5,577 research outputs found
False Vacuum Chaotic Inflation: The New Paradigm?
Recent work is reported on inflation model building in the context of
supergravity and superstrings, with special emphasis on False Vacuum (`Hybrid')
Chaotic Inflation. Globally supersymmetric models do not survive in generic
supergravity theories, but fairly simple conditions can be formulated which do
ensure successful supergravity inflation. The conditions are met in some of the
versions of supergravity that emerge from superstrings.Comment: 4 pages, LATEX, LANCASTER-TH 94-1
Inflationary cosmology of the extreme cosmic string
Starting with a study of the cosmological solution to the Einstein equations
for the internal spacetime of an extreme supermassive cosmic string kink, and
by evaluating the probability measure for the formation of such a kink in
semiclassical approximation using a minisuperspace with the appropriate
symmetry, we have found a set of arguments in favor of the claim that the
kinked extreme string can actually be regarded as a unbounded chain of pairs of
Planck- sized universes. Once one such universe pairs is created along a
primordial phase transition at the Planck scale, it undergoes an endless
process of continuous self-regeneration driven by chaotic inflation in each of
the universes forming the pair.Comment: 15 pages, RevTex, to appear in Int. J. Mod. Phys.
Observational tests of inflation with a field derivative coupling to gravity
A field kinetic coupling with the Einstein tensor leads to a gravitationally
enhanced friction during inflation, by which even steep potentials with
theoretically natural model parameters can drive cosmic acceleration. In the
presence of this non-minimal derivative coupling we place observational
constraints on a number of representative inflationary models such as chaotic
inflation, inflation with exponential potentials, natural inflation, and hybrid
inflation. We show that most of the models can be made compatible with the
current observational data mainly due to the suppressed tensor-to-scalar ratio.Comment: 11 pages, 5 figure
First CMB Constraints on the Inflationary Reheating Temperature
We present the first Bayesian constraints on the single field inflationary
reheating era obtained from Cosmic Microwave Background (CMB) data. After
demonstrating that this epoch can be fully characterized by the so-called
reheating parameter, we show that it is constrained by the seven years
Wilkinson Microwave Anisotropies Probe (WMAP7) data for all large and small
field models. An interesting feature of our approach is that it yields lower
bounds on the reheating temperature which can be combined with the upper bounds
associated with gravitinos production. For large field models, we find the
energy scale of reheating to be higher than those probed at the Large Hadron
Collider, Ereh > 17.3 TeV at 95% of confidence. For small field models, we
obtain the two-sigma lower limits Ereh > 890 TeV for a mean equation of state
during reheating = -0.3 and Ereh > 390 GeV for = -0.2. The
physical origin of these constraints is pedagogically explained by means of the
slow-roll approximation. Finally, when marginalizing over all possible
reheating history, the WMAP7 data push massive inflation under pressure (p <
2.2 at 95% of confidence where p is the power index of the large field
potentials) while they slightly favor super-Planckian field expectation values
in the small field models.Comment: 18 pages, 15 figures, uses RevTeX. References added, matches
published versio
Islands in the landscape
The string theory landscape consists of many metastable de Sitter vacua,
populated by eternal inflation. Tunneling between these vacua gives rise to a
dynamical system, which asymptotically settles down to an equilibrium state. We
investigate the effects of sinks to anti-de Sitter space, and show how their
existence can change probabilities in the landscape. Sinks can disturb the
thermal occupation numbers that would otherwise exist in the landscape and may
cause regions that were previously in thermal contact to be divided into
separate, thermally isolated islands.Comment: 31 pages, 8 figure
Inflation without Slow Roll
We draw attention to the possibility that inflation (i.e. accelerated
expansion) might continue after the end of slow roll, during a period of fast
oscillations of the inflaton field \phi . This phenomenon takes place when a
mild non-convexity inequality is satisfied by the potential V(\phi). The
presence of such a period of \phi-oscillation-driven inflation can
substantially modify reheating scenarios.
In some models the effect of these fast oscillations might be imprinted on
the primordial perturbation spectrum at cosmological scales.Comment: 9 pages, Revtex, psfig, 1 figure, minor modifications, references
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An Isocurvature CDM Cosmogony. I. A Worked Example of Evolution Through Inflation
I present a specific worked example of evolution through inflation to the
initial conditions for an isocurvature CDM model for structure formation. The
model invokes three scalar fields, one that drives power law inflation, one
that survives to become the present-day CDM, and one that gives the CDM field a
mass that slowly decreases during inflation and so ``tilts'' the primeval mass
fluctuation spectrum of the CDM. The functional forms for the potentials and
the parameter values that lead to an observationally acceptable model for
structure formation do not seem to be out of line with current ideas about the
physics of the very early universe. I argue in an accompanying paper that the
model offers an acceptable fit to main observational constraints.Comment: 11 pages, 3 postscript figures, uses aas2pp4.st
The Triple-Alpha Process and the Anthropically Allowed Values of the Weak Scale
In multiple-universe models, the constants of nature may have different
values in different universes. Agrawal, Barr, Donoghue and Seckel have pointed
out that the Higgs mass parameter, as the only dimensionful parameter of the
standard model, is of particular interest. By considering a range of values of
this parameter, they showed that the Higgs vacuum expectation value must have a
magnitude less than 5.0 times its observed value, in order for complex
elements, and thus life, to form. In this report, we look at the effects of the
Higgs mass parameter on the triple-alpha process in stars. This process, which
is greatly enhanced by a resonance in Carbon-12, is responsible for virtually
all of the carbon production in the universe. We find that the Higgs vacuum
expectation value must have a magnitude greater than 0.90 times its observed
value in order for an appreciable amount of carbon to form, thus significantly
narrowing the allowed region of Agrawal et al.Comment: 9 pages, 1 figur
The Non-Perturbative Contribution to the Free Energy of Hot SU(N) Gauge Theory
The non-perturbative input necessary for the determination of the part of the weak coupling expansion of the free energy density for
SU(2) and SU(3) gauge theories is estimated. Although the perturbative
information completing the contribution to this order is missing, we give
arguments that the magnetic fluctuations are dominated by screened elementary
magnetic gluons.Comment: Talk presented at LATTICE96(finite temperature) 3 pages Latex2e, 3 ps
figures, 14 k
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