796 research outputs found

### Nonequilibrium work distribution of a quantum harmonic oscillator

We analytically calculate the work distribution of a quantum harmonic
oscillator with arbitrary time-dependent angular frequency. We provide detailed
expressions for the work probability density for adiabatic and nonadiabatic
processes, in the limit of low and high temperature. We further verify the
validity of the quantum Jarzynski equalityComment: 6 pages, 3 figure

### Comments on dihedral and supersymmetric extensions of a family of Hamiltonians on a plane

For any odd $k$, a connection is established between the dihedral and
supersymmetric extensions of the Tremblay-Turbiner-Winternitz Hamiltonians
$H_k$ on a plane. For this purpose, the elements of the dihedral group $D_{2k}$
are realized in terms of two independent pairs of fermionic creation and
annihilation operators and some interesting trigonometric identities are
demonstrated.Comment: 10 pages, no figure, acknowledgments added, references completed,
published versio

### Defining integrals over connections in the discretized gravitational functional integral

Integration over connection type variables in the path integral for the
discrete form of the first order formulation of general relativity theory is
studied. The result (a generalized function of the rest of variables of the
type of tetrad or elementary areas) can be defined through its moments, i. e.
integrals of it with the area tensor monomials. In our previous paper these
moments have been defined by deforming integration contours in the complex
plane as if we had passed to an Euclidean-like region. In the present paper we
define and evaluate the moments in the genuine Minkowsky region. The
distribution of interest resulting from these moments in this non-positively
defined region contains the divergences. We prove that the latter contribute
only to the singular (\dfun like) part of this distribution with support in the
non-physical region of the complex plane of area tensors while in the physical
region this distribution (usual function) confirms that defined in our previous
paper which decays exponentially at large areas. Besides that, we evaluate the
basic integrals over which the integral over connections in the general path
integral can be expanded.Comment: 18 page

### Non-relativistic limit of multidimensional gravity: exact solutions and applications

It is found the exact solution of the Poisson equation for the
multidimensional space with topology $M_{3+d}=\mathbb{R}^3\times T^d$. This
solution describes smooth transition from the newtonian behavior $1/r_3$ for
distances bigger than periods of tori (the extra dimension sizes) to
multidimensional behavior $1/r^{1+d}_{3+d}$ in opposite limit. In the case of
one extra dimension $d=1$, the gravitational potential is expressed via compact
and elegant formula. These exact solutions are applied to some practical
problems to get the gravitational potentials for considered configurations.
Found potentials are used to calculate the acceleration for point masses and
gravitational self-energy.It is proposed models where the test masses are
smeared over some (or all) extra dimensions. In 10-dimensional spacetime with 3
smeared extra dimensions, it is shown that the size of 3 rest extra dimensions
can be enlarged up to submillimeter for the case of 1TeV fundamental Planck
scale $M_{Pl(10)}$. In the models where all extra dimensions are smeared, the
gravitational potential exactly coincides with the newtonian one regardless of
size of the extra dimensions. Nevertheless, the hierarchy problem can be solved
in these models.Comment: LaTex file, 18 pages, 4 figure

### Vacuum polarization in a cosmic string spacetime induced by flat boundary

In this paper we analyze the vacuum expectation values of the field squared
and the energy-momentum tensor associated to a massive scalar field in a higher
dimensional cosmic string spacetime, obeying Dirichlet or Neumann boundary
conditions on the surface orthogonal to the string.Comment: 12 pages, 5 figures, talk presented at the 8th Alexander Friedmann
International Seminar on Gravitation and Cosmology, in Rio de Janeiro, Brazi

### Spectral signatures of magnetic Bloch oscillations in one-dimensional easy-axis ferromagnets

Domain walls in a one-dimensional gapped easy-axis ferromagnet can exhibit
Bloch oscillations in an applied magnetic field. We investigate how exchange
couplings modify this behavior within an approximation based on noninteracting
domain-wall bound states. In particular, we obtain analytical results for the
spectrum and the dynamic structure factor, and show where in momentum space to
expect equidistant energy levels, the Wannier-Zeeman ladder, which is the
spectral signature of magnetic Bloch oscillations. We compare our results to
previous calculations employing a single domain-wall approximation, and make
predictions relevant for the material $CoCl2\cdot2H2O$.Comment: 12 pages, 14 figure

### Relaxational dynamics in 3D randomly diluted Ising models

We study the purely relaxational dynamics (model A) at criticality in
three-dimensional disordered Ising systems whose static critical behaviour
belongs to the randomly diluted Ising universality class. We consider the
site-diluted and bond-diluted Ising models, and the +- J Ising model along the
paramagnetic-ferromagnetic transition line. We perform Monte Carlo simulations
at the critical point using the Metropolis algorithm and study the dynamic
behaviour in equilibrium at various values of the disorder parameter. The
results provide a robust evidence of the existence of a unique model-A dynamic
universality class which describes the relaxational critical dynamics in all
considered models. In particular, the analysis of the size-dependence of
suitably defined autocorrelation times at the critical point provides the
estimate z=2.35(2) for the universal dynamic critical exponent. We also study
the off-equilibrium relaxational dynamics following a quench from T=\infty to
T=T_c. In agreement with the field-theory scenario, the analysis of the
off-equilibrium dynamic critical behavior gives an estimate of z that is
perfectly consistent with the equilibrium estimate z=2.35(2).Comment: 38 page

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