121 research outputs found
Towards Resolution of Hierarchy Problems in a Cosmological Context
A cosmological scenario is proposed, which simultaneously solves the mass
hierarchy and the small dark energy problem. In the present scenario an
effective gravity mass scale (inverse of the Newton's constant) increases
during the inflationary period. The small cosmological constant or the dark
energy density in the present universe is dynamically realized by introducing
two, approximately O(2) symmetric dilatons, taking the fundamental mass scale
at TeV.Comment: 12 pages, no figur
Quantum anti-Zeno effect without wave function reduction
We study the measurement-induced enhancement of the spontaneous decay (called
quantum anti-Zeno effect) for a two-level subsystem, where measurements are
treated as couplings between the excited state and an auxiliary state rather
than the von Neumann's wave function reduction. The photon radiated in a fast
decay of the atom, from the auxiliary state to the excited state, triggers a
quasi-measurement, as opposed to a projection measurement. Our use of the term
"quasi-measurement" refers to a "coupling-based measurement". Such frequent
quasi-measurements result in an exponential decay of the survival probability
of atomic initial state with a photon emission following each
quasi-measurement. Our calculations show that the effective decay rate is of
the same form as the one based on projection measurements. What is more
important, the survival probability of the atomic initial state which is
obtained by tracing over all the photon states is equivalent to the survival
probability of the atomic initial state with a photon emission following each
quasi-measurement to the order under consideration. That is because the
contributions from those states with photon number less than the number of
quasi-measurements originate from higher-order processes.Comment: 7 pages, 3 figure
The Mass, Normalization and Late Time behavior of the Tachyon Field
We study the dynamics of the tachyon field . We derive the mass of the
tachyon as the pole of the propagator which does not coincide with the standard
mass given in the literature in terms of the second derivative of or
. We determine the transformation of the tachyon in order to have a
canonical scalar field . This transformation reduces to the one obtained
for small but it is also valid for large values of . This is
specially interesting for the study of dark energy where . We
also show that the normalized tachyon field is constrained to the
interval where are zeros of the original
potential . This results shows that the field does not know of the
unboundedness of , as suggested for bosonic open string tachyons. Finally
we study the late time behavior of tachyon field using the L'H\^{o}pital rule.Comment: 9 pages, 10 figure
Nonthermal Supermassive Dark Matter
We discuss several cosmological production mechanisms for nonthermal
supermassive dark matter and argue that dark matter may be elementary particles
of mass much greater than the weak scale. Searches for dark matter should not
be limited to weakly interacting particles with mass of the order of the weak
scale, but should extend into the supermassive range as well.Comment: 11 page LaTeX file. No major changes. Version accepted by PR
Cosmic microwave background: polarization and temperature anisotropies from symmetric structures
I consider the case of anisotropies in the Cosmic Microwave Background (CMB)
from one single ordered perturbation source, or seed, existing well before
decoupling between matter and radiation. Such structures could have been left
by high energy symmetries breaking in the early universe.
I focus on the cases of spherical and cylindrical symmetry of the seed. I
give general analytic expressions for the polarization and temperature linear
perturbations, factoring out of the Fourier integral the dependence on the
photon propagation direction and on the geometric coordinates describing the
seed. I show how the CMB perturbations manifestly reflect the symmetries of
their seeds. CMB anisotropies are obtained with a line of sight integration.
This treatment highlights the undulatory properties of the CMB. I show with
numerical examples how the polarization and temperature perturbations propagate
beyond the size of their seeds, reaching the CMB sound horizon at the time
considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy
from a seed intersecting the last scattering surface appears as a series of
temperature and polarization waves surrounding the seed, extending on the scale
of the CMB sound horizon at decoupling, roughly in the sky. Each wave
is characterized by its own value of the CMB perturbation, with the same mean
amplitude of the signal coming from the seed interior.
These waves could allow to distinguish relics from high energy processes of
the early universe from point-like astrophysical sources, because of their
angular extension and amplitude. Also, the marked analogy between polarization
and temperature signals offers cross correlation possibilities for the future
Planck Surveyor observations.Comment: 21 pages, seven postscript figures, final version accepted for
publication in Phys.Rev.
Particle Physics Models of Inflation and the Cosmological Density Perturbation
This is a review of particle-theory models of inflation, and of their
predictions for the primordial density perturbation that is thought to be the
origin of structure in the Universe. It contains mini-reviews of the relevant
observational cosmology, of elementary field theory and of supersymmetry, that
may be of interest in their own right. The spectral index , specifying
the scale-dependence of the spectrum of the curvature perturbation, will be a
powerful discriminator between models, when it is measured by Planck with
accuracy . The usual formula for is derived, as well as
its less familiar extension to the case of a multi-component inflaton; in both
cases the key ingredient is the separate evolution of causally disconnected
regions of the Universe. Primordial gravitational waves will be an even more
powerful discriminator if they are observed, since most models of inflation
predict that they are completely negligible. We treat in detail the new wave of
models, which are firmly rooted in modern particle theory and have
supersymmetry as a crucial ingredient. The review is addressed to both
astrophysicists and particle physicists, and each section is fairly homogeneous
regarding the assumed background knowledge.Comment: 156 pages, after final proof corrections and addition
Inflationary models inducing non-Gaussian metric fluctuations
We construct explicit models of multi-field inflation in which the primordial
metric fluctuations do not necessarily obey Gaussian statistics. These models
are realizations of mechanisms in which non-Gaussianity is first generated by a
light scalar field and then transferred into curvature fluctuations. The
probability distribution functions of the metric perturbation at the end of
inflation are computed. This provides a guideline for designing strategies to
search for non-Gaussian signals in future CMB and large scale structure
surveys.Comment: 4 pages, 7 figure
Tachyonic open inflationary universes
We study one-field open inflationary models in a universe dominated by
tachyon matter. In these scenarios, we determine and characterize the existence
of the Coleman-De Lucia (CDL) instanton. Also, we study the Lorentzian regime,
that is, the period of inflation after tunnelling has occurred.Comment: 13 pages, 7 figures. Accepted by Physics Letters
Moduli Inflation from Dynamical Supersymmetry Breaking
Moduli fields, which parameterize perturbative flat directions of the
potential in supersymmetric theories, are natural candidates to act as
inflatons. An inflationary potential on moduli space can result if the scale of
dynamical SUSY breaking in some sector of the theory is determined by a moduli
dependent coupling. The magnitude of density fluctuations generated during
inflation then depends on the scale of SUSY breaking in this sector. This can
naturally be hierarchically smaller than the Planck scale in a dynamical model,
giving small fluctuations without any fine tuning of parameters. It is also
natural for SUSY to be restored at the minimum of the moduli potential, and to
leave the universe with zero cosmological constant after inflation. Acceptable
reheating can also be achieved in this scenario.Comment: 14 pages, latex, improved discussion of reheating for composite
inflaton
Cosmological perturbations from multi-field inflation in generalized Einstein theories
We study cosmological perturbations generated from quantum fluctuations in
multi-field inflationary scenarios in generalized Einstein theories, taking
both adiabatic and isocurvature modes into account. In the slow-roll
approximation, explicit closed-form long-wave solutions for field and metric
perturbations are obtained by the analysis in the Einstein frame. Since the
evolution of fluctuations depends on specific gravity theories, we make
detailed investigations based on analytic and numerical approaches in four
generalized Einstein theories: the Jordan-Brans-Dicke (JBD) theory, the
Einstein gravity with a non-minimally coupled scalar field, the
higher-dimensional Kaluza-Klein theory, and the theory with a
non-minimally coupled scalar field. We find that solutions obtained in the
slow-roll approximation show good agreement with full numerical results except
around the end of inflation. Due to the presence of isocurvature perturbations,
the gravitational potential and the curvature perturbations
and do not remain constant on super-horizon scales. In particular, we
find that negative non-minimal coupling can lead to strong enhancement of
in both the Einstein and higher derivative gravity, in which case it
is difficult to unambiguously decompose scalar perturbations into adiabatic and
isocurvature modes during the whole stage of inflation.Comment: 23 pages, 5 figures, Accepted for publication in Nuclear Physics B,
some typos are correcte
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