COSMO-2000

The following sections are included:

• Committees

• Preface

• CONTENTS

Cold Dark Matter (CDM) has become the standard modern theory of cosmological structure formation. But despite its many successes, there has been concern about CDM on small scales since the 1994 papers by Flores and Primack and by Moore pointing out the contradiction between the linearly rising rotation curves observed in dwarf galaxies and the 1/r density cusps at the centers of simulated CDM halos. Other CDM issues include the very large number of small satellite halos in simulations, far more than the number of small galaxies observed locally, and possible disagreements between predicted and observed power spectra. The latest data have lessened, although not resolved, many of these concerns. Meanwhile, the main alternatives to CDM that have been considered to solve these problems, self-interacting dark matter (SIDM) and warm dark matter (WDM), have been found to have serious drawbacks.

In this review, the status of measurements of the matter density (Ω_m), the vacuum energy density or cosmological constant (Ω_Λ), the Hubble constant (H₀), and ages of the oldest measured objects (t₀) are summarized. Many recent, independent dynamical measurements are yielding a low value for the matter density (Ω_m ~ 0.3). New evidence from type Ia supernovae suggests that Ω_Λ may be ~0.7. Many recent Hubble constant measurements appear to be converging in the range of 65-75 km/sec/Mpc. Eliminating systematic errors lies at the heart of accurate measurements for all of these parameters.

We first establish the sensitivity range of current experiments of direct search for WIMPs, once the uncertainties in the relevant astrophysical quantities are taken into account. We then analyse the discovery capabilities of these experiments, when their results are analyzed in terms of relic neutralinos. We performe our analysis employing various supersymmetric schemes, and point out the main particle physics uncertainties which have to be taken into account for a correct comparison of theory with experimental data. We evaluate the local and the cosmological densities of the relevant neutralinos and prove that a part of the susy configurations probed by current WIMP experiments entail relic neutralinos of cosmological interest. However, no a priori cosmological constraint is imposed on the analysed supersymmetric configurations.

We consider the neutralino proton cross section for detection of Milky Way dark matter for a number of supergravity models with gauge unification at the GUT scale: models with universal soft breaking (mSUGRA), models with nonuniversal soft breaking, and string inspired D-brane models. The parameter space examined includes m_1/2 <1 TeV and tan β < 50, and the recent Higgs bound of m_h >114 GeV is imposed. (For grand unified models, this bound is to be imposed for all tan β.) All coannihilation effects are included as well as the recent NLO corrections to b → sγ for large tan β, and coannihilation effects are shown to be sensitive to A₀ for large tan β. In all models, current detectors are sampling parts of the paramater space i. e. tan β ≳ 25 for mSUGRA, tan β ≳ 7 for nonuniversal models, and tan β ≳ 20 for D-brane models. Future detectors should be able to cover almost the full parameter space for µ > 0. For µ < 0, cancellations can occur for m_1/2 ≳ 450 GeV, allowing the cross sections to become ≲ 10^-10 pb for limited ranges of tan β. (The positions of these cancellations are seen to be sensitive to the value of σ _πN.) In this case, the gluino and squarks lie above 1 TeV, but still should be accessible to the LHC if m_1/2 < 1 TeV.

Suppose the lightest superpartner (LSP) is observed at colliders, and WIMPs are detected in explicit experiments. We point out that one cannot immediately conclude that cold dark matter (CDM) of the universe has been observed, and we determine what measurements are necessary before such a conclusion is meaningful. We discuss the analogous situation for neutrinos and axions. In both cases there may be no way to determine the actual relic density. It is important to examine this issue for any CDM candidates.

Supersymmetric extensions of the Standard Model which incorporate the axion solution to the strong CP problem necessarily contain also the axino, the fermionic partner of the axion. In contrast to the neutralino and the gravitino, the axino mass is generically not of the order of the supersymmetry breaking scale and can be much smaller. The axino is therefore an intriguing candidate for a stable superpartner. It has been recently shown that axinos are a natural candidate for cold dark matter in the Universe when they are generated non-thermally through out-of-equilibrium neutralino decays. Here, we extend the study of non-thermal production and include a competing thermal production mechanism through scatterings and decays of particles in the plasma. We identify axino masses in the range of tens of MeV to several GeV (depending on a scenario) as corresponding to cold axino relics if the reheating temperature T_R is less than about 5 × 10⁴ GeV. At higher T_R and lower mass, axinos could constitute warm dark matter. In the scenario with axinos as relics the gravitino problem finds a natural solution. The lightest superpartner of the Standard Model spectrum will remain stable in high-energy detectors but may be either neutral or charged. The usual constraint Ω_χh² ≲ 1 on the relic abundance of the lightest neutralino becomes void.

The DAMA experiment is located at the Gran Sasso National Laboratories of the I.N.F.N. and is searching for particle Dark Matter by using various scintillators as target-detector systems. In particular, the results obtained by analysing in terms of WIMP annual modulation signature the data collected with the highly radiopure ≃ 100 kg NaI(Tl) set-up during four annual cycles (total statistics of 57986 kg · day) are here reviewed.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross-section that exclude unexplored parameter space above 10 GeV c^-2 WIMP mass and, at > 75% CL, the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment. The move to a deep site in 2001 should improve the experiment's sensitivity by ~ 100X.

The large N approximation should hold in cosmology even at the origin of the universe. I use ADS–CFT to calculate the effective action and obtain a cosmological model in which inflation is driven by the trace anomaly. Despite having ghosts, this model can agree with observations.

Present data require a spectral index n ≳ 0.95 at something like 1-σ level. If this lower bound survives it will constrain 'new' and 'modular' inflation models, while raising it to 1.00 would rule out all of these models plus many others.

We propose a chaotic inflation model in supergravity. In the model the Kähler potential has a Nambu-Goldstone-like shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. We show that the chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. As an alternative scenario, we also propose new inflation with a chaotic initial condition. In this scenario, chaotic inflation first takes place around the Planck scale, which solves the longevity problem, and also gives an adequate initial condition for new inflation. Then, new inflation lasts long to generate primordial fluctuations for the large scale structure, which generally has a tilted spectrum with the spectral index n_s < 1.

I discuss anthropic selection and related topics.

Recent atmospheric and solar neutrino experiments suggest that neutrinos have small but nonzero masses. They further suggest that mass eigenvalues have certain degree of hierarchical structures, and also some mixing angles are near-maximal while the others are small. We first survey possible explanations for the smallness of neutrino masses. We then discuss some models in which the hierarchical pattern of neutrino masses and mixing angles arises as a consequence of U(1) flavor symmetries which would explain also the hierarchical quark and charged lepton masses.

Compelling evidence for neutrino oscillation was obtained from the Super-Kamiokande's observation of atmospheric neutrinos with Δm² ~ 10^-3 eV². There are two other indications of neutrino oscillation with different Δm² from solar neutrino observations and the LSND experiment. On the other hand, an important bound was obtained by the CHOOZ reactor neutrino oscillation experiment. The results from these experiments as well as some other neutrino oscillation experiments are reviewed. Particular emphasis is placed on the recent results from Super-Kamiokande, which were updated in June, 2000. In addition, the status of the K2K experiment and the prospects of forthcoming neutrino oscillation experiments are reviewed.

PAMELA is a satellite-borne experiment whose main physics goals are the search for cosmic antimatter of primary origin and the measurement of the spectrum of cosmic ray particles and antiparticles in the energy range from ~50 Mev to 200 GeV and beyond.

Additional objectives are the continuous monitoring of the cosmic ray solar modulation, the study of the solar flares and the stationary perturbed fluxes in the Earth magnetosphere.

The PAMELA apparatus will fly in a low polar sun-synchronous orbit for at least three years. It consists of a magnetic spectrometer with a particle identification system.

The scientific objectives, the mission profile and a general description of the instrument are presented.

The fundamental problem of how tunneling in thermal medium is completed is addressed, and a new time scale of order 1/friction for its termination, which is usually much shorter than the Hubble time, is pointed out. Enhanced non-linear resonance is responsible for this short time scale. This phenomenon occurs when the semiclassical periodic motion in a metastable potential well resonates with one of the environment harmonic oscillators coupled to its motion.

Although the cosmological constant has primarily cosmological consequences, its smallness poses one of the basic problems in particle physics. Various attempts have been made to explain this mystery, but no satisfactory solution has been found yet. The appearance of extra dimensions in the framework of brane world systems seems to provide some new ideas to address this problem form a different point of view. We shall discuss some of these new approaches and see whether or not they lead to an improvement of the situation. We shall conclude that we are still far from a solution of the problem.

I give a brief informal introduction to the idea and tests of large extra dimensions, focusing on the case in which the space-time manifold has a direct product structure. I then describe some attractive implementations in which the internal space comprises a compact hyperbolic manifold. This construction yields an exponential hierarchy between the usual Planck scale and the true fundamental scale of physics by tuning only coefficients, since the linear size of the internal space remains small. In addition, this allows an early universe cosmology with normal evolution up to substantial temperatures, and completely evades astrophysical constraints.

Phenomenology of a radion (ɸ) in the Randall-Sundrum scenario is discussed. The radion couples to the trace of energy momentum tensor of the standard model with a strength suppressed only by a new scale (Λ_ɸ) which is an order of the electroweak scale. In particular, the effective coupling of a radion to two gluons is enhanced due to the trace anomaly of QCD. Therefore, its production cross section at hadron colliders could be enhanced, and the dominant decay mode of a relatively light radion is ɸ → gg, unlike the SM Higgs boson case. We also present constraints on the mass m_ɸ and the new scale Λ_ɸ from the Higgs search limit at LEP, perturbative unitarity bound and the stability of the radion/Higgs potential under radiative corrections.

There are many interesting issues in the brane world with a large/warped extra dimension. We focus on the cosmological aspects. We review the cosmological solutions of the brane world and how the conventional four-dimensional cosmology is recovered by including the effect of stabilization. Its implications on the mass hierarchy and the cosmological constant are discussed.

We study precise calculation of neutralino relic density in the minimal supergravity model. We compare the exact formula for the thermal average of the neutralino annihilation cross section times relative velocity with the expansion formula in terms of the temperature, including all the contributions to neutralino annihilation cross section analytically. We confirm that the expansion formula fails badly near s-channel poles. We show that the expansion method causes 5-10 % error even far away from the poles.

Microlensing distant stars by non-compact objects such as neutralino stars is considered. Recently Gurevich and Zybin considered the objects as microlenses. Using the non-singular density distribution we analyse microlensing by non-compact objects. We obtain the analytical solutions of the gravitational lens equation and the analytical expression for the amplification factor of the gravitational lens. We show that using the model of microlensing by non-compact objects it is possible to interpret microlensing event candidates having two typical maximums of light curves which are usually interpreted as binary microlenses.

We report a feasibility study of CsI(Tl) scintillator to use for an experiment of dark matter search. The intrinsic backgrounds from the internal radioisotopes of CsI(Tl) are studied. The photomultiplier tubes matching better for CsI(Tl) has been studied. We also investigated the pulse shape discrimination power of this scintillator using the low energy alpha source. The overall sensitivities expected with this scintillator for future dark matter experiment is estimated.

The grand unification scale M_G ~ 10¹⁶ GeV can generate the inflation scale M_I ~ 10^13-14 GeV for small inflaton coupling. We show that in this case the scale of supersymmetry breaking, M_S ~ 10¹⁰ GeV may dominate the dynamics of the inflationary phase. We study this effect in a hybrid inflation model whose ground state breaks supersymmetry.

The power spectra of the scalar- and tensor-type structures generated in an inflation model based on a massive nonminimally coupled scalar field are derived. The contributions of these structures to the anisotropy of the cosmic microwave background radiation are compared with the four-year COBE DMR data. The constraints on the expansion rate during the inflation period, and the relative amount of the tensor-type contribution to the quadrupole of the CMBR temperature anisotropy are provided.

We analyze the effect of primordial density perturbations on the cosmic QCD phase transition. According to our results hadron bubbles nucleate at the cold perturbations. We call this mechanism inhomogeneous nucleation. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.

This article is written for the proceedings of the international workshop COSMO 2000 (Sept.4 - Sept.8). The talk I gave there and this article are based on the work Phys.Lett.B484:103(2000)¹ with Yasunori Nomura(UC Berkeley) and T. Yanagida(Univ. of Tokyo), and include further discussion on the cosmological coincidence problem.

The early Universe inflation¹¹ is well known as a promising theory to explain the origin of large scale structure of the Universe, that is, an established causal theory for the origin of primordial density fluctuations which may interpret the observed density inhomogeneities and cosmic microwave fluctuations in the very early Universe. This theoretical framework can solve the early universe pressing problems in the standard Hot Big Bang theory¹. In the single field inflation model, we study the possibilitis of parametric amplification of the gravitational perturbation, and we find that there is no additional growth of the super-horizon modes during reheating beyond the usual predictions by giving a general analytic explanation as well as the numerical results for it.

Recently it is claimed that the creation of multiple winding topological defects may play an important role in the scenario of electroweak baryogenesis, topological inflation and primordial black hole formation. The number density of such defects in the early universe is estimated and their cosmological implications will be discussed.

We consider the Q-ball formation, and its implication to cosmology in the context of gauge-mediated SUSY breaking in minimal supersymmetric standard model. In addition to the usual stable Q ball investigated in the literature, we obtain a new type of a stable Q ball. It is so-called gravity-mediation type of Q ball, but also stable against the decay into nucleons, since the energy per unit charge is equal to gravitino mass m_3/2, which can be smaller than nucleon mass in the gauge-mediation mechanism. We consider the cosmological consequences in this new Q-ball scenario, and find that this new type of the Q ball can be considered as the dark matter and the source for the baryon number of the universe simultaneously.

It has recently been suggested that the baryon washout problem of standard electroweak baryogenesis could be avoided if inflation ends at a low enough energy density and a parametric resonance transfers its energy repidly into the standard model fields. We present preliminary results of numerical simulations in a SU(2)×U(l) gauge-Higgs model in which this process was studied.

We present non-perturbative analysis of fermion production during preheating in the presence of multiple scalar fields in an expanding background paying particular attention to the interplay between instant preheating (χ-ψ) and direct fermion preheating (ɸ-ψ). In the broad resonance regime we find that instant fermion production is sensitive to suppression of the long wavelength χ modes during inflation. Further, the standard scenario of resonant fermionic preheating through inflaton decay can be significantly modified by the χ-ψ coupling, and may even lead to a decrease in the number of fermions produced.

The evolutions of linear structures in a spatially homogeneous and isotropic world model are characterized by some conserved quantities. The amplitude of gravitational wave is conserved in the super-horizon scale, the perturbed three-space curvature in the comoving gauge is conserved in the super-sound-horizon scale, and the angular momentum of rotational perturbation is generally conserved.

In this talk, we present the recent progress on the primordial nucleosynthesis due to the photo-dissociation of light elements caused by the decay of a massive particle after the standard big-bang nucleosynthesis epoch. Especially, very recently it was reported by the other group that the non-thermal production of ⁶Li constrains the number density of the parent massive particles most severely. Here we show that the theoretical prediction of ⁶Li abundance is uncertain due to lack of the experimental data of the cross sections, and the observational value has large errors. Therefore we find ³He overproduction due to ⁴He photodissociation still gives the strongest constraint. Then compared to the observational light element abundances, we can constrain the model of the inflation scenario and particle physics.

Leptogenesis with Affleck-Dine mechanism is investigated. We find that an extremely small mass for the neutrino m_ν ≲ 10^-8 eV is required to obtain the desired baryon asymmetry in the present universe. We also propose a model to avoid such an ultralight neutrino, where the mass can be as large as 10^-4 eV.

The observed Helium abundance is in marginal disagreement with the prediction of the standard Big Bang Nucleosynthesis model. We show that non-minimally quintessence model may help to reduce the possible breach between theory and observation.

I briefly review some of recent developments on color superconductivity and discuss the neutrino interaction in color superconductors which might exist in the core of compact stars. Then, I discuss the possible implications of color superconductivity on the cooling of neutron stars.

Using lattice gauge theory simulation, we investigate non-perturbative triviality of QED. Difficult problems with chiral limit is avoided by adding a small Z(2) symmetric four fermi interaction. The added term is irrelevant and its effect should disappear in the continuum limit. Furthermore, this term separates the phase transition associated with monopoles from the phase transition associated with chiral symmetry, which allows us to concentrate on the chiral phase transition. Our result extends perturbative triviality of QED to a non-perturbative regime.

Berezinsky, Hnatyk and Vilenkin showed that superconducting cosmic strings could be central engines for cosmological gamma-ray bursts and for producing the neutrino component of ultra-high energy cosmic rays. A consequence of this mechanism would be that a detectable cusp-triggered gravitational wave burst should be released simultaneously with the γ-ray surge. If contemporary measurements of both γ and ν radiation could be made for any particular source, then the cosmological time-delay between them might be useful for putting unprecedently tight bounds on the neutrino mass spectrum. Such measurements could consistently verify or rule out the model, since strictly correlated behaviour is expected for the duration of the event and for the time variability of the spectra.

From the BPS equations of junctions of domain walls, we consider a stable hexagonal configuration of network of brane-worlds, which are only approximately locally BPS. We propose a model for a mechanism of supersymmetry breaking, where a messenger for the SUSY breaking comes from the neighboring anti-BPS junction world, propagating along the domain walls connection them. We also consider implication to Dark Matter problem. We consider modification of the Newton's force law for brane world consisting of periodic configuration of branes, which supports a massless graviton. It is well separated from the Kaluza-Klein spectrum by a mass gap. As another application of recent development of string theory to Cosmology, we consider the Casimir effect on compact noncommutative space. We suggest a stabilization mechanism for a senario in Kaluza-Klein theory, where some of the extra dimensions are noncommutative.

We show that the Gauss-Bonnet term is the only consistent curvature squared interaction in the Randall-Sundrum model and various static and inflationary solutions can be found. And from metric perturbations around the RS background with a single brane embedded, we also show that for a vanishing Gauss-Bonnet coefficient, the brane bending allows us to reproduce the 4D Einstein gravity at the linearized level.

We provide the exact time-dependent cosmological solutions in the Randall-Sundrum (RS) setup with bulk matter, which may be smoothly connected to the static RS metric. In the static limit of the extra dimension, the solutions are reduced to the standard Friedmann equations. In view of our solutions, we also propose an explanation for how the extra dimension is stabilized in spite of a flat modulus potential at the classical level.

Using the warped extra dimension geometry of the many-brane extension of the Randall-Sundrum solution, we find a natural explanation for the observed quark masses of the three Standard Model (SM) generations. Localizing massless SM matter generations on neighboring 3-branes in an extra dimensional world leads to phenomenologically acceptable effective four dimensional masses arising from the coupling of the fermion field with the background metric. Thus this geometry can simultaneously address the gauge and quark mass hierarchy problems.

We consider Randall-Sundrum(RS) model in generalized gravities and see that the localization of gravity happens in generic situations though its effectiveness depends on the details of the configuration. It is shown that RS picture is robust against quantum gravity corrections (ɸR) as long as the correction is reasonably small. We extend our consideration to the model of scalar coupled gravity (Brans-Dicke theory) which leads us to the specific comparison between RS model and inflation models. The exponential and power law hierarchy in RS model are shown to correspond to the exponential and power law inflation respectively.

We construct dynamically a black p-brane world of an exponentially decaying warped factor in arbitrary but larger than one extra-dimensions. Our fine tuned brane world is identified by the interior of an extremal charged black hole.

We consider a brane world residing in the interior region inside the horizon of extreme black branes. In this picture, the size of the horizon can be interpreted as the compactification size. The large mass hierarchy is simply translated into the large horizon size, which is provided by the magnitude of charges carried by the black branes. Hence, the macroscopic compactification size is a quantity calculable from the microscopic theory which has only one physical scale, and its stabilization is guaranteed from the charge conservation.

The following Sections are included:

• List of Participants

• Program