72 research outputs found
Remarks on cosmological issues in some string theoretic brane worlds
We examine, in the context of certain string compactifications resulting in
five dimensional brane worlds the mechanisms of (self) tuning of the
cosmological constant and the recovery of standard cosmological evolution. We
show that self tuning can occur only as long as supersymmetry is unbroken
(unless additional assumptions are made) and that the adjustment of the
cosmological constant to zero after supersymmetry breaking and the recovery of
standard evolution are the same problem verifying previously made statements in
the context of general i.e. not necessarily string theoretic brane worlds. We
emphasize, however, that contrary to general brane worlds where the above
adjustment requires a fine tuning, stringy brane worlds contain an additional
integration constant due to the presence of the compact space thus allowing the
adjustment to be done only with integration constants.Comment: Talk given at the "M-theory Cosmology" conference in Cambridge,
England and at various other place
Flavor Corrections in the Static Potential in Holographic QCD
We examine the static potential in the presence of flavors in the
perturbative backreacted D4/D8 system from localized D8 branes, focusing in
particular on the Sakai-Sugimoto model. For the case of long strings we find
the flavor corrections to the static potential which are of exponential form.
We then investigate shorter Wilson loops and express their energy analytically
in terms of the lengths of two neighboring Wilson loops. Moreover, we find that
the static force for all the cases in the backreacted background is reduced
compared to one in the probe limit, as expected due to screening effects. We
also compare the string world-sheets in the two backgrounds and find how they
get modified by the backreaction. Our results are supported by numerical
computations as well. Finally we discuss our results in comparison with the
lattice data and comment on the issue of physical scales which seem to lie at
the heart of the reason that obstructs our model at this level to fully
describe QCD.Comment: 28 pages, 3 figure
Non-perturbative Gauge-Higgs Unification: Symmetries and Order Parameters
We consider pure SU(N) gauge theories defined on an orbifold lattice,
analogous to the S^1/Z_2 gauge theory orbifolds of the continuum, which
according to the perturbative analysis do not have a Higgs phase.
Non-perturbatively the conclusion for N even is the opposite, namely that
spontaneous symmetry breaking does take place and some of the gauge bosons
become massive. We interpret this new, non-perturbative phenomenon both
mathematically and physically.Comment: 25 pages, 1 figure; figure added and text improve
A new model for confinement
We propose a new approach towards the understanding of confinement. Starting
from an anisotropic five dimensional pure gauge theory, we approach a second
order phase transition where the system reduces dimensionally. Dimensional
reduction is realized via localization of the gauge and scalar degrees of
freedom on four dimensional branes. The gauge coupling deriving from the brane
Wilson loop observable runs like an asymptotically free coupling at short
distance, while it exhibits clear signs of string formation at long distance.
The regularization used is the lattice. We take the continuum limit by keeping
the ratio of the lattice spacing in the brane over the lattice spacing along
the extra dimension constant and smaller than one.Comment: 16 pages, 4 figures; references adde
On the holographic width of flux tubes
We investigate the width of the flux tube between heavy static quark charges.
Using the gauge/gravity duality, we find the properties of the minimal
connected surface related to the width of the bound state. We show that in the
confining phase, the logarithmic broadening predicted by the effective string
description and observed in lattice simulations is a generic property of all
confining backgrounds. We also study the transverse fluctuations of the string
connecting two static quarks in curved backgrounds. Our formalism is applied to
AdS space where we compute the expectation value of the square of transverse
deviations of the string, a quantity related to the width.Comment: 1+28 pages, 6 figure
On the construction of Chern-Simons terms in the presence of flux
We develop a method for relating the boundary effective action associated
with an orbifold of the D+1 dimensional theory of a p-form field to D
dimensional fluxed Chern-Simons type of terms. We apply the construction to
derive from twelve dimensions the Chern-Simons terms of the eleven dimensional
supergravity theory in the presence of flux.Comment: Minor corrections mad
Folding Froggatt-Nielsen into the Stueckelberg-Higgs mechanism in anomalous U(1) models
We describe a simple connection between the Froggatt-Nielsen, Stueckelberg
and Higgs mechanisms, all three of them combined in a consistent way. This is
illustrated in the context of a class of generalizations of the Standard Model
with a gauge structure extended by a certain number of anomalous U(1) factors.
These are built in the effective action in a way that gauge invariance and
unitarity are preserved.
Among other features, a physical axion with properties different from those
of a Peccei-Quinn axion emerges.Comment: 9 pages, Based on talks presented at HEP2006, Recent Developments in
High Energy Physics and Cosmology, The Annual Workshop of the Hellenic
Society for the study of High Energy Physics, Ioannina, Greece, April 13-16,
2006. Some extra material include
Renormalization of the Abelian-Higgs Model in the R-xi and Unitary gauges and the physicality of its scalar potential
We perform an old school, one-loop renormalization of the Abelian-Higgs model
in the Unitary and gauges, focused on the scalar potential and the
gauge boson mass. Our goal is to demonstrate in this simple context the
validity of the Unitary gauge at the quantum level, which could open the way
for an until now (mostly) avoided framework for loop computations. We indeed
find that the Unitary gauge is consistent and equivalent to the gauge
at the level of -functions. Then we compare the renormalized, finite,
one-loop Higgs potential in the two gauges and we again find equivalence. This
equivalence needs not only a complete cancellation of the gauge fixing
parameter from the gauge potential but also requires its
-independent part to be equal to the Unitary gauge result. We follow the
quantum behaviour of the system by plotting Renormalization Group trajectories
and Lines of Constant Physics, with the former the well known curves and with
the latter, determined by the finite parts of the counter-terms, particularly
well suited for a comparison with non-perturbative studies.Comment: 111 pages, 16 figures. In the previous version a factor of 2,
regarding the irreducible triangle diagram with only Higgs fields inside the
loop, was missed. In this version the missing factor is corrected and due to
that, some of the plots have been updated. Minor typos correcte
- …