8,619 research outputs found
Towards a Novel no-hair Theorem for Black Holes
We provide strong numerical evidence for a new no-scalar-hair theorem for
black holes in general relativity, which rules out spherical scalar hair of
static four dimensional black holes if the scalar field theory, when coupled to
gravity, satisfies the Positive Energy Theorem. This sheds light on the
no-scalar-hair conjecture for Calabi-Yau compactifications of string theory,
where the effective potential typically has negative regions but where
supersymmetry ensures the total energy is always positive. In theories where
the scalar tends to a negative local maximum of the potential at infinity, we
find the no-scalar-hair theorem holds provided the asymptotic conditions are
invariant under the full anti-de Sitter symmetry group.Comment: 25 pages, 11 figure
Relativistic particle dynamics in D=2+1
We propose a SUSY variant of the action for a massless spinning particles via
the inclusion of twistor variables. The action is constructed to be invariant
under SUSY transformations and -reparametrizations even when an
interaction field is including. The constraint analysis is achieved and the
equations of motion are derived. The commutation relations obtained for the
commuting spinor variables show that the particle states have
fractional statistics and spin. At once we introduce a possible massive term
for the non-interacting model.Comment: 11 page
Order of the Chiral and Continuum Limits in Staggered Chiral Perturbation Theory
Durr and Hoelbling recently observed that the continuum and chiral limits do
not commute in the two dimensional, one flavor, Schwinger model with staggered
fermions. I point out that such lack of commutativity can also be seen in
four-dimensional staggered chiral perturbation theory (SChPT) in quenched or
partially quenched quantities constructed to be particularly sensitive to the
chiral limit. Although the physics involved in the SChPT examples is quite
different from that in the Schwinger model, neither singularity seems to be
connected to the trick of taking the nth root of the fermion determinant to
remove unwanted degrees of freedom ("tastes"). Further, I argue that the
singularities in SChPT are absent in most commonly-computed quantities in the
unquenched (full) QCD case and do not imply any unexpected systematic errors in
recent MILC calculations with staggered fermions.Comment: 14 pages, 1 figure. v3: Spurious symbol, introduced by conflicting
tex macros, removed. Clarification of discussion in several place
rho(omega)-> pi^0 pi^0 gamma, rho(omega) -> eta pi^0 gamma decays in the local quark Nambu--Jona-Lasinio model
The branching ratios and photon spectra of the rare processes rho(omega)->
pi^0 pi^0 gamma, rho(omega) -> eta pi^0 gamma are calculated in the framework
of the standard local quark Nambu--Jona-Lasinio (NJL) model. Three types of
diagrams are considered: the quark box and the pole diagrams with scalar
(sigma,a_0(980)) and vector (rho,omega) mesons. The obtained estimations for
the widths of the processes rho(omega)-> pi^0 pi^0 gamma are in satisfactory
agreement with existing experimental data. Predictions are made for the widths
of the processes rho(omega) -> eta pi^0 gamma.Comment: 6 pages, 5 figure
Finitely generated ideal languages and synchronizing automata
We study representations of ideal languages by means of strongly connected
synchronizing automata. For every finitely generated ideal language L we
construct such an automaton with at most 2^n states, where n is the maximal
length of words in L. Our constructions are based on the De Bruijn graph.Comment: Submitted to WORDS 201
Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
Fermi gas with time-dependent pairing interaction hosts several different
dynamical states. Coupling between the collective BCS pairing mode and
individual Cooper pair states can make the latter either synchronize or
dephase. We describe transition from phase-locked undamped oscillations to
Landau-damped dephased oscillations in the collisionless, dissipationless
regime as a function of coupling strength. In the dephased regime, we find a
second transition at which the long-time asymptotic pairing amplitude vanishes.
Using a combination of numerical and analytical methods we establish a
continuous (type II) character of both transitions
Contributions of semi-hadronic states to amm of muon, in frames of Nambu-Jona-Lasinio model
We calculate the contribution of semi-hadronic states with pseudoscalar
and scalar ((550))meson accompanied with real photon as
an intermediate state of a heavy photon to the anomalous magnetic moment of
muon. We consider the intermediate states with and as a
hadrons in frames of Nambu-Jona-Lasinio model. The contribution of
state is in agreement with results obtained in previous
theoretical considerations as well as with experimental data
, besides we estimate
We
discass as well the LbL mechanism with Comment: 6 pages, 2 figure
Anomalous transport in normal-superconducting and ferromagnetic-superconducting nanostructures
We have calculated the temperature dependence of the conductance variation
() of mesoscopic superconductor normal metal(S/N) structures, in
the diffusive regime, analysing both weak and strong proximity effects. We show
that in the case of a weak proximity effect there are two peaks in the
dependence of on temperature. One of them (known from previous
studies) corresponds to a temperature of order of the Thouless energy
(), and another, newly predicted maximum, occurs at a
temperature where the energy gap in the superconductor is
of order . In the limit the temperature is
determined by ( is the phase breaking length),
and not . We have also calculated the voltage dependence for a S/F structure (F is a ferromagnet) and predict non-monotonic
behaviour at voltages of order the Zeeman splitting.Comment: 6 figures. Submitted to PRB Rapid com
Suppression and enhancement of the critical current in multiterminal S/N/S mesoscopic structures
We analyse the measured critical current in a mesoscopic
4-terminal S/N/S structure. The current through the S/N interface is shown to
consist not only of the Josephson component but also a
phase-coherent part of the subgap current. The current
is determined by the both components and and depends
in a nonmonotonic way on the voltage between superconductors and normal
reservoirs reaching a maximum at . The obtained theoretical
resultas are in qualitative agreement with recent experimental data.Comment: 4 page, 3 figures. To be puplished in PRB Rapid co
Slowly Rotating Non-Abelian Black Holes
It is shown that the well-known non-Abelian static SU(2) black hole solutions
have rotating generalizations, provided that the hypothesis of linearization
stability is accepted. Surprisingly, this rotating branch has an asymptotically
Abelian gauge field with an electric charge that cannot vanish, although the
non-rotating limit is uncharged. We argue that this may be related to our
second finding, namely that there are no globally regular slowly rotating
excitations of the particle-like Bartnik-McKinnon solutions.Comment: 8 pages, LaTe
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