650 research outputs found
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
Femtoscopy of the system shape fluctuations in heavy ion collisions
Dipole, triangular, and higher harmonic flow that have an origin in the
initial density fluctuations has gained a lot of attention as they can provide
additional important information about the dynamical properties (e.g.
viscosity) of the system. The fluctuations in the initial geometry should be
also reflected in the detail shape and velocity field of the system at
freeze-out. In this talk I discuss the possibility to measure such fluctuations
by means of identical and non-identical particle interferometry.Comment: 4 pages, Proceedings of Quark Matter 2011 Conference, May 23 - May
28, Annecy, Franc
Magnetic permeability of near-critical 3d abelian Higgs model and duality
The three-dimensional abelian Higgs model has been argued to be dual to a
scalar field theory with a global U(1) symmetry. We show that this duality,
together with the scaling and universality hypotheses, implies a scaling law
for the magnetic permeablity chi_m near the line of second order phase
transition: chi_m ~ t^nu, where t is the deviation from the critical line and
nu ~ 0.67 is a critical exponent of the O(2) universality class. We also show
that exactly on the critical lines, the dependence of magnetic induction on
external magnetic field is quadratic, with a proportionality coefficient
depending only on the gauge coupling. These predictions provide a way for
testing the duality conjecture on the lattice in the Coulomb phase and at the
phase transion.Comment: 11 pages; updated references and small changes, published versio
Neutrino masses in the Lepton Number Violating MSSM
We consider the most general supersymmetric model with minimal particle
content and an additional discrete Z_3 symmetry (instead of R-parity), which
allows lepton number violating terms and results in non-zero Majorana neutrino
masses. We investigate whether the currently measured values for lepton masses
and mixing can be reproduced. We set up a framework in which Lagrangian
parameters can be initialised without recourse to assumptions concerning
trilinear or bilinear superpotential terms, CP-conservation or
intergenerational mixing and analyse in detail the one loop corrections to the
neutrino masses. We present scenarios in which the experimental data are
reproduced and show the effect varying lepton number violating couplings has on
the predicted atmospheric and solar mass^2 differences. We find that with
bilinear lepton number violating couplings in the superpotential of the order 1
MeV the atmospheric mass scale can be reproduced. Certain trilinear
superpotential couplings, usually, of the order of the electron Yukawa coupling
can give rise to either atmospheric or solar mass scales and bilinear
supersymmetry breaking terms of the order 0.1 GeV^2 can set the solar mass
scale. Further details of our calculation, Lagrangian, Feynman rules and
relevant generic loop diagrams, are presented in three Appendices.Comment: 48 pages, 7 figures, v2 references added, typos corrected, published
versio
Dynamical generalization of a solvable family of two-electron model atoms with general interparticle repulsion
Holas, Howard and March [Phys. Lett. A {\bf 310}, 451 (2003)] have obtained
analytic solutions for ground-state properties of a whole family of
two-electron spin-compensated harmonically confined model atoms whose different
members are characterized by a specific interparticle potential energy
u(). Here, we make a start on the dynamic generalization of the
harmonic external potential, the motivation being the serious criticism
levelled recently against the foundations of time-dependent density-functional
theory (e.g. [J. Schirmer and A. Dreuw, Phys. Rev. A {\bf 75}, 022513 (2007)]).
In this context, we derive a simplified expression for the time-dependent
electron density for arbitrary interparticle interaction, which is fully
determined by an one-dimensional non-interacting Hamiltonian. Moreover, a
closed solution for the momentum space density in the Moshinsky model is
obtained.Comment: 5 pages, submitted to J. Phys.
Causality violation and singularities
We show that singularities necessarily occur when a boundary of causality
violating set exists in a space-time under the physically suitable assumptions
except the global causality condition in the Hawking-Penrose singularity
theorems. Instead of the global causality condition, we impose some
restrictions on the causality violating sets to show the occurrence of
singularities.Comment: 11 pages, latex, 2 eps figure
Derivative corrections to the Born-Infeld action through beta-function calculations in N=2 boundary superspace
We calculate the beta-functions for an open string sigma-model in the
presence of a U(1) background. Passing to N=2 boundary superspace, in which the
background is fully characterized by a scalar potential, significantly
facilitates the calculation. Performing the calculation through three loops
yields the equations of motion up to five derivatives on the fieldstrengths,
which upon integration gives the bosonic sector of the effective action for a
single D-brane in trivial bulk background fields through four derivatives and
to all orders in alpha'. Finally, the present calculation shows that demanding
ultra-violet finiteness of the non-linear sigma-model can be reformulated as
the requirement that the background is a deformed stable holomorphic U(1)
bundle.Comment: 25 pages, numerous figure
M5-brane geometries, T-duality and fluxes
We describe a duality relation between configurations of M5-branes in
M-theory and type IIB theory on Taub-NUT geometries with NSNS and RR 3-form
field strength fluxes. The flux parameters are controlled by the angles between
the M5-brane and the (T)duality directions. For one M5-brane, the duality leads
to a family of supersymmetric flux configurations which interpolates between
imaginary self-dual fluxes and fluxes similar to the Polchinski-Strassler kind.
For multiple M5-branes, the IIB configurations are related to fluxes for
twisted sector fields in orbifolds. The dual M5-brane picture also provides a
geometric interpretation for several properties of flux configurations (like
the supersymmetry conditions, their contribution to tadpoles, etc), and for
many non-trivial effects in the IIB side. Among the latter, the dielectric
effect for probe D3-branes is dual to the recombination of probe M5-branes with
background ones; also, a picture of a decay channel for non-supersymmetric
fluxes is suggested.Comment: 30 pages, 3 figure
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