3,509 research outputs found
Massive spin zero fields in cosmology and the tail-free property
Fields of spin satisfying wave equations in a curved space obey
the Huygens principle under certain conditions clarified by a known theorem.
Here this theorem is generalized to spin zero and applied to an inflaton field
in de Sitter-like space, showing that tails of scalar radiation are an
unavoidable physical feature. Requiring the absence of tails, on the contrary,
necessarily implies an unnatural tuning between cosmological constant, scalar
field mass, and coupling constant to the curvature.Comment: To appear in "Cosmology and Quantum Vacuum", special issue of
Symmetry edited by E. Elizald
Huygens' Principle for the Klein-Gordon equation in the de Sitter spacetime
In this article we prove that the Klein-Gordon equation in the de Sitter
spacetime obeys the Huygens' principle only if the physical mass of the
scalar field and the dimension of the spatial variable are tied by
the equation . Moreover, we define the incomplete Huygens'
principle, which is the Huygens' principle restricted to the vanishing second
initial datum, and then reveal that the massless scalar field in the de Sitter
spacetime obeys the incomplete Huygens' principle and does not obey the
Huygens' principle, for the dimensions , only. Thus, in the de Sitter
spacetime the existence of two different scalar fields (in fact, with m=0 and
), which obey incomplete Huygens' principle, is equivalent to
the condition (in fact, the spatial dimension of the physical world). For
these two values of the mass are the endpoints of the so-called in
quantum field theory the Higuchi bound. The value of the
physical mass allows us also to obtain complete asymptotic expansion of the
solution for the large time. Keywords: Huygens' Principle; Klein-Gordon
Equation; de Sitter spacetime; Higuchi Boun
Semilinear Hyperbolic Equations in Curved Spacetime
This is a survey of the author's recent work rather than a broad survey of
the literature. The survey is concerned with the global in time solutions of
the Cauchy problem for matter waves propagating in the curved spacetimes, which
can be, in particular, modeled by cosmological models. We examine the global in
time solutions of some class of semililear hyperbolic equations, such as the
Klein-Gordon equation, which includes the Higgs boson equation in the Minkowski
spacetime, de Sitter spacetime, and Einstein & de Sitter spacetime. The crucial
tool for the obtaining those results is a new approach suggested by the author
based on the integral transform with the kernel containing the hypergeometric
function.\\ {\bf Mathematics Subject Classification (2010):} Primary 35L71,
35L53; Secondary 81T20, 35C15.\\ {\bf Keywords:} \small {de Sitter spacetime;
Klein-Gordon equation; Global solutions; Huygens' principle; Higuchi bound}Comment: arXiv admin note: text overlap with arXiv:1206.023
CMB-S4 Science Book, First Edition
This book lays out the scientific goals to be addressed by the
next-generation ground-based cosmic microwave background experiment, CMB-S4,
envisioned to consist of dedicated telescopes at the South Pole, the high
Chilean Atacama plateau and possibly a northern hemisphere site, all equipped
with new superconducting cameras. CMB-S4 will dramatically advance cosmological
studies by crossing critical thresholds in the search for the B-mode
polarization signature of primordial gravitational waves, in the determination
of the number and masses of the neutrinos, in the search for evidence of new
light relics, in constraining the nature of dark energy, and in testing general
relativity on large scales
Constraining Dynamical Dark Energy Models through the Abundance of High-Redshift Supermassive Black Holes
We compute the number density of massive Black Holes (BHs) at the centre of
galaxies at z=6 in different Dynamical Dark Energy (DDE) cosmologies, and
compare it with existing observational lower limits, to derive constraints on
the evolution of the Dark Energy equation of state parameter w. Our approach
only assumes the canonical scenario for structure formation from the collapse
of overdense regions of the Dark Matter dominated primordial density field on
progressively larger scales; the Black Hole accretion and merging rate have
been maximized in the computation so as to obtain robust constraints on w and
on its look-back time derivative w_a. Our results provide independent
constraints complementary to those obtained by combining Supernovae, Cosmic
Microwave Background and Baryonic Acoustic Oscillations; while the latter
concern combinations of w_0 and w_a leaving the time evolution of the state
parameter w_a highly unconstrained, the BH abundance mainly provide upper
limits on w_a, only weakly depending on w_0. Combined with the existing
constraints, our results significantly restrict the allowed region in DDE
parameter space, ruling out DDE models not providing cosmic time and fast
growth factor large enough to allow for the building up of the observed
abundance of BHs; in particular, models with -1.2 \leq w_0 \leq -1 and positive
redshift evolution w_a > 0.8 - completely consistent with previous constraints
- are strongly disfavoured by our independent constraints from BH abundance.
Such range of parameters corresponds to "Quintom" DDE models, with w crossing
-1 starting from larger values.Comment: 19 pages, 6 figures, accepted to MNRA
- …