766 research outputs found
Inflation with
We discuss various models of inflationary universe with . A
homogeneous universe with may appear due to creation of the
universe "from nothing" in the theories where the effective potential becomes
very steep at large , or in the theories where the inflaton field
nonminimally couples to gravity. Inflation with generally requires
intermediate first order phase transition with the bubble formation, and with a
second stage of inflation inside the bubble. It is possible to realize this
scenario in the context of a theory of one scalar field, but typically it
requires artificially bent effective potentials and/or nonminimal kinetic
terms. It is much easier to obtain an open universe in the models involving two
scalar fields. However, these models have their own specific problems. We
propose three different models of this type which can describe an open
homogeneous inflationary universe.Comment: 29 pages, LaTeX, parameters of one of the models are slightly
modifie
Particle Production and Gravitino Abundance after Inflation
Thermal history after inflation is studied in a chaotic inflation model with
supersymmetric couplings of the inflaton to matter fields. Time evolution
equation is solved in a formalism that incorporates both the back reaction of
particle production and the cosmological expansion. The effect of the
parametric resonance gives rise to a rapid initial phase of the inflaton decay
followed by a slow stage of the Born term decay. Thermalization takes place
immediately after the first explosive stage for a medium strength of the
coupling among created particles. As an application we calculate time evolution
of the gravitino abundance that is produced by ordinary particles directly
created from the inflaton decay, which typically results in much more enhanced
yield than what a naive estimate based on the Born term would suggest.Comment: 23 pages + 13 figure
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
TASI Lectures on the Cosmological Constant
The energy density of the vacuum, Lambda, is at least 60 orders of magnitude
smaller than several known contributions to it. Approaches to this problem are
tightly constrained by data ranging from elementary observations to precision
experiments. Absent overwhelming evidence to the contrary, dark energy can only
be interpreted as vacuum energy, so the venerable assumption that Lambda=0
conflicts with observation. The possibility remains that Lambda is
fundamentally variable, though constant over large spacetime regions. This can
explain the observed value, but only in a theory satisfying a number of
restrictive kinematic and dynamical conditions. String theory offers a concrete
realization through its landscape of metastable vacua.Comment: 39 pages, 3 figure
Inflation with a constant ratio of scalar and tensor perturbation amplitudes
The single scalar field inflationary models that lead to scalar and tensor
perturbation spectra with amplitudes varying in direct proportion to one
another are reconstructed by solving the Stewart-Lyth inverse problem to
next-to-leading order in the slow-roll approximation.
The potentials asymptote at high energies to an exponential form,
corresponding to power law inflation, but diverge from this model at low
energies, indicating that power law inflation is a repellor in this case. This
feature implies that a fine-tuning of initial conditions is required if such
models are to reproduce the observations. The required initial conditions might
be set through the eternal inflation mechanism.
If this is the case, it will imply that the spectral indices must be nearly
constant, making the underlying model observationally indistinguishable from
power law inflation.Comment: 20 pages, 7 figures. Major changes to the Introduction following
referee's comments. One figure added. Some other minor changes. No conclusion
was modifie
The non-forward BFKL amplitude and rapidity gap physics
We discuss the BFKL approach to processes with large momentum transferred
through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward
parton-parton elastic scattering amplitude at large , is extended to include
higher conformal spins. The new contributions are found to decrease with
increasing energy, as follows from the gluon reggeisation phenomenon, and to
vanish for asymptotically high energies. However, at moderate energies and high
, the higher conformal spins dominate the amplitude. We illustrate the
effects by studying the production of two high jets separated by a
rapidity gap at HERA energies. In a simplified framework, we find excellent
agreement with the HERA photoproduction data once we incorporate the rapidity
gap survival probability against soft rescattering effects. We emphasize that
measurements of the analogous process in electroproduction may probe different
summations over conformal spins.Comment: Latex, 14 pages, 3 figures; the final version to appear in Phys.
Lett. B; a short discussion of the Tevatron data added; a previously missing
factor of i^n introduced in eq. (13
Dynamical model of sequential spatial memory: winnerless competition of patterns
We introduce a new biologically-motivated model of sequential spatial memory
which is based on the principle of winnerless competition (WLC). We implement
this mechanism in a two-layer neural network structure and present the learning
dynamics which leads to the formation of a WLC network. After learning, the
system is capable of associative retrieval of pre-recorded sequences of spatial
patterns.Comment: 4 pages, submitted to PR
Dynamics of tachyonic preheating after hybrid inflation
We study the instability of a scalar field at the end of hybrid inflation,
using both analytical techniques and numerical simulations. We improve previous
studies by taking the inflaton field fully into account, and show that the
range of unstable modes depends sensitively on the velocity of the inflaton
field, and thereby on the Hubble rate, at the end of inflation. If topological
defects are formed, their number density is determined by the shortest unstable
wavelength. Finally, we show that the oscillations of the inflaton field
amplify the inhomogeneities in the energy density, leading to local symmetry
restoration and faster thermalization. We believe this explains why tachyonic
preheating is so effective in transferring energy away from the inflaton zero
mode.Comment: 12 pages, 10 figures, REVTeX. Minor changes, some references added.
To appear in PR
Is nonperturbative inflatino production during preheating a real threat to cosmology?
We discuss toy models where supersymmetry is broken due to non-vanishing
time-varying vacuum expectation value of the inflaton field during preheating.
We discuss the production of inflatino the superpartner of inflaton due to
vacuum fluctuations and then we argue that they do not survive until
nucleosynthesis and decay along with the inflaton to produce a thermal bath
after preheating. Thus the only relevant remnant is the helicity \pm 3/2
gravitinos which can genuinely cause problem to nucleosynthesis.Comment: 10 pages, Updates to match the accepted version in Phys. Rev.
Leptoquark Contribution to the Higgs Boson Production at the LHC Collider
In this report we study how a light-scalar leptoquark could affect the Higgs
boson production cross-section at the LHC collider. We construct the most
general renormalizable and gauge invariant effective Lagrangian involving the
standard model particles and a scalar, isoscalar leptoquark, \eta.
The total cross-section for pp -> H+X is then calculated for different values
of the unknown parameters \lambda_eta, m_eta and m_H.(Here \lambda_eta is the
coupling associated with the Higgs-leptoquark interaction.)
We find that if \lambda_eta is moderately large and m_eta is around a few
hundred GeV, then the cross-section is significantly larger than the standard
model value.Comment: 9 pages, 4 postscript figure
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