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