1,133 research outputs found
Non-Linear Sigma Model and asymptotic freedom at the Lifshitz point
We construct the general O(N)-symmetric non-linear sigma model in 2+1
spacetime dimensions at the Lifshitz point with dynamical critical exponent
z=2. For a particular choice of the free parameters, the model is
asymptotically free with the beta function coinciding to the one for the
conventional sigma model in 1+1 dimensions. In this case, the model admits also
a simple description in terms of adjoint currents.Comment: 23 pages, 2 figure
Quantum Geometry and Diffusion
We study the diffusion equation in two-dimensional quantum gravity, and show
that the spectral dimension is two despite the fact that the intrinsic
Hausdorff dimension of the ensemble of two-dimensional geometries is very
different from two. We determine the scaling properties of the quantum gravity
averaged diffusion kernel.Comment: latex2e, 10 pages, 4 figure
Notes on noncommutative supersymmetric gauge theory on the fuzzy supersphere
In these notes we review Klimcik's construction of noncommutative gauge
theory on the fuzzy supersphere. This theory has an exact SUSY gauge symmetry
with a finite number of degrees of freedom and thus in principle it is amenable
to the methods of matrix models and Monte Carlo numerical simulations. We also
write down in this article a novel fuzzy supersymmetric scalar action on the
fuzzy supersphere
Twisted SUSY Invariant Formulation of Chern-Simons Gauge Theory on a Lattice
We propose a twisted SUSY invariant formulation of Chern-Simons theory on a
Euclidean three dimensional lattice. The SUSY algebra to be realized on the
lattice is the N=4 D=3 twisted algebra that was recently proposed by D'Adda et
al.. In order to keep the manifest anti-hermiticity of the action, we introduce
oppositely oriented supercharges. Accordingly, the naive continuum limit of the
action formally corresponds to the Landau gauge fixed version of Chern-Simons
theory with complex gauge group which was originally proposed by Witten. We
also show that the resulting action consists of parity even and odd parts with
different coefficients.Comment: 22 pages, 5 figures; v2,v3 added references, v4 added two paragraphs
and one figure in the summar
Enhanced ULF radiation observed by DEMETER two months around the strong 2010 Haiti earthquake
In this paper we study the energy of ULF electromagnetic waves that have been
recorded by the satellite DEMETER, during its passing over Haiti before and
after a destructive earthquake. This earthquake occurred on 12/1/2010, at
geographic Latitude 18.46o and Longitude 287.47o, with Magnitude 7.0 R.
Specifically, we are focusing on the variations of energy of Ez-electric field
component concerning a time period of 100 days before and 50 days after the
strong earthquake. In order to study these variations, we developed a novel
method that can be divided in two stages: first we filter the signal keeping
only the very low frequencies and afterwards we eliminate its trend using
techniques of Singular Spectrum Analysis, combined with a third-degree
polynomial filter. As it is shown, a significant increase in energy is observed
for the time interval of 30 days before the strong earthquake. This result
clearly indicates that the change in the energy of ULF electromagnetic waves
could be related to strong precursory earthquake phenomena. Moreover, changes
in energy were also observed 25 days after the strong earthquake associated
with strong aftershock activity. Finally, we present results concerning the
comparison in changes in Energy during night and day passes of the satellite
over Haiti, which showed differences in the mean energy values, but similar
results as far as the rate of energy change is concerned.Comment: 16 pages, 7 figures, submitted to NHES
Gauged Fermionic Q-balls
We present a new model for a non-topological soliton (NTS) that contains
interacting fermions, scalar particles and a gauge field. Using a variational
approach, we estimate the energy of the localized configuration, showing that
it can be the lowest energy state of the system for a wide range of parameters.Comment: 5 pages, 2 figures; revised version to appear in Phys. Rev.
A new perspective on matter coupling in 2d quantum gravity
We provide compelling evidence that a previously introduced model of
non-perturbative 2d Lorentzian quantum gravity exhibits (two-dimensional)
flat-space behaviour when coupled to Ising spins. The evidence comes from both
a high-temperature expansion and from Monte Carlo simulations of the combined
gravity-matter system. This weak-coupling behaviour lends further support to
the conclusion that the Lorentzian model is a genuine alternative to Liouville
quantum gravity in two dimensions, with a different, and much `smoother'
critical behaviour.Comment: 24 pages, 7 figures (postscript
Facility Location in Evolving Metrics
Understanding the dynamics of evolving social or infrastructure networks is a
challenge in applied areas such as epidemiology, viral marketing, or urban
planning. During the past decade, data has been collected on such networks but
has yet to be fully analyzed. We propose to use information on the dynamics of
the data to find stable partitions of the network into groups. For that
purpose, we introduce a time-dependent, dynamic version of the facility
location problem, that includes a switching cost when a client's assignment
changes from one facility to another. This might provide a better
representation of an evolving network, emphasizing the abrupt change of
relationships between subjects rather than the continuous evolution of the
underlying network. We show that in realistic examples this model yields indeed
better fitting solutions than optimizing every snapshot independently. We
present an -approximation algorithm and a matching hardness result,
where is the number of clients and the number of time steps. We also
give an other algorithms with approximation ratio for the variant
where one pays at each time step (leasing) for each open facility
Non-Commutativity of the Zero Chemical Potential Limit and the Thermodynamic Limit in Finite Density Systems
Monte Carlo simulations of finite density systems are often plagued by the
complex action problem. We point out that there exists certain
non-commutativity in the zero chemical potential limit and the thermodynamic
limit when one tries to study such systems by reweighting techniques. This is
demonstrated by explicit calculations in a Random Matrix Theory, which is
thought to be a simple qualitative model for finite density QCD. The
factorization method allows us to understand how the non-commutativity, which
appears at the intermediate steps, cancels in the end results for physical
observables.Comment: 7 pages, 9 figure
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