3,905 research outputs found
A general formula of the effective potential in 5D SU(N) gauge theory on orbifold
We show a general formula of the one loop effective potential of the 5D SU(N)
gauge theory compactified on an orbifold, . The formula shows the case
when there are fundamental, (anti-)symmetric tensor and adjoint
representational bulk fields. Our calculation method is also applicable when
there are bulk fields belonging to higher dimensional representations. The
supersymmetric version of the effective potential with Scherk-Schwarz breaking
can be obtained straightforwardly. We also show some examples of effective
potentials in SU(3), SU(5) and SU(6) models with various boundary conditions,
which are reproduced by our general formula.Comment: 22 pages;minor corrections;references added;typos correcte
Gravitating defects of codimension-two
Thin gravitating defects with conical singularities in higher codimensions
and with generalized Israel matching conditions are known to be inconsistent
for generic energy-momentum. A way to remove this inconsistency is proposed and
is realized for an axially symmetric gravitating codimension-two defect in six
dimensional Einstein gravity. By varying with respect to the brane embedding
fields, alternative matching conditions are derived, which are generalizations
of the Nambu-Goto equations of motion of the defect, consistent with bulk
gravity. For a maximally symmetric defect the standard picture is recovered.
The four-dimensional perfect fluid cosmology coincides with conventional FRW in
the case of radiation, but for dust it has rho^{4/3} instead of rho. A
four-dimensional black hole solution is presented having the Schwarzschild form
with a short-distance correction r^{-2}.Comment: Minor changes, to appear in Classical and Quantum Gravit
A Study of Activated Processes in Soft Sphere Glass
On the basis of long simulations of a binary mixture of soft spheres just
below the glass transition, we make an exploratory study of the activated
processes that contribute to the dynamics. We concentrate on statistical
measures of the size of the activated processes.Comment: 17 pages, 9 postscript figures with epsf, uses harvmac.te
One-loop Beta Functions for the Orientable Non-commutative Gross-Neveu Model
We compute at the one-loop order the beta-functions for a renormalisable
non-commutative analog of the Gross Neveu model defined on the Moyal plane. The
calculation is performed within the so called x-space formalism. We find that
this non-commutative field theory exhibits asymptotic freedom for any number of
colors. The beta-function for the non-commutative counterpart of the Thirring
model is found to be non vanishing.Comment: 16 pages, 9 figure
The stability of the O(N) invariant fixed point in three dimensions
We study the stability of the O(N) fixed point in three dimensions under
perturbations of the cubic type. We address this problem in the three cases
by using finite size scaling techniques and high precision Monte
Carlo simulations. It is well know that there is a critical value
below which the O(N) fixed point is stable and above which the cubic fixed
point becomes the stable one. While we cannot exclude that , as recently
claimed by Kleinert and collaborators, our analysis strongly suggests that
coincides with 3.Comment: latex file of 18 pages plus three ps figure
Cognition-Enhancing Drugs: Can We Say No?
Normative analysis of cognition-enhancing drugs frequently weighs the liberty interests of drug users against egalitarian commitments to a level playing field. Yet those who would refuse to engage in neuroenhancement may well find their liberty to do so limited in a society where such drugs are widespread. To the extent that unvarnished emotional responses are world-disclosive, neurocosmetic practices also threaten to provide a form of faulty data to their users. This essay examines underappreciated liberty-based and epistemic rationales for regulating cognition-enhancing drugs
Transmission Resonance in an Infinite Strip of Phason-Defects of a Penrose Approximant Network
An exact method that analytically provides transfer matrices in finite
networks of quasicrystalline approximants of any dimensionality is discussed.
We use these matrices in two ways: a) to exactly determine the band structure
of an infinite approximant network in analytical form; b) to determine, also
analytically, the quantum resistance of a finite strip of a network under
appropriate boundary conditions. As a result of a subtle interplay between
topology and phase interferences, we find that a strip of phason-defects along
a special symmetry direction of a low 2-d Penrose approximant, leads to the
rigorous vanishing of the reflection coefficient for certain energies. A
similar behavior appears in a low 3-d approximant. This type of ``resonance" is
discussed in connection with the gap structure of the corresponding ordered
(undefected) system.Comment: 18 pages special macros jnl.tex,reforder.tex, eqnorder.te
Hidden vector dark matter
We show that dark matter could be made of massive gauge bosons whose
stability doesn't require to impose by hand any discrete or global symmetry.
Stability of gauge bosons can be guaranteed by the custodial symmetry
associated to the gauge symmetry and particle content of the model. The
particle content we consider to this end is based on a hidden sector made of a
vector multiplet associated to a non-abelian gauge group and of a scalar
multiplet charged under this gauge group. The hidden sector interacts with the
Standard Model particles through the Higgs portal quartic scalar interaction in
such a way that the gauge bosons behave as thermal WIMPS. This can lead easily
to the observed dark matter relic density in agreement with the other various
constraints, and can be tested experimentally in a large fraction of the
parameter space. In this model the dark matter direct detection rate and the
annihilation cross section can decouple if the Higgs portal interaction is
weak.Comment: 13 pages, 7 figures, JHEP published version (2009) + update of
section 7 (reference to arXiv:0912.4496
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