315 research outputs found
Dynamics of Q-Balls in an expanding universe
We analyse the evolution of light Q-balls in a cosmological background, and
find a number of interesting features. For Q-balls formed with a size
comparable to the Hubble radius, we demonstrate that there is no charge
radiation, and that the Q-ball maintains a constant physical radius. Large
expansion rates cause charge migration to the surface of the Q-ball,
corresponding to a non-homogeneous internal rotation frequency. We argue that
this is an important phenomenon as it leads to a large surface charge and
possible fragmentation of the Q-ball. We also explore the deviation of the
Q-ball profile function from the static case. By introducing a parameter
, which is the ratio of the Hubble parameter to the frequency of
oscillation of the Q-ball field, and using solutions to an analytically
approximated equation for the profile function, we determine the dependence of
the new features on the expansion rate. This allows us to gain an understanding
of when they should be considered and when they can be neglected, thereby
placing restrictions on the existence of homogeneous Q-balls in expanding
backgrounds.Comment: 5 pages, 4 figure
Genomic structure and expression of uncoupling protein 2 genes in rainbow trout (Oncorhynchus mykiss)
Background
Uncoupling protein 2 (UCP2) belongs to the superfamily of mitochondrial anion carriers that dissociate the respiratory chain from ATP synthesis. It has been determined that UCP2 plays a role in several physiological processes such as energy expenditure, body weight control and fatty acid metabolism in several vertebrate species. We report the first characterization of UCP2 s in rainbow trout (Oncorhynchus mykiss). Results
Two UCP2 genes were identified in the rainbow trout genome, UCP2A and UCP2B. These genes are 93% similar in their predicted amino acid sequences and display the same genomic structure as other vertebrates (8 exons and 7 introns) spanning 4.2 kb and 3.2 kb, respectively. UCP2A and UCP2B were widely expressed in all tissues of the study with a predominant level in macrophage-rich tissues and reproductive organs. In fry muscle we observed an increase in UCP2B expression in response to fasting and a decrease after refeeding in agreement with previous studies in human, mouse, rat, and marsupials. The converse expression pattern was observed for UCP2A mRNA which decreased during fasting, suggesting different metabolic roles for UCP2A and UCP2B in rainbow trout muscle. Phylogenetic analysis including other genes from the UCP core family located rainbow trout UCP2A and UCP2B with their orthologs and suggested an early divergence of vertebrate UCPs from a common ancestor gene. Conclusion
We characterized two UCP2 genes in rainbow trout with similar genomic structures, amino acid sequences and distribution profiles. These genes appeared to be differentially regulated in response to fasting and refeeding in fry muscle. The genomic organization and phylogeny analysis support the hypothesis of a common ancestry between the vertebrate UCPs
Gauge Threshold Corrections for Local Orientifolds
We study gauge threshold corrections for systems of fractional branes at
local orientifold singularities and compare with the general Kaplunovsky-Louis
expression for locally supersymmetric N=1 gauge theories. We focus on branes at
orientifolds of the C^3/Z_4, C^3/Z_6 and C^3/Z_6' singularities. We provide a
CFT construction of these theories and compute the threshold corrections. Gauge
coupling running undergoes two phases: one phase running from the bulk winding
scale to the string scale, and a second phase running from the string scale to
the infrared. The first phase is associated to the contribution of N=2 sectors
to the IR beta functions and the second phase to the contribution of both N=1
and N=2 sectors. In contrast, naive application of the Kaplunovsky-Louis
formula gives single running from the bulk winding mode scale. The discrepancy
is resolved through 1-loop non-universality of the holomorphic gauge couplings
at the singularity, induced by a 1-loop redefinition of the twisted blow-up
moduli which couple differently to different gauge nodes. We also study the
physics of anomalous and non-anomalous U(1)s and give a CFT description of how
masses for non-anomalous U(1)s depend on the global properties of cycles.Comment: 44 page
A toy model of fractal glioma development under RF electric field treatment
A toy model for glioma treatment by a radio frequency electric field is
suggested. This low-intensity, intermediate-frequency alternating electric
field is known as the tumor-treating-field (TTF). In the framework of this
model the efficiency of this TTF is estimated, and the interplay between the
TTF and the migration-proliferation dichotomy of cancer cells is considered.
The model is based on a modification of a comb model for cancer cells, where
the migration-proliferation dichotomy becomes naturally apparent. Considering
glioma cancer as a fractal dielectric composite of cancer cells and normal
tissue cells, a new effective mechanism of glioma treatment is suggested in the
form of a giant enhancement of the TTF. This leads to the irreversible
electroporation that may be an effective non-invasive method of treating brain
cancer.Comment: Submitted for publication in European Physical Journal
Model building with intersecting D6-branes on smooth Calabi-Yau manifolds
We study intersecting D6-branes in Calabi-Yau manifolds that are smooth
hypersurfaces in weighted projective spaces. We develop the techniques for
calculating intersection numbers between special Lagrangian sub-manifolds
defined as fixed loci of anti-holomorphic involutions. We present global
Pati-Salam and MSSM-like models that are supersymmetric up to a decoupled
hidden sector.Comment: 29p
D-Terms from Generalized NS-NS Fluxes in Type II
Orientifolds of type II string theory admit a certain set of generalized
NS-NS fluxes, including not only the three-form field strength H, but also
metric and non-geometric fluxes, which are related to H by T-duality. We
describe in general how these fluxes appear as parameters of an effective N=1
supergravity theory in four dimensions, and in particular how certain
generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term
contributions to the effective scalar potential. We illustrate these phenomena
in type IIB with the example of a certain orientifold of T^6/Z_4.Comment: 31+1 pages, uses utarticle.cls; v2: references adde
Non-geometric flux vacua, S-duality and algebraic geometry
The four dimensional gauged supergravities descending from non-geometric
string compactifications involve a wide class of flux objects which are needed
to make the theory invariant under duality transformations at the effective
level. Additionally, complex algebraic conditions involving these fluxes arise
from Bianchi identities and tadpole cancellations in the effective theory. In
this work we study a simple T and S-duality invariant gauged supergravity, that
of a type IIB string compactified on a orientifold with
O3/O7-planes. We build upon the results of recent works and develop a
systematic method for solving all the flux constraints based on the algebra
structure underlying the fluxes. Starting with the T-duality invariant
supergravity, we find that the fluxes needed to restore S-duality can be simply
implemented as linear deformations of the gauge subalgebra by an element of its
second cohomology class. Algebraic geometry techniques are extensively used to
solve these constraints and supersymmetric vacua, centering our attention on
Minkowski solutions, become systematically computable and are also provided to
clarify the methods.Comment: 47 pages, 10 tables, typos corrected, Accepted for Publication in
Journal of High Energy Physic
AdS Vacua, Attractor Mechanism and Generalized Geometries
We consider flux vacua attractor equations in type IIA string theory
compactified on generalized geometries with orientifold projections. The
four-dimensional N=1 superpotential in this compactification can be written as
the sum of the Ramond-Ramond superpotential and a term described by
(non)geometric flux charges. We exhibit a simple model in which supersymmetric
AdS and Minkowski solutions are classified by means of discriminants of the two
superpotentials. We further study various configurations without Ramond-Ramond
flux charges. In this case we find supersymmetric AdS vacua both in the case of
compactifications on generalized geometries with SU(3) x SU(3) structures and
on manifolds with an SU(3)-structure without nongeometric flux charges. In the
latter case, we have to introduce correction terms into the prepotential in
order to realize consistent vacua.Comment: 35 pages, accepted version in JHE
Moduli Redefinitions and Moduli Stabilisation
Field redefinitions occur in string compactifications at the one loop level.
We review arguments for why such redefinitions occur and study their effect on
moduli stabilisation and supersymmetry breaking in the LARGE volume scenario.
For small moduli, although the effect of such redefinitions can be larger than
that of the corrections in both the K\"ahler and scalar potentials,
they do not alter the structure of the scalar potential. For the less well
motivated case of large moduli, the redefinitions can dominate all other terms
in the scalar potential. We also study the effect of redefinitions on the
structure of supersymmetry breaking and soft terms.Comment: 21 pages, 3 figures; v2. references adde
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