5,168 research outputs found
Inflation with blowing-up solution of cosmological constant problem
The cosmological constant problem is how one chooses, without fine-tuning,
one singular point for the 4D cosmological constant. We argue
that some recently discovered {\it weak self-tuning} solutions can be viewed as
blowing-up this one point into a band of some parameter. These weak self-tuning
solutions may have a virtue that only de Sitter space solutions are allowed
outside this band, allowing an inflationary period. We adopt the hybrid
inflation at the brane to exit from this inflationary phase and to enter into
the standard Big Bang cosmology.Comment: LaTeX file of 20 pages including 2 eps figure
String compactification, QCD axion and axion-photon-photon coupling
It is pointed out that there exist a few problems to be overcome toward an
observable sub-eV QCD axion in superstring compactification. We give a general
expression for the axion decay constant. For a large domain wall number
, the axion decay constant can be substantially lowered from a generic
value of a scalar singlet VEV. The Yukawa coupling structure in the recent
model is studied completely, including the needed nonrenormalizable
terms toward realistic quark and lepton masses. In this model we find an
approximate global symmetry and vacuum so that a QCD axion results but its
decay constant is at the GUT scale. The axion-photon-photon coupling is
calculated for a realistic vacuum satisfying the quark and lepton mass matrix
conditions. It is the first time calculation of in
realistic string compactifications: .Comment: 33 pages, 2 figures, JHEP format, some errors in the superpotential
couplings are corrected and the following discussions are changed
correspondingl
Einstein Gravity on a Brane in 5D Non-compact Flat Spacetime -DGP model revisited-
We revisit the 5D gravity model by Dvali, Gabadadze, and Porrati (DGP).
Within their framework it was shown that even in 5D non-compact Minkowski space
, the Newtonian gravity can emerge on a brane at short distances by
introducing a brane-localized 4D Einstein-Hilbert term
in the action. Based on this idea,
we construct simple setups in which graviton standing waves can arise, and we
introduce brane-localized derivative terms as a correction to
. We show that the gravity potential
of brane matter becomes at {\it long} distances, because the
brane-localized derivative terms allow only a smooth graviton wave function
near the brane. Since the bulk gravity coupling may be arbitrarily small,
strongly interacting modes from the 5D graviton do not appear. We note that the
brane metric utilized to construct
can be relatively different from the bulk metric by a conformal factor, and
show that the graviton tensor structure that the 4D Einstein gravity predicts
are reproduced in DGP type models.Comment: 1+12 pages, no figure, to appear in JHE
Axionic dark energy and a composite QCD axion
We discuss the idea that the model-independent (MI) axion of string theory is
the source of quintessential dark energy. The scenario is completed with a
composite QCD axion from hidden sector squark condensation that could serve as
dark matter candidate. The mechanism relies on the fact that the hidden sector
anomaly contribution to the composite axion is much smaller than the QCD
anomaly term. This intuitively surprising scenario is based on the fact that
below the hidden sector scale there are many light hidden sector
quarks. Simply, by counting engineering dimensions the hidden sector instanton
potential can be made negligible compared to the QCD anomaly term.Comment: 9 pages, 7 figure
Optical sum rule violation, superfluid weight and condensation energy in the cuprates
The model of hole superconductivity predicts that the superfluid weight in
the zero-frequency -function in the optical conductivity has an
anomalous contribution from high frequencies, due to lowering of the system's
kinetic energy upon entering the superconducting state. The lowering of kinetic
energy, mainly in-plane in origin, accounts for both the condensation energy of
the superconductor as well as an increased potential energy due to larger
Coulomb repulsion in the paired state. It leads to an apparent violation of the
conductivity sum rule, which in the clean limit we predict to be substantially
larger for in-plane than for c-axis conductivity. However, because cuprates are
in the dirty limit for c-axis transport, the sum rule violation is found to be
greatly enhanced in the c-direction. The model predicts the sum rule violation
to be largest in the underdoped regime and to decrease with doping, more
rapidly in the c-direction that in the plane. So far, experiments have detected
sum rule violation in c-axis transport in several cuprates, as well as a
decrease and disappearance of this violation for increasing doping, but no
violation in-plane. We explore the predictions of the model for a wide range of
parameters, both in the absence and in the presence of disorder, and the
relation with current experimental knowledge.Comment: submitted to Phys.Rev.
Axion-photon Couplings in Invisible Axion Models
We reexamine the axion-photon couplings in various invisible axion models
motivated by the recent proposal of using optical interferometry at the ASST
facility in the SSCL to search for axion. We illustrate that the assignment of
charges for the fermion fields plays an important role in
determining the couplings. Several simple non-minimal invisible axion models
with suppressed and enhanced axion-photon couplings are constructed,
respectively. We also discuss the implications of possible new experiments to
detect solar axions by conversion to -rays in a static magnetic apparatus
tracking the sun.Comment: 14 pages, LaTeX fil
When Aggression Is Out of Control: From One-Person to Two-Person Neuropsychology
From a neuropsychological perspective, impulsive aggression and its treatment are usually conceptualized in most research as a closed executive functioning system, as though the behavior was the product of the personâs cerebral functioning only. However, recent studies in social cognitive neuroscience have emphasized the influence of social factors on cognitive processes and cerebral functioning for the development and maintenance of impulsive aggression. This chapter will review studies that highlight the relevance of initiating a shift of paradigm from a one-person-cerebral functioning model to a social interactive-cerebral functioning model of impulsive aggression. First, the influences of an aversive environment on a childâs cognitive processes and executive functioning will be discussed with the aim of explaining the development of impulsive aggressive behaviors in early childhood. Second, we will review studies that have shown how the link between social information processes and executive/inhibitory functioning serve to maintain behaviors. Finally, strengths and weaknesses of existing inhibitory control strategies will be discussed with the intention of proposing some novel ideas that incorporate a two-person neuropsychological approach
Inflationary Cosmology with Five Dimensional SO(10)
We discuss inflationary cosmology in a five dimensional SO(10) model
compactified on , which yields below the compactification scale. The gauge
symmetry is preserved on one of the fixed points, while
``flipped'' is on the other fixed point. Inflation is
associated with breaking, and is implemented through -term scalar
potentials on the two fixed points. A brane-localized Einstein-Hilbert term
allows both branes to have positive tensions during inflation. The scale of
breaking is fixed from measurements to be around
GeV, and the scalar spectral index . The inflaton field
decays into right-handed neutrinos whose subsequent out of equilibrium decay
yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in
PR
Nontrival Cosmological Constant in Brane Worlds with Unorthodox Lagrangians
In self-tuning brane-world models with extra dimensions, large contributions
to the cosmological constant are absorbed into the curvature of extra
dimensions and consistent with flat 4d geometry. In models with conventional
Lagrangians fine-tuning is needed nevertheless to ensure a finite effective
Planck mass. Here, we consider a class of models with non conventional
Lagrangian in which known problems can be avoided. Unfortunately these models
are found to suffer from tachyonic instabilities. An attempt to cure these
instabilities leads to the prediction of a positive cosmological constant,
which in turn needs a fine-tuning to be consistent with observations.Comment: 17 pages, 1 figur
On the thin-shell limit of branes in the presence of Gauss-Bonnet interactions
In this paper we study thick-shell braneworld models in the presence of a
Gauss-Bonnet term. We discuss the peculiarities of the attainment of the
thin-shell limit in this case and compare them with the same situation in
Einstein gravity. We describe the two simplest families of thick-brane models
(parametrized by the shell thickness) one can think of. In the thin-shell
limit, one family is characterized by the constancy of its internal density
profile (a simple structure for the matter sector) and the other by the
constancy of its internal curvature scalar (a simple structure for the
geometric sector). We find that these two families are actually equivalent in
Einstein gravity and that the presence of the Gauss-Bonnet term breaks this
equivalence. In the second case, a shell will always keep some non-trivial
internal structure, either on the matter or on the geometric sectors, even in
the thin-shell limit.Comment: 17 pages, 2 figures, RevTeX 4. Revised version accepted for
publication in Physical Review
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