161 research outputs found
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
-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. -strings formed at the end of -term
inflation are also considered. Because these strings satisfy the Bogomolny
bound the bounds are stronger: the gauge coupling is constrained to the range
.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, , from the decay of cosmic strings which form from the
spontaneous breaking of a U(1) gauge symmetry, such as , in an
extension of the minimal supersymmetric standard model (MSSM). By explicit
calculation, we point out that with a symmetry breaking scale of around
GeV, the decay of cosmic strings can give rise to . This gives a new constraint on supersymmetric models. For example, the dark
matter produced from strings will overclose the universe if is near the
electroweak symmetry breaking scale. To be consistent with , 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 symmetry, the requirement of
puts an upper bound on the neutrino mass of about
provided neutrino masses are generated by the see-saw mechanism.Comment: 4 pages, uses Revtex, 1 figur
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