26,137 research outputs found
Majorana Fermions Signatures in Macroscopic Quantum Tunneling
Thermodynamic measurements of magnetic fluxes and I-V characteristics in
SQUIDs offer promising paths to the characterization of topological
superconducting phases. We consider the problem of macroscopic quantum
tunneling in an rf-SQUID in a topological superconducting phase. We show that
the topological order shifts the tunneling rates and quantum levels, both in
the parity conserving and fluctuating cases. The latter case is argued to
actually enhance the signatures in the slowly fluctuating limit, which is
expected to take place in the quantum regime of the circuit. In view of recent
advances, we also discuss how our results affect a -junction loop.Comment: 10 pages, 11 figure
NoSOCS in SDSS. VI. The Environmental Dependence of AGN in Clusters and Field in the Local Universe
We investigated the variation in the fraction of optical active galactic
nuclei (AGN) hosts with stellar mass, as well as their local and global
environments. Our sample is composed of cluster members and field galaxies at
and we consider only strong AGN. We find a strong variation in the
AGN fraction () with stellar mass. The field population comprises a
higher AGN fraction compared to the global cluster population, especially for
objects with log . Hence, we restricted our analysis to more
massive objects. We detected a smooth variation in the with local
stellar mass density for cluster objects, reaching a plateau in the field
environment. As a function of clustercentric distance we verify that
is roughly constant for R R, but show a steep decline inwards. We
have also verified the dependence of the AGN population on cluster velocity
dispersion, finding a constant behavior for low mass systems ( km s). However, there is a strong decline in
for higher mass clusters ( 700 km s). When comparing the in
clusters with or without substructure we only find different results for
objects at large radii (R R), in the sense that clusters with
substructure present some excess in the AGN fraction. Finally, we have found
that the phase-space distribution of AGN cluster members is significantly
different than other populations. Due to the environmental dependence of
and their phase-space distribution we interpret AGN to be the result
of galaxy interactions, favored in environments where the relative velocities
are low, typical of the field, low mass groups or cluster outskirts.Comment: 11 pages, 10 figures, Accepted to MNRA
Compact stars with a small electric charge: the limiting radius to mass relation and the maximum mass for incompressible matter
One of the stiffest equations of state for matter in a compact star is
constant energy density and this generates the interior Schwarzschild radius to
mass relation and the Misner maximum mass for relativistic compact stars. If
dark matter populates the interior of stars, and this matter is supersymmetric
or of some other type, some of it possessing a tiny electric charge, there is
the possibility that highly compact stars can trap a small but non-negligible
electric charge. In this case the radius to mass relation for such compact
stars should get modifications. We use an analytical scheme to investigate the
limiting radius to mass relation and the maximum mass of relativistic stars
made of an incompressible fluid with a small electric charge. The investigation
is carried out by using the hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff (TOV) equation, together with the other equations of
structure, with the further hypothesis that the charge distribution is
proportional to the energy density. The approach relies on Volkoff and Misner's
method to solve the TOV equation. For zero charge one gets the interior
Schwarzschild limit, and supposing incompressible boson or fermion matter with
constituents with masses of the order of the neutron mass one gets that the
maximum mass is the Misner mass. For a small electric charge, our analytical
approximating scheme valid in first order in the star's electric charge, shows
that the maximum mass increases relatively to the uncharged case, whereas the
minimum possible radius decreases, an expected effect since the new field is
repulsive aiding the pressure to sustain the star against gravitational
collapse.Comment: 23 pages, no figure
Instanton Corrected Non-Supersymmetric Attractors
We discuss non-supersymmetric attractors with an instanton correction in Type
IIA string theory compactified on a Calabi-Yau three-fold at large volume. For
a stable non-supersymmetric black hole, the attractor point must minimize the
effective black hole potential. We study the supersymmetric as well as
non-supersymmetric attractors for the D0-D4 system with instanton corrections.
We show that in simple models, like the STU model, the flat directions of the
mass matrix can be lifted by a suitable choice of the instanton parameters.Comment: Minor modifications, Corrected typos, 38 pages, 1 figur
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