705 research outputs found
"Exotic" quantum effects in the laboratory?
This Article provides a brief (non-exhaustive) review of some recent
developments regarding the theoretical and possibly experimental study of
"exotic" quantum effects in the laboratory with special emphasis on
cosmological particle creation, Hawking radiation, and the Unruh effect.Comment: 5 page
Large-scale Perturbations from the Waterfall Field in Hybrid Inflation
We estimate large-scale curvature perturbations from isocurvature
fluctuations in the waterfall field during hybrid inflation, in addition to the
usual inflaton field perturbations. The tachyonic instability at the end of
inflation leads to an explosive growth of super-Hubble scale perturbations, but
they retain the steep blue spectrum characteristic of vacuum fluctuations in a
massive field during inflation. The power spectrum thus peaks around the
Hubble-horizon scale at the end of inflation. We extend the usual delta-N
formalism to include the essential role of these small fluctuations when
estimating the large-scale curvature perturbation. The resulting curvature
perturbation due to fluctuations in the waterfall field is second-order and the
spectrum is expected to be of order 10^{-54} on cosmological scales.Comment: 10 pages, 4 figures; v2 comments added on application of delta-N
formalism including Hubble scale fluctuation
Gravitational Radiation from Preheating with Many Fields
Parametric resonances provide a mechanism by which particles can be created
just after inflation. Thus far, attention has focused on a single or many
inflaton fields coupled to a single scalar field. However, generically we
expect the inflaton to couple to many other relativistic degrees of freedom
present in the early universe. Using simulations in an expanding
Friedmann-Lema\^itre-Robertson-Walker spacetime, in this paper we show how
preheating is affected by the addition of multiple fields coupled to the
inflaton. We focus our attention on gravitational wave production--an important
potential observational signature of the preheating stage. We find that
preheating and its gravitational wave signature is robust to the coupling of
the inflaton to more matter fields.Comment: 7 pages, 8 figures, v2 submission version, thank you for comments
Quantum-to-classical Transition of Cosmological Perturbations for Non-vacuum Initial States
Transition from quantum to semiclassical behaviour and loss of quantum
coherence for inhomogeneous perturbations generated from a non-vacuum initial
state in the early Universe is considered in the Heisenberg and the
Schr\"odinger representations, as well as using the Wigner function. We show
explicitly that these three approaches lead to the same prediction in the limit
of large squeezing (i.e. when the squeezing parameter ): each
two-modes quantum state (k, -k) of these perturbations is equivalent to a
classical perturbation that has a stochastic amplitude, obeying a non-gaussian
statistics which depends on the initial state, and that belongs to the
quasi-isotropic mode (i.e. it possesses a fixed phase). The Wigner function is
not everywhere positive for any finite , hence its interpretation as a
classical distribution function in phase space is impossible without some
coarse graining procedure. However, this does not affect the transition to
semiclassical behaviour since the Wigner function becomes concentrated near a
classical trajectory in phase space when even without coarse
graining. Deviations of the statistics of the perturbations in real space from
a Gaussian one lie below the cosmic variance level for the N-particles initial
states with N=N(|k|) but may be observable for other initial states without
statistical isotropy or with correlations between different k modes. As a way
to look for this effect, it is proposed to measure the kurtosis of the angular
fluctuations of the cosmic microwave background temperature.Comment: LaTeX (28 pages),+2 eps figure
Optimal dataset combining in f_nl constraints from large scale structure in an idealised case
We consider the problem of optimal weighting of tracers of structure for the
purpose of constraining the non-Gaussianity parameter f_NL. We work within the
Fisher matrix formalism expanded around fiducial model with f_NL=0 and make
several simplifying assumptions. By slicing a general sample into infinitely
many samples with different biases, we derive the analytic expression for the
relevant Fisher matrix element. We next consider weighting schemes that
construct two effective samples from a single sample of tracers with a
continuously varying bias. We show that a particularly simple ansatz for
weighting functions can recover all information about f_NL in the initial
sample that is recoverable using a given bias observable and that simple
division into two equal samples is considerably suboptimal when sampling of
modes is good, but only marginally suboptimal in the limit where Poisson errors
dominate.Comment: 6 pages, 5 figures; v2: comment on weighting for PS determination,
fixed a couple of typos; v3: revised, matches version accepted by JCA
Graviton emission from a higher-dimensional black hole
We discuss the graviton absorption probability (greybody factor) and the
cross-section of a higher-dimensional Schwarzschild black hole (BH). We are
motivated by the suggestion that a great many BHs may be produced at the LHC
and bearing this fact in mind, for simplicity, we shall investigate the
intermediate energy regime for a static Schwarzschild BH. That is, for
, where is the mass of the black hole and
is the energy of the emitted gravitons in -dimensions. To find
easily tractable solutions we work in the limit , where is the
angular momentum quantum number of the graviton.Comment: 10 pages, 8 figures, references added, typos corrected. Graviton
degeneracy factor included; main results remain unchange
Inflation and non-minimal scalar-curvature coupling in gravity and supergravity
Inflationary slow-roll dynamics in Einstein gravity with a non-minimal
scalar-curvature coupling can be equivalent to that in the certain f(R) gravity
theory. We review the correspondence and extend it to N=1 supergravity. The
non-minimal coupling in supergravity is rewritten in terms of the standard
(`minimal') N=1 matter-coupled supergravity by using curved superspace. The
established equivalence between two different inflationary theories means the
same inflaton scalar potential, and does not imply the same post-inflationary
dynamics and reheating.Comment: 18 pages, no figures, LaTeX. minor changes, references added, the
version published in JCAP. arXiv admin note: substantial text overlap with
arXiv:1201.2239, arXiv:1011.024
Non-canonical generalizations of slow-roll inflation models
We consider non-canonical generalizations of two classes of simple
single-field inflation models. First, we study the non-canonical version of
"ultra-slow roll" inflation, which is a class of inflation models for which
quantum modes do not freeze at horizon crossing, but instead evolve rapidly on
superhorizon scales. Second, we consider the non-canonical generalization of
the simplest "chaotic" inflation scenario, with a potential dominated by a
quartic (mass) term for the inflaton. We find a class of related non-canonical
solutions with polynomial potentials, but with varying speed of sound. These
solutions are characterized by a constant field velocity, and we dub such
models {\it isokinetic} inflation. As in the canonical limit, isokinetic
inflation has a slightly red-tilted power spectrum, consistent with current
data. Unlike the canonical case, however, these models can have an arbitrarily
small tensor/scalar ratio. Of particular interest is that isokinetic inflation
is marked by a correlation between the tensor/scalar ratio and the amplitude of
non-Gaussianity such that parameter regimes with small tensor/scalar ratio have
{\it large} associated non-Gaussianity, which is a distinct observational
signature.Comment: 12 pages, 3 figures, LaTeX; V2: version submitted to JCAP. References
adde
A note on the moduli-induced gravitino problem
The cosmological moduli problem has been recently reconsidered. Papers [1,2]
show that even heavy moduli (m_\phi > 10^5 GeV) can be a problem for cosmology
if a branching ratio of the modulus into gravitini is large. In this paper, we
discuss the tachyonic decay of moduli into the Standard Model's degrees of
freedom, e.g. Higgs particles, as a resolution to the moduli-induced gravitino
problem. Rough estimates on model dependent parameters set a lower bound on the
allowed moduli at around 10^8 ~ 10^9 GeV.Comment: 6 pages, references added, identical to the published versio
Cosmological density perturbations from conformal scalar field: infrared properties and statistical anisotropy
We consider a scenario in which primordial scalar perturbations are generated
when complex conformal scalar field rolls down its negative quartic potential.
Initially, these are the perturbations of the phase of this field; they are
converted into the adiabatic perturbations at a later stage. A potentially
dangerous feature of this scenario is the existence of perturbations in the
radial field direction, which have red power spectrum. We show, however, that
to the linear order in the small parameter - the quartic self-coupling - the
infrared effects are completely harmless, as they can be absorbed into field
redefinition. We then evaluate the statistical anisotropy inherent in the model
due to the existence of the long-ranged radial perturbations. To the linear
order in the quartic self-coupling the statistical anisotropy is free of the
infrared effects. The latter show up at the quadratic order in the
self-coupling and result in the mild (logarithmic) enhancement of the
corresponding contribution to the statistical anisotropy. The resulting
statistical anisotropy is a combination of a larger term which, however, decays
as momentum increases, and a smaller term which is independent of momentum.Comment: 19 pages, 2 figures. Journal version, typos corrected, subsection
adde
- …