D-Term Inflation: The Good, the Bad and the Ugly

An inflationary stage dominated by a D-term avoids the slow-roll problem of inflation in supergravity and can naturally emerge in theories with a non-anomalous or anomalous U(1) gauge symmetry. In this talk different aspects of D-term inflation are discussed.Comment: 6 pages, LaTeX file, uses sprocl.sty. Based on the invited plenary talk given at the COSMO97 Conference, Ambleside, England, September 15-19 1997 and on the talk given at the Phenomenological Aspects of Superstring Theories (PAST97) Conference, ICTP Trieste, Italy, October 2-4 1997. To appear in the Proceeding

Multigraviton Scattering in the Matrix Model

We consider scattering processes in the matrix model with three incoming and three outgoing gravitons. We find a discrepancy between the amplitude calculated from the matrix model and the supergravity prediction. Possible sources for this discrepancy are discussed.Comment: 11 pages, latex, references adde

Electroweak Symmetry Breaking due to Confinement

Within the framework of gauge mediated supersymmetry breaking, we consider an electroweak symmetry breaking pattern in which there is no conventional $\mu$ term. The pattern is made appealing through realizing it as low energy effective description of a supersymmetric Yang-Mills theory which is of confinement. Phenomenological implications are discussed.Comment: 8 pages, revtex, no figure, the discussion on effective superpotential refine

Resonant decay of flat directions

We study preheating, i.e., non-perturbative resonant decay, of flat direction fields, concentrating on MSSM flat directions and the right handed sneutrino. The difference between inflaton preheating and flaton preheating, is that the potential is more constraint in the latter case. The effects of a complex driving field, quartic couplings in the potential, and the presence of a thermal bath are important and cannot be neglected. Preheating of MSSM flat directions is typically delayed due to out-of-phase oscillations of the real and imaginary components and may be preceded by perturbative decay or $Q$-ball formation. Particle production due to the violation of adiabaticity is expected to be inefficient due to back reaction effects. For a small initial sneutrino VEV, $\lesssim m_N/h$ with $m_N$ the mass of the right handed sneutrino and $h$ a yakawa coupling, there are tachyonic instabilities. The $D$-term quartic couplings do not generate an effective mass for the tachyonic modes, making it an efficient decay channel. It is unclear how thermal scattering affects the resonance.Comment: 20 pages, 4 figure

"Nonbaryonic" Dark Matter as Baryonic Color Superconductor

We discuss a novel cold dark matter candidate which is formed from the ordinary quarks during the QCD phase transition when the axion domain wall undergoes an unchecked collapse due to the tension in the wall. If a large number of quarks is trapped inside the bulk of a closed axion domain wall, the collapse stops due to the internal Fermi pressure. In this case the system in the bulk, may reach the critical density when it undergoes a phase transition to a color superconducting phase with the ground state being the quark condensate, similar to the Cooper pairs in BCS theory. If this happens, the new state of matter representing the diquark condensate with a large baryon number $B \sim 10^{32}$ becomes a stable soliton-like configuration. Consequently, it may serve as a novel cold dark matter candidate.Comment: Title changed. Two figures and Appendix added. Part on baryogenesis is removed and posted as a separate paper hep-ph/030908

Supersymmetric Thermalization and Quasi-Thermal Universe: Consequences for Gravitinos and Leptogenesis

Motivated by our earlier paper \cite{am}, we discuss how the infamous gravitino problem has a natural built in solution within supersymmetry. Supersymmetry allows a large number of flat directions made up of {\it gauge invariant} combinations of squarks and sleptons. Out of many at least {\it one} generically obtains a large vacuum expectation value during inflation. Gauge bosons and Gauginos then obtain large masses by virtue of the Higgs mechanism. This makes the rate of thermalization after the end of inflation very small and as a result the Universe enters a {\it quasi-thermal phase} after the inflaton has completely decayed. A full thermal equilibrium is generically established much later on when the flat direction expectation value has substantially decareased. This results in low reheat temperatures, i.e., $T_{\rm R}\sim {\cal O}({\rm TeV})$, which are compatible with the stringent bounds arising from the big bang nucleosynthesis. There are two very important implications: the production of gravitinos and generation of a baryonic asymmetry via leptogenesis during the quasi-thermal phase. In both the cases the abundances depend not only on an effective temperature of the quasi-thermal phase (which could be higher, i.e., $T\gg T_{\rm R}$), but also on the state of equilibrium in the reheat plasma. We show that there is no ``thermal gravitino problem'' at all within supersymmetry and we stress on a need of a new paradigm based on a ``quasi-thermal leptogenesis'', because in the bulk of the parameter space the {\it old} thermal leptogenesis cannot account for the observed baryon asymmetry.Comment: 53 pages. Final version published in JCA

Effective Field Theory Approach to String Gas Cosmology

We derive the 4D low energy effective field theory for a closed string gas on a time dependent FRW background. We examine the solutions and find that although the Brandenberger-Vafa mechanism at late times no longer leads to radion stabilization, the radion rolls slowly enough that the scenario is still of interest. In particular, we find a simple example of the string inspired dark matter recently proposed by Gubser and Peebles.Comment: 19 pages, 2 figures, comments adde

Constraints on Supersymmetric Grand Unified Theories from Cosmology

Within the context of SUSY GUTs, cosmic strings are generically formed at the end of hybrid inflation. However, the WMAP CMB measurements strongly constrain the possible cosmic strings contribution to the angular power spectrum of anisotropies. We investigate the parameter space of SUSY hybrid (F- and D- term) inflation, to get the conditions under which theoretical predictions are in agreement with data. The predictions of F-term inflation are in agreement with data, only if the superpotential coupling $\kappa$ is small. In particular, for SUSY SO(10), the upper bound is \kappa\lsim 7\times 10^{-7}. This fine tuning problem can be lifted if we employ the curvaton mechanism, in which case \kappa\lsim 8\times 10^{-3}; higher values are not allowed by the gravitino constraint. The constraint on $\kappa$ is equivalent to a constraint on the SSB mass scale $M$, namely M \lsim 2\times 10^{15} GeV. The study of D-term inflation shows that the inflaton field is of the order of the Planck scale; one should therefore consider SUGRA. We find that the cosmic strings contribution to the CMB anisotropies is not constant, but it is strongly dependent on the gauge coupling $g$ and on the superpotential coupling $\lambda$. We obtain g\lsim 2\times 10^{-2} and \lambda \lsim 3\times 10^{-5}. SUGRA corrections induce also a lower limit for $\lambda$. Equivalently, the Fayet-Iliopoulos term $\xi$ must satisfy \sqrt\xi \lsim 2\times 10^{15} GeV. This constraint holds for all allowed values of $g$.Comment: 32 pages, 7 figures. To match published versio