1,160 research outputs found
Once more on -vacua in dimensional QED and 3+1 dimensional gluodynamics
Two different but tightly connected problems, and strong CP violation
problems, are discussed in two different models which exhibit both asymptotic
freedom and confinement. One of them is the 3d Polyakov's model of compact QED
and the other is 4d gluodynamics. It is shown that although both these models
possess the long range interactions of the topological charges, only in the
former case physics does not depend on ; while the latter exhibits an
explicit - dependence. The crucial difference is due to the
observation, that the pseudoparticles of 4d gluodynamics possess an aditional
quantum number, apart of the topological charge .Comment: 15 page
Surface finish control by electrochemical polishing in stainless steel 316 pipes
Electrochemical machining (ECM) is a non-conventional machining process which is based on the localised anodic dissolution of any conductive material. One of the main applications of ECM is the polishing of materials with enhanced characteristics, such as high strength, heat-resistance or corrosion-resistance, i.e. electrochemical polishing. The present work presents an evaluation of the parameters involved in the ECM of Stainless Steel 316 (SS316) with the objective of predicting the resulting surface finish on the sample. The interest of studying ECM on SS316 resides on the fact that a repeatable surface finish is not easily achieved. ECM experimental tests on SS316 pipes of 1.5" (0.0381 m) diameter were conducted by varying machining parameters such as voltage, interelectrode gap, electrolyte inlet temperature, and electrolyte flow rate. The surface finish of the samples was then evaluated in order to find the significance of each of these parameters on the surface quality of the end product. Results showed that overvoltage, which is dependent on the interelectrode gap and the electrolyte temperature, is one of the main parameters affecting the surface finish; additionally there is a strong relationship between the resulting surface finish and the electrolyte flow. The interelectrode gap and inlet electrolyte temperature also affect the resulting surface finish but their influence was not so evident in this work. Finally, the variation of the electrolyte temperature during the process was found to have a great impact on the uniformity of the surface finish along the sample. We believe that this contribution enables the tailoring of the surface finish to specific applications while reducing manufacturing costs and duration of the ECM process
Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-
The long-distance contribution via the two-photon intermediate state to the
forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been
studied within the standard model. In order to evaluate the dispersive part of
the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a
phenomenological form factor to soften the ultraviolet behavior of the
transition. It is found that, this long-distance transition, although subject
to some theoretical uncertainties, can lead to significant contributions to the
forward-backward asymmetries, which could be tested in the future high-precise
experiments.Comment: 13 pages, 5 figure
DBI Inflation in the Tip Region of a Warped Throat
Previous work on DBI inflation, which achieves inflation through the motion
of a brane as it moves through a warped throat compactification, has
focused on the region far from the tip of the throat. Since reheating and other
observable effects typically occur near the tip, a more detailed study of this
region is required. To investigate these effects we consider a generalized warp
throat where the warp factor becomes nearly constant near the tip. We find that
it is possible to obtain 60 or more e-folds in the constant region, however
large non-gaussianities are typically produced due to the small sound speed of
fluctuations. For a particular well-studied throat, the Klebanov-Strassler
solution, we find that inflation near the tip may be generic and it is
difficult to satisfy current bounds on non-gaussianity, but other throat
solutions may evade these difficulties.Comment: 26 pages, 1 figure. v1. references added, typos corrected v2.
clarifications mad
Liver-specific insulin receptor isoform A expression enhances hepatic glucose uptake and ameliorates liver steatosis in a mouse model of diet-induced obesity
Among the main complications associated with obesity are insulin
resistance and altered glucose and lipid metabolism within the liver. It
has previously been described that insulin receptor isoform A (IRA)
favors glucose uptake and glycogen storage in hepatocytes compared
with isoform B (IRB), improving glucose homeostasis in mice lacking
liver insulin receptor. Thus, we hypothesized that IRA could also
improve glucose and lipid metabolism in a mouse model of high-fatdiet-induced obesity. We addressed the role of insulin receptor
isoforms in glucose and lipid metabolism in vivo. We expressed IRA
or IRB specifically in the liver by using adeno-associated viruses
(AAVs) in a mouse model of diet-induced insulin resistance and
obesity. IRA, but not IRB, expression induced increased glucose
uptake in the liver and muscle, improving insulin tolerance. Regarding
lipid metabolism, we found that AAV-mediated IRA expression also
ameliorated hepatic steatosis by decreasing the expression of Fasn,
Pgc1a, Acaca and Dgat2 and increasing Scd-1 expression. Taken
together, our results further unravel the role of insulin receptor isoforms
in hepatic glucose and lipid metabolism in an insulin-resistant scenario.
Our data strongly suggest that IRA is more efficient than IRB at favoring
hepatic glucose uptake, improving insulin tolerance and ameliorating
hepatic steatosis. Therefore, we conclude that a gene therapy
approach for hepatic IRA expression could be a safe and promising
tool for the regulation of hepatic glucose consumption and lipid
metabolism, two key processes in the development of non-alcoholic
fatty liver disease associated with obesity
Multiple Inflation, Cosmic String Networks and the String Landscape
Motivated by the string landscape we examine scenarios for which inflation is
a two-step process, with a comparatively short inflationary epoch near the
string scale and a longer period at a much lower energy (like the TeV scale).
We quantify the number of -foldings of inflation which are required to yield
successful inflation within this picture. The constraints are very sensitive to
the equation of state during the epoch between the two inflationary periods, as
the extra-horizon modes can come back inside the horizon and become
reprocessed. We find that the number of -foldings during the first
inflationary epoch can be as small as 12, but only if the inter-inflationary
period is dominated by a network of cosmic strings (such as might be produced
if the initial inflationary period is due to the brane-antibrane mechanism). In
this case a further 20 -foldings of inflation would be required at lower
energies to solve the late universe's flatness and horizon problems.Comment: 27 pages, 6 figures; v2: refences adde
Three-body structure of low-lying 18Ne states
We investigate to what extent 18Ne can be descibed as a three-body system
made of an inert 16O-core and two protons. We compare to experimental data and
occasionally to shell model results. We obtain three-body wave functions with
the hyperspherical adiabatic expansion method. We study the spectrum of 18Ne,
the structure of the different states and the predominant transition strengths.
Two 0+, two 2+, and one 4+ bound states are found where they are all known
experimentally. Also one 3+ close to threshold is found and several negative
parity states, 1-, 3-, 0-, 2-, most of them bound with respect to the 16O
excited 3- state. The structures are extracted as partial wave components, as
spatial sizes of matter and charge, and as probability distributions.
Electromagnetic decay rates are calculated for these states. The dominating
decay mode for the bound states is E2 and occasionally also M1.Comment: 17 pages, 5 figures (version to appear in EPJA
Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength
With SDSS galaxy data and halo data from up-to-date N-body simulations we
construct a semi-empirical catalog (SEC) of early-type systems by making a
self-consistent bivariate statistical match of stellar mass (M_star) and
velocity dispersion (sigma) with halo virial mass (M_vir). We then assign
stellar mass profile and velocity dispersion profile parameters to each system
in the SEC using their observed correlations with M_star and sigma.
Simultaneously, we solve for dark matter density profile of each halo using the
spherical Jeans equation. The resulting dark matter density profiles deviate in
general from the dissipationless profile of NFW or Einasto and their mean inner
density slope and concentration vary systematically with M_vir. Statistical
tests of the distribution of profiles at fixed M_vir rule out the null
hypothesis that it follows the distribution predicted by N-body simulations for
M_vir ~< 10^{13.5-14.5} M_solar. These dark matter profiles imply that dark
matter density is, on average, enhanced significantly in the inner region of
halos with M_vir ~< 10^{13.5-14.5} M_solar supporting halo contraction. The
main characteristics of halo contraction are: (1) the mean dark matter density
within the effective radius has increased by a factor varying systematically up
to ~ 3-4 at M_vir = 10^{12} M_solar, and (2) the inner density slope has a mean
of ~ 1.3 with rho(r) ~ r^{-alpha} and a halo-to-halo rms scatter of
rms(alpha) ~ 0.4-0.5 for 10^{12} M_solar ~< M_vir ~< 10^{13-14} M_solar steeper
than the NFW profile (alpha=1). Based on our results we predict that halos of
nearby elliptical and lenticular galaxies can, in principle, be promising
targets for gamma-ray emission from dark matter annihilation.Comment: 43 pages, 20 figures, JCAP, revised and accepted versio
An Inflationary Model in String Theory
We construct a model of inflation in string theory after carefully taking
into account moduli stabilization. The setting is a warped compactification of
Type IIB string theory in the presence of D3 and anti-D3-branes. The inflaton
is the position of a D3-brane in the internal space. By suitably adjusting
fluxes and the location of symmetrically placed anti-D3-branes, we show that at
a point of enhanced symmetry, the inflaton potential V can have a broad
maximum, satisfying the condition V''/V << 1 in Planck units. On starting close
to the top of this potential the slow-roll conditions can be met. Observational
constraints impose significant restrictions. As a first pass we show that these
can be satisfied and determine the important scales in the compactification to
within an order of magnitude. One robust feature is that the scale of inflation
is low, H = O(10^{10}) GeV. Removing the observational constraints makes it
much easier to construct a slow-roll inflationary model. Generalizations and
consequences including the possibility of eternal inflation are also discussed.
A more careful study, including explicit constructions of the model in string
theory, is left for the future.Comment: 27 pages, LaTeX, 1 eps figure. v2: references adde
de Sitter String Vacua from Supersymmetric D-terms
We propose a new mechanism for obtaining de Sitter vacua in type IIB string
theory compactified on (orientifolded) Calabi-Yau manifolds similar to those
recently studied by Kachru, Kallosh, Linde and Trivedi (KKLT). dS vacuum
appears in KKLT model after uplifting an AdS vacuum by adding an anti-D3-brane,
which explicitly breaks supersymmetry. We accomplish the same goal by adding
fluxes of gauge fields within the D7-branes, which induce a D-term potential in
the effective 4D action. In this way we obtain dS space as a spontaneously
broken vacuum from a purely supersymmetric 4D action. We argue that our
approach can be directly extended to heterotic string vacua, with the dilaton
potential obtained from a combination of gaugino condensation and the D-terms
generated by anomalous U(1) gauge groups.Comment: 17 pages, 1 figur
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