130 research outputs found
How to remedy the eta-problem of SUSY GUT hybrid inflation via vector backreaction
It is shown that, in supergravity models of inflation where the gauge kinetic
function of a gauge field is modulated by the inflaton, we can obtain a new
inflationary attractor solution, in which the roll-over of the inflaton suffers
additional impedance due to the vector field backreaction. As a result,
directions of the scalar potential which, due to strong Kaehler corrections,
become too steep and curved to normally support slow-roll inflation can now
naturally do so. This solves the infamous eta-problem of inflation in
supergravity and also keeps the spectral index of the curvature perturbation
mildly red despite eta of order unity. This mechanism is applied to a model of
hybrid inflation in supergravity with a generic Kaehler potential. The spectral
index of the curvature perturbation is found to be 0.97 - 0.98, in excellent
agreement with data. The gauge field can act as vector curvaton generating
statistical anisotropy in the curvature perturbation. However, this anisotropy
could be possibly observable only if the gauge coupling constant is unnaturally
small.Comment: 10 pages, talk given at the International Workshop on Grand Unified
Theories (GUT2012), Yukawa Institute for Theoretical Physics, Kyoto
University, Kyoto, Japan, March 15-17, 2012 (to appear in the proceedings
The Standard-smooth Variant of Hybrid Inflation
We consider the extension of the supersymmetric Pati-Salam model introduced
in order to solve the b-quark mass problem in supersymmetric theories with
Yukawa unification, universal boundary conditions and mu>0. This model
naturally leads to the new shifted and new smooth hybrid inflation scenarios,
which, however, yield, in minimal supergravity, too large values of the
spectral index n_s. We show that this problem can also be resolved within the
same model by a two-stage inflationary scenario based only on renormalizable
superpotential interactions. The first stage is of the standard and the second
of the new smooth hybrid type. The cosmological scales exit the horizon during
the first stage of inflation and acceptable n_s's can be achieved by
restricting the number of e-foldings of our present horizon during this
inflationary stage. The additional e-foldings needed for solving the horizon
and flatness problems are naturally provided by the second stage of inflation.
Monopoles are formed at the end of the first stage of inflation and are,
subsequently, diluted by the second stage of inflation so that their density in
the present universe is utterly negligible.Comment: 10 pages including 1 figure, uses aipproc.cls, talk given at the
BUE,CTP International Conference on Neutrino Physics in the LHC Era, Luxor,
Egypt, 15-19 November 2009 (to appear in the proceedings
New smooth hybrid inflation
We consider the extension of the supersymmetric Pati-Salam model which solves
the b-quark mass problem of supersymmetric grand unified models with exact
Yukawa unification and universal boundary conditions and leads to the so-called
new shifted hybrid inflationary scenario. We show that this model can also lead
to a new version of smooth hybrid inflation based only on renormalizable
interactions provided that a particular parameter of its superpotential is
somewhat small. The potential possesses valleys of minima with classical
inclination, which can be used as inflationary paths. The model is consistent
with the fitting of the three-year Wilkinson microwave anisotropy probe data by
the standard power-law cosmological model with cold dark matter and a
cosmological constant. In particular, the spectral index turns out to be
adequately small so that it is compatible with the data. Moreover, the
Pati-Salam gauge group is broken to the standard model gauge group during
inflation and, thus, no monopoles are formed at the end of inflation.
Supergravity corrections based on a non-minimal Kaehler potential with a
convenient choice of a sign keep the spectral index comfortably within the
allowed range without generating maxima and minima of the potential on the
inflationary path. So, unnatural restrictions on the initial conditions for
inflation can be avoided.Comment: 15 pages including 5 figures, uses Revtex, version to appear in PR
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
Standard-smooth hybrid inflation
We consider the extended supersymmetric Pati-Salam model which, for mu>0 and
universal boundary conditions, succeeds to yield experimentally acceptable
b-quark masses by moderately violating Yukawa unification. It is known that
this model can lead to new shifted or new smooth hybrid inflation. We show that
a successful two-stage inflationary scenario can be realized within this model
based only on renormalizable superpotential interactions. The cosmological
scales exit the horizon during the first stage of inflation, which is of the
standard hybrid type and takes place along the trivial flat direction with the
inflaton driven by radiative corrections. Spectral indices compatible with the
recent data can be achieved in global supersymmetry or minimal supergravity by
restricting the number of e-foldings of our present horizon during the first
inflationary stage. The additional e-foldings needed for solving the horizon
and flatness problems are naturally provided by a second stage of inflation,
which occurs mainly along the built-in new smooth hybrid inflationary path
appearing right after the destabilization of the trivial flat direction at its
critical point. Monopoles are formed at the end of the first stage of inflation
and are, subsequently, diluted by the second stage of inflation to become
utterly negligible in the present universe for almost all (for all) the allowed
values of the parameters in the case of global supersymmetry (minimal
supergravity).Comment: 11 pages including 2 figures, uses Revtex, version to appear in Phys.
Rev.
Dissipative breathers in rf SQUID metamaterials
The existence and stability of dissipative breathers in rf SQUID
(Superconducting Quantum Interference Device) arrays is investigated
numerically. In such arrays, the nonlinearity which is intrinsic to each SQUID,
along with the weak magnetic coupling of each SQUID to its nearest neighbors,
result in the formation of discrete breathers. We analyze several discrete
breather excitations in rf SQUID arrays driven by alternating flux sources in
the presence of losses. The delicate balance between internal power losses and
input power, results in the formation of dissipative discrete breather (DDB)
structures up to relatively large coupling parameters. It is shown that DDBs
may locally alter the magnetic response of an rf SQUID array from paramagnetic
to diamagnetic or vice versa.Comment: 5 pages, 4 figure
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