104 research outputs found
Renormalized Kaluza-Klein theories
Using six-dimensional quantum electrodynamics () as an example we
study the one-loop renormalization of the theory both from the six and
four-dimensional points of view. Our main conclusion is that the properly
renormalized four dimensional theory never forgets its higher dimensional
origin. In particular, the coefficients of the neccessary extra counterterms in
the four dimensional theory are determined in a precise way. We check our
results by studying the reduction of on a two-torus.Comment: LaTeX, 36 pages. A new section added; references improved, typos
fixe
Effective potential and stability of the rigid membrane
The calculation of the effective potential for fixed-end and toroidal rigid
-branes is performed in the one-loop as well as in the approximations.
The analysis of the involved zeta-functions (of inhomogeneous Epstein type)
which appear in the process of regularization is done in full detail.
Assymptotic formulas (allowing only for exponentially decreasing errors of
order ) are found which carry all the dependences on the basic
parameters of the theory explicitly. The behaviour of the effective potential
(specified to the membrane case ) is investigated, and the extrema of this
effective potential are obtained.Comment: 15 PAGE
Supergravity interacting with bosonic p-branes and local supersymmetry
We study the coupling of supergravity with a purely bosonic brane source
(bosonic p-brane). The interaction, described by the sum of their respective
actions, is self-consistent if the bosonic p-brane is the pure bosonic limit of
a super-p-brane. In that case the dynamical system preserves 1/2 of the local
supersymmetry characteristic of the `free' supergravity.Comment: 11 pages, RevTe
Partition Functions for the Rigid String and Membrane at Any Temperature
Exact expressions for the partition functions of the rigid string and
membrane at any temperature are obtained in terms of hypergeometric functions.
By using zeta function regularization methods, the results are analytically
continued and written as asymptotic sums of Riemann-Hurwitz zeta functions,
which provide very good numerical approximations with just a few first terms.
This allows to obtain systematic corrections to the results of Polchinski et
al., corresponding to the limits and of
the rigid string, and to analyze the intermediate range of temperatures. In
particular, a way to obtain the Hagedorn temperature for the rigid membrane is
thus found.Comment: 20 pages, LaTeX file, UB-ECM-PF 93/
Verbal working memory and functional large-scale networks in schizophrenia
The aim of this study was to test whether bilinear and nonlinear effective connectivity (EC) measures of working memory fMRI data can differentiate between patients with schizophrenia (SZ) and healthy controls (HC). We applied bilinear and nonlinear Dynamic Causal Modeling (DCM) for the analysis of verbal working memory in 16 SZ and 21 HC. The connection strengths with nonlinear modulation between the dorsolateral prefrontal cortex (DLPFC) and the ventral tegmental area/substantia nigra (VTA/SN) were evaluated. We used Bayesian Model Selection at the group and family levels to compare the optimal bilinear and nonlinear models. Bayesian Model Averaging was used to assess the connection strengths with nonlinear modulation. The DCM analyses revealed that SZ and HC used different bilinear networks despite comparable behavioral performance. In addition, the connection strengths with nonlinear modulation between the DLPFC and the VTA/SN area showed differences between SZ and HC. The adoption of different functional networks in SZ and HC indicated neurobiological alterations underlying working memory performance, including different connection strengths with nonlinear modulation between the DLPFC and the VTA/SN area. These novel findings may increase our understanding of connectivity in working memory in schizophrenia
First-order quasilinear canonical representation of the characteristic formulation of the Einstein equations
We prescribe a choice of 18 variables in all that casts the equations of the
fully nonlinear characteristic formulation of general relativity in
first--order quasi-linear canonical form. At the analytical level, a
formulation of this type allows us to make concrete statements about existence
of solutions. In addition, it offers concrete advantages for numerical
applications as it now becomes possible to incorporate advanced numerical
techniques for first order systems, which had thus far not been applicable to
the characteristic problem of the Einstein equations, as well as in providing a
framework for a unified treatment of the vacuum and matter problems. This is of
relevance to the accurate simulation of gravitational waves emitted in
astrophysical scenarios such as stellar core collapse.Comment: revtex4, 7 pages, text and references added, typos corrected, to
appear in Phys. Rev.
Effective action and brane running
We address the renormalized effective action for a Randall-Sundrum brane
running in 5d bulk space. The running behavior of the brane action is obtained
by shifting the brane-position without changing the background and the
fluctuations. After an appropriate renormalization, we obtain an effective, low
energy braneworld action, in which the effective 4d Planck mass is independent
of the running-position. We address some implications of this effective action.Comment: 15 pages, no figur
On the stability of the anomaly-induced inflation
We analyze various phases of inflation based on the anomaly-induced effective
action of gravity (modified Starobinsky model), taking the cosmological
constant Lambda and k=0, +/- 1 topologies into account. The total number of the
inflationary e-folds may be enormous, but at the last 65 of them the inflation
greatly slows down due to the contributions of the massive particles. For the
supersymmetric particle content, the stability of inflation holds from the
initial point at the sub-Planck scale until the supersymmetry breaks down.
After that the universe enters into the unstable regime with the eventual
transition into the stable FRW-like evolution with small positive cosmological
constant. It is remarkable, that all this follows automatically, without
fine-tuning of any sort, independent on the values of Lambda and k. Finally, we
consider the stability under the metric perturbations during the last 65
e-folds of inflation and find that the amplitude of the ones with the
wavenumber below a certain cutoff has an acceptable range.Comment: 27 pages, LaTeX, 8 figures, some misprints correcte
Gauge-gravity correspondence in de Sitter braneworld
We study the braneworld solutions based on a solvable model of 5d gauged
supergravity with two scalars of conformal dimension three, which correspond to
bilinear operators of fermions in the dual super Yang-Mills
theory on the boundary. An accelerating braneworld solution is obtained when
both scalars are taken as the form of deformations of the super Yang-Mills
theory and the bulk supersymmetry is broken. This solution is smoothly
connected to the Poincare invariant brane in the limit of vanishing
cosmological constant. The stability of this brane-solution and the
correspondence to the gauge theory are addressed.Comment: 16 pages, 1 figur
Non-Abelian Brane Worlds: The Heterotic String Story
We discuss chiral supersymmetric compactifications of the SO(32) heterotic
string on Calabi-Yau manifolds equipped with direct sums of stable bundles with
structure group U(n). In addition we allow for non-perturbative heterotic
five-branes. These models are S-dual to Type I compactifications with D9- and
D5-branes, which by themselves are mirror symmetric to general intersecting
D6-brane models. For the construction of concrete examples we consider
elliptically fibered Calabi-Yau manifolds with SU(n) bundles given by the
spectral cover construction. The U(n) bundles are obtained via twisting by line
bundles. We present a four-generation Pati-Salam and a three-generation
Standard-like model.Comment: 29 pages, 7 tables, LATEX; v2: refs adde
- âŠ