335 research outputs found
Towards uniqueness of degenerate axially symmetric Killing horizon
We examine the linearized equations around extremal Kerr horizon and give
some arguments towards stability of the horizon with respect to generic
(non-symmetric) linear perturbation of near horizon geometry.Comment: 17 page
Positive cosmological constant in loop quantum cosmology
The k=0 Friedmann Lemaitre Robertson Walker model with a positive
cosmological constant and a massless scalar field is analyzed in detail. If one
uses the scalar field as relational time, new features arise already in the
Hamiltonian framework of classical general relativity: In a finite interval of
relational time, the universe expands out to infinite proper time and zero
matter density. In the deparameterized quantum theory, the true Hamiltonian now
fails to be essentially self-adjoint both in the Wheeler DeWitt (WDW) approach
and in LQC. Irrespective of the choice of the self-adjoint extension, the big
bang singularity persists in the WDW theory while it is resolved and replaced
by a big bounce in loop quantum cosmology (LQC). Furthermore, the quantum
evolution is surprisingly insensitive to the choice of the self-adjoint
extension. This may be a special case of an yet to be discovered general
property of a certain class of symmetric operators that fail to be essentially
self-adjoint.Comment: 36 pages, 6 figures, RevTex
Effects of Disorder on Superconductivity of Systems with Coexisting Itinerant Electrons and Local Pairs
We study the influence of diagonal disorder (random site energy) of local
pair (LP) site energies on the superconducting properties of a system of
coexisting local pairs and itinerant electrons described by the (hard-core)
boson-fermion model. Our analysis shows that the properties of such a model
with s-wave pairing can be very strongly affected by the diagonal disorder in
LP subsystem (the randomness of the LP site energies). This is in contrast with
the conventional s-wave BCS superconductors, which according to the Anderson's
theorem are rather insensitive to the diagonal disorder (i.e. to nonmagnetic
impurities). It has been found that the disorder effects depend in a crucial
way on the total particle concentration n and the LP level position DELTA_o and
depending on the parameters the system can exhibit various types of
superconducting behaviour, including the LP-like, intermediate (MIXED)and the
'BCS'-like. In the extended range of {n,DELTA_o} the superconducting ordering
is suppressed by the randomness of the LP site energies and the increasing
disorder induces a changeover from the MIXEDlike behaviour to the BCS-like one,
connected with abrupt reduction of T_c and energy gap to zero. However, there
also exist a definite range of {n,DELTA_o} in which the increasing disorder has
a quite different effect: namely it can substantially enhance T_c or even lead
to the phenomenon which can be called disorder induced superconductivity.
Another interesting effect is a possibility of a disorder induced bound pair
formation of itinerant electrons, connected with the change-over to the LP-like
regime.Comment: 18 pages, 12 figure
Asymmetry and the Neutron Skin in Heavy Nuclei
In heavy nuclei the spatial distribution of protons and neutrons is
different. At CERN SPS energies production of and differs for
, , and scattering. These two facts lead to an impact
parameter dependence of the to ratio in
collisions. A recent experiment at CERN seems to confirm qualitatively these
predictions. It may open a possibility for determination of neutron density
distribution in nuclei.Comment: 6 pages and 2 figures, a talk by A.Szczurek at the international
conference MESON2004, June 4-8, Cracow, Polan
On non-existence of static vacuum black holes with degenerate components of the event horizon
We present a simple proof of the non-existence of degenerate components of
the event horizon in static, vacuum, regular, four-dimensional black hole
spacetimes. We discuss the generalisation to higher dimensions and the
inclusion of a cosmological constant.Comment: latex2e, 9 pages in A
Dark solitons revealed in Lieb-Liniger eigenstates
We study how dark solitons, i.e. solutions of one-dimensional single-particle
nonlinear time-dependent Schr\"odinger equation, emerge from eigenstates of a
linear many-body model of contact interacting bosons moving on a ring, the
Lieb-Liniger model. This long-standing problem was addressed by various groups,
which presented different, seemingly unrelated, procedures to reveal the
solitonic waves directly from the many-body model. Here, we propose a
unification of these results using a simple Ansatz for the many-body eigenstate
of the Lieb-Liniger model, which gives us access to systems of hundreds of
atoms. In this approach, mean-field solitons emerge in a single-particle
density through repeated measurements of particle positions in the Ansatz
state. The post-measurement state turns out to be a wave packet of yrast states
of the reduced system.Comment: 8 pages of the main text + 7 pages of appendice
Cosmic recall and the scattering picture of Loop Quantum Cosmology
The global dynamics of a homogeneous universe in Loop Quantum Cosmology is
viewed as a scattering process of its geometrodynamical equivalent. This
picture is applied to build a flexible (easy to generalize) and not restricted
just to exactly solvable models method of verifying the preservation of the
semiclassicality through the bounce. The devised method is next applied to two
simple examples: (i) the isotropic Friedman Robertson Walker universe, and (ii)
the isotropic sector of the Bianchi I model. For both of them we show, that the
dispersions in the logarithm of the volume ln(v) and scalar field momentum
ln(p_phi) in the distant future and past are related via strong triangle
inequalities. This implies in particular a strict preservation of the
semiclassicality (in considered degrees of freedom) in both the cases (i) and
(ii). Derived inequalities are general: valid for all the physical states
within the considered models.Comment: RevTex4, 19 pages, 3 figure
Entangled-state cryptographic protocol that remains secure even if nonlocal hidden variables exist and can be measured with arbitrary precision
Standard quantum cryptographic protocols are not secure if one assumes that
nonlocal hidden variables exist and can be measured with arbitrary precision.
The security can be restored if one of the communicating parties randomly
switches between two standard protocols.Comment: Shortened version, accepted in Phys. Rev.
Real space inhomogeneities in high temperature superconductors: the perspective of two-component model
The two-component model of high temperature superconductors in its real space
version has been solved using Bogoliubov-de Gennes equations. The disorder in
the electron and boson subsystem has been taken into account. It strongly
modifies the superconducting properties and leads to local variations of the
gap parameter and density of states. The assumption that the impurities mainly
modify boson energies offers natural explanation of the puzzling positive
correlation between the positions of impurities and the values of the order
parameter found in the scanning tunnelling microscopy experiments.Comment: 19 pages, IOPP style include
Rovibrational dynamics of the strontium molecule in the A^1\Sigma_u^+, c^3\Pi_u, and a^3\Sigma_u^+ manifold from state-of-the-art ab initio calculations
State-of-the-art ab initio techniques have been applied to compute the
potential energy curves for the electronic states in the A^1\Sigma_u^+,
c^3\Pi_u, and a^3\Sigma_u^+ manifold of the strontium dimer, the spin-orbit and
nonadiabatic coupling matrix elements between the states in the manifold, and
the electric transition dipole moment from the ground X^1\Sigma_g^+ to the
nonrelativistic and relativistic states in the A+c+a manifold. The potential
energy curves and transition moments were obtained with the linear response
(equation of motion) coupled cluster method limited to single, double, and
linear triple excitations for the potentials and limited to single and double
excitations for the transition moments. The spin-orbit and nonadiabatic
coupling matrix elements were computed with the multireference configuration
interaction method limited to single and double excitations. Our results for
the nonrelativistic and relativistic (spin-orbit coupled) potentials deviate
substantially from recent ab initio calculations. The potential energy curve
for the spectroscopically active (1)0_u^+ state is in quantitative agreement
with the empirical potential fitted to high-resolution Fourier transform
spectra [A. Stein, H. Knoeckel, and E. Tiemann, Eur. Phys. J. D 64, 227
(2011)]. The computed ab initio points were fitted to physically sound
analytical expressions, and used in converged coupled channel calculations of
the rovibrational energy levels in the A+c+a manifold and line strengths for
the A^1\Sigma_u^+ <-- X^1\Sigma_g^+ transitions. Positions and lifetimes of
quasi-bound Feshbach resonances lying above the ^1S + ^3P_1 dissociation limit
were also obtained. Our results reproduce (semi)quantitatively the experimental
data observed thus far. Predictions for on-going and future experiments are
also reported.Comment: Final version, accepted for publication in Journal of Chemical
Physic
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