19,014 research outputs found
Constraining decaying dark matter with neutron stars
The amount of decaying dark matter, accumulated in the central regions in
neutron stars together with the energy deposition rate from decays, may set a
limit on the neutron star survival rate against transitions to more compact
objects provided nuclear matter is not the ultimate stable state of matter and
that dark matter indeed is unstable. More generally, this limit sets
constraints on the dark matter particle decay time, . We find that
in the range of uncertainties intrinsic to such a scenario, masses or and lifetimes s and
s can be excluded in the bosonic or fermionic
decay cases, respectively, in an optimistic estimate, while more
conservatively, it decreases by a factor . We
discuss the validity under which these results may improve with other current
constraints.Comment: 6 pages, 1 figure, matches published versio
Dark Matter Seeding in Neutron Stars
We present a mechanism that may seed compact stellar objects with stable
lumps of quark matter, or {\it strangelets}, through the self-annihilation of
gravitationally accreted WIMPs. We show that dark matter particles with masses
above a few GeV may provide enough energy in the nuclear medium for quark
deconfinement and subsequent strangelet formation. If this happens this effect
may then trigger a partial or full conversion of the star into a strange star.
We set a new limit on the WIMP mass in the few-GeV range that seems to be
consistent with recent indications in dark matter direct detection experiments.Comment: 3 pages, 1 figure. Prepared for 19th Particles and Nuclei
International Conference (PANIC 2011), Boston, USA 25-29 Jul 201
Excited-state quantum phase transitions in a two-fluid Lipkin model
Background: Composed systems have became of great interest in the framework
of the ground state quantum phase transitions (QPTs) and many of their
properties have been studied in detail. However, in these systems the study of
the so called excited-state quantum phase transitions (ESQPTs) have not
received so much attention.
Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is
presented in this work. The study is performed through the Hamiltonian
diagonalization for selected values of the control parameters in order to cover
the most interesting regions of the system phase diagram. [Method:] A
Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting
boson model (IBM) is diagonalized for selected values of the parameters and
properties such as the density of states, the Peres lattices, the
nearest-neighbor spacing distribution, and the participation ratio are
analyzed.
Results: An overview of the spectrum of the two-fluid Lipkin model for
selected positions in the phase diagram has been obtained. The location of the
excited-state quantum phase transition can be easily singled out with the Peres
lattice, with the nearest-neighbor spacing distribution, with Poincar\'e
sections or with the participation ratio.
Conclusions: This study completes the analysis of QPTs for the two-fluid
Lipkin model, extending the previous study to excited states. The ESQPT
signatures in composed systems behave in the same way as in single ones,
although the evidences of their presence can be sometimes blurred. The Peres
lattice turns out to be a convenient tool to look into the position of the
ESQPT and to define the concept of phase in the excited states realm
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