New shifted hybrid inflation

A new shifted hybrid inflationary scenario is introduced which, in contrast to the older one, relies only on renormalizable superpotential terms. This scenario is automatically realized in a concrete extension of the "minimal" supersymmetric Pati-Salam model which naturally leads to a moderate violation of Yukawa unification so that, for mu>0, the predicted b-quark mass is acceptable even with universal boundary conditions. It is shown that this extended model possesses a classically flat "shifted" trajectory which acquires a slope via one-loop radiative corrections and can be used as inflationary path. The constraints from the cosmic background explorer can be met with natural values of the relevant parameters. Also, there is no disastrous production of magnetic monopoles after inflation since the Pati-Salam gauge group is already broken on the "shifted" path. The relevant part of inflation takes place at values of the inflaton field which are not much smaller than the "reduced" Planck scale and, thus, supergravity corrections could easily invalidate inflation. It is, however, shown that inflation can be kept intact provided that an extra gauge singlet with a superheavy vacuum expectation value, which originates from D-terms, is introduced and a specific form of the Kaehler potential is used. Moreover, it is found that, although the supergravity corrections are sizable, the constraints from the cosmic background explorer can again be met by readjusting the values of the parameters which were obtained with global supersymmetry.Comment: 18 pages including 1 figure, uses JHEP3.cls, minor corrections, version to appear in JHE

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

Genericity of Cosmic Strings Formation in SUSY GUTs

The idea of GUT implies that the universe went through a series of phase transitions during which topological defects are expected to form. We investigate here the genericity of cosmic strings formation in realistic SUSY GUTs models. We conclude that all acceptable symmetry breaking schemes produce cosmic strings after the last inflationary phase. Generically, as they form at the end of inflation, they have a mass of order of the GUT scale. Since cosmological data coming from CMB measurements do not show evidence for such strings, they constrain GUT scale physics.Comment: 4 pages, talk at the XXXIX Rencontres de Moriond (La Thuile, March 2004), to appear in the proceeding

Confronting hybrid inflation in supergravity with CMB data

$F$-term GUT inflation coupled to N=1 Supergravity is confronted with CMB data. Corrections to the string mass-per-unit-length away from the Bogomolny limit are taken into account. We find that a superpotential coupling 10^{-7}/\mcN \lesssim \kappa \lesssim 10^{-2}/\mcN, with \mcN the dimension of the Higgs-representation, is still compatible with the data. The parameter space is enlarged in warm inflation, as well as in the curvaton and inhomogeneous reheat scenario. $F$-strings formed at the end of $P$-term inflation are also considered. Because these strings satisfy the Bogomolny bound the bounds are stronger: the gauge coupling is constrained to the range $10^{-7} < g <10^{-4}$.Comment: 36 pages, 15 figure

Non-thermal Production of Neutralino Cold Dark Matter from Cosmic String Decays

We propose a mechanism of nonthermal production of a neutralino cold dark matter particle, $\chi$, from the decay of cosmic strings which form from the spontaneous breaking of a U(1) gauge symmetry, such as $U_{B-L}(1)$, in an extension of the minimal supersymmetric standard model (MSSM). By explicit calculation, we point out that with a symmetry breaking scale $\eta$ of around $10^8$ GeV, the decay of cosmic strings can give rise to $\Omega_\chi \simeq 1$. This gives a new constraint on supersymmetric models. For example, the dark matter produced from strings will overclose the universe if $\eta$ is near the electroweak symmetry breaking scale. To be consistent with $\Omega_\chi \leq 1$, the mass of the new U(1) gauge boson must be much larger than the Fermi scale which makes it unobservable in upcoming accelerator experiments. In a supersymmetric model with an extra $U_{B-L}(1)$ symmetry, the requirement of $\Omega_\chi \leq 1$ puts an upper bound on the neutrino mass of about $30 eV$ provided neutrino masses are generated by the see-saw mechanism.Comment: 4 pages, uses Revtex, 1 figur