kofman reported new ideas on inflation from extra dimen sky distribution of cosmic rays, a better knowledge of the strength sions (for example colliding branes and radion potentials), as well and distribution of cosmic magnetic fields is needed. Sigl stressed as recent work on string signatures on cosmological observations. that ultra-high-energy cosmic rays with energies above 1018eV Regarding attempts by particle theorists to explain dark energy with involve centre of mass energies above 1 TeV, which are beyond the something other than a cosmological constant, Maxim Perelstein of reach of accelerator experiments. They thus provide a low-cost lab Berkeley discussed networks of domain walls - quite generic in oratory to probe potential new physics beyond the electroweak scale. attempts to go beyond the Standard Model of particle physics. The question "How can particle accelerators directly attack major Another proposal to interpret supernovae data, presented by John cosmological issues?" was addressed by Joe Lykken of Fermilab. Terning of Los Alamos, is to introduce photon-axion oscillations in The two main topics about which both theorists and experimentalists an intergalactic magnetic field as a way of rendering supernovae in particle physics have much to say are dark matter and baryogen- dimmer, an explanation that does not need cosmic acceleration esis. If supersymmetry has anything to do with the stabilization of the (but still requires a dark energy component of negative pressure). electroweak scale, the superparticles are expected to be seen at the Joe Polchinski of Santa Barbara addressed the question "Does LHC, and the hypothesis of a neutralino as a dark matter candidate - string theory have vacua like ours, i.e. with (nearly) zero cosmolog also discussed by Leszek Roszkowski of Lancaster - will be covered ical constant, a non supersymmetric spectrum and a stable (or long- lived) vacuum?" To date, there is no positive satisfying answer to ference was envy: "This is a golden age of cosmology: beautiful this question. Polchinski also showed how the simplest string mod observations and the emergence of a standard model." He made uli potentials have difficulty in describing "quintessence". the comparison with the situation he experienced 30 years ago Will string theory lead to a theory of the Big Bang? Nathan Seiberg when the Standard Model of particle physics was emerging. of Princeton explained how string theorists are trying to address the Astrophysical observations represent a testing ground for funda problem of cosmological singularities, and presented the new chal mental physics; experimental cosmology will provide increasingly lenges and recent explorations in the field of time-dependent solu precise tests of the Standard Model and constraints on new physics. tions in string theory. In a very different approach, Willy Fischler of Texas presented a new cosmological model in which the primordial Further reading universe is dominated by a dense gas of black holes. Both plenary (including streaming video) and parallel talks are avail The question of whether string theory will yield the principle that able online at http://pancake.uchicago.edu/~cosmo02/. determines the history of the universe was also raised by David Gross of Santa Barbara, who gave the closing talk of the confer Christian Armendariz-Picon and Géraldine Servant, University ence. Gross confessed that his major feeling at the end of the con- of Chicago. Neutrinos lead beyond the desert The Finnish town of Oulu, on the Gulf of Participants of the Beyond 2002 conference included (first row, Bothnia, almost at the Arctic Circle, left to right, sitting): Rabindra Mohapatra, Dick Arnowitt, provided a pleasant atmosphere for a Masato Morita, Hans V Klapdor-Kleingrothaus (chairman of the meeting), Yuha Peltoniemi (co-chairman); second row, from left, conference on particle physics beyond the sitting: Dimitri Nanopoulos, Dharam Ahluwalia; second row, from left, standing: Raoul Viollier, Irina Krivosheina, Birgitt Standard Model. Brusila (conference secretary), Tom Kuo and Anne Green.

The Beyond the Desert 02 - Accelerator, Non-accelerator and Space talking about string and D-brane physics at low energies, pointed Approaches conference was held on 2-7 June 2002. It was the out that although no-one has ever observed strings or the space of third in the series of "Beyond conferences" that began in 1997 extra dimensions where they live, the "hidden" dimensions of string (CERN Courier November 1997 pl6). Traditionally the scientific pro theory may be much larger than we thought in the past, and may gramme has covered almost all of modern particle physics, and this come within experimental reach in the near future. meeting was no exception, ranging from SUSY and extra dimensions The long-standing and very intriguing problem of dark matter in to dark matter and neutrino mass. the universe, with its connection to new physics and new phenom The conference began with sessions on new theoretical develop ena, was another important topic. Results and perspectives for ments in extending the Standard Model by means of grand unified direct dark matter experiments with scintillators (DAMA and LIBRA) and SUSY theories, followed by new results on the search for and germanium detectors with big target mass (GENIUS and Higgses, SUSY particles, R-parity violation, leptoquarks and excited GENIUS-TF) were presented by Rita Bernabei of Roma and Irina V fermions at the LEP and HERA colliders. The revival of a g-2 signal for Krivosheina of Heidelberg and Nizhnij Novgorod. These are currently the muon deviating from the Standard Model, and its consequences the only two experiments that can in principle use seasonal modu for SUGRA models, were addressed by Pran Nath of Boston who, lation to see (and indeed DAMA has seen) a positive signal from the together with Dick Arnowitt of Texas, first introduced SUGRA interactions of dark matter particles by direct detection. Other 20 years ago. Later, extra dimensions, M-theory and fundamental experiments, for example with sophisticated cryogenic detectors symmetries were also presented. Ignatios Antoniadis of CERN, while exploiting ionization (or scintiIlation)-to-heat discrimination, are t>