21,911 research outputs found
Non-radial oscillation modes as a probe of density discontinuities in neutron stars
A phase transition occurring in the inner core of a neutron star could be
associated to a density discontinuity that would affect the frequency spectrum
of the non-radial oscillation modes in two ways. Firstly, it would produce a
softening of the equation of state, leading to more compact equilibrium
configurations and changing the frequency of the fundamental and pressure modes
of the neutron star. Secondly, a new non-zero frequency g-- mode would appear,
associated to each discontinuity. These discontinuity g--modes have typical
frequencies larger than those of g--modes previously studied in the literature
(thermal, core g-- modes, or g--modes due to chemical inhomogeneities in the
outer layers), and smaller than that of the fundamental mode; therefore they
should be distinguishable from the other modes of non radial oscillation. In
this paper we investigate how high density discontinuities change the frequency
spectrum of the non-radial oscillations, in the framework of the general
relativistic theory of stellar perturbations. Our purpose is to understand
whether a gravitational signal, emitted at the frequencies of the quasi normal
modes, may give some clear information on the equation of state of the neutron
star and, in particular, on the parameters that characterize the density
discontinuity. We discuss some astrophysical processes that may be associated
to the excitation of these modes, and estimate how much gravitational energy
should the modes convey to produce a signal detectable by high frequency
gravitational detectors.Comment: submitted to MNRA
String splitting and strong coupling meson decay
We study the decay of high spin mesons using the gauge/string theory
correspondence. The rate of the process is calculated by studying the splitting
of a macroscopic string intersecting a D-brane. The result is applied to the
decay of mesons in N=4 SYM with a small number of flavors and in a gravity dual
of large N QCD. In QCD the decay of high spin mesons is found to be heavily
suppressed in the regime of validity of the supergravity description.Comment: 17 pages, 2 figures. V2: References added. V3: Minor correction
Residue currents associated with weakly holomorphic functions
We construct Coleff-Herrera products and Bochner-Martinelli type residue
currents associated with a tuple of weakly holomorphic functions, and show
that these currents satisfy basic properties from the (strongly) holomorphic
case, as the transformation law, the Poincar\'e-Lelong formula and the
equivalence of the Coleff-Herrera product and the Bochner-Martinelli type
residue current associated with when defines a complete intersection.Comment: 28 pages. Updated with some corrections from the revision process. In
particular, corrected and clarified some things in Section 5 and 6 regarding
products of weakly holomorphic functions and currents, and the definition of
the Bochner-Martinelli type current
Multi Mode Interferometer for Guided Matter Waves
We describe the fundamental features of an interferometer for guided matter
waves based on Y-beam splitters and show that, in a quasi two-dimensional
regime, such a device exhibits high contrast fringes even in a multi mode
regime and fed from a thermal source.Comment: Final version (accepted to PRL
Delocalization power of global unitary operations on quantum information
We investigate how originally localized two pieces of quantum information
represented by a tensor product of two unknown qudit states are delocalized by
performing two-qudit global unitary operations. To characterize the
delocalization power of global unitary operations on quantum information, we
analyze the necessary and sufficient condition to deterministically relocalize
one of the two pieces of quantum information to its original Hilbert space by
using only LOCC. We prove that this LOCC one-piece relocalization is possible
if and only if the global unitary operation is local unitary equivalent to a
controlled-unitary operation. The delocalization power and the entangling power
characterize different non-local properties of global unitary operations.Comment: 14 pages, 1 figur
Spacetime could be simultaneously continuous and discrete in the same way that information can
There are competing schools of thought about the question of whether
spacetime is fundamentally either continuous or discrete. Here, we consider the
possibility that spacetime could be simultaneously continuous and discrete, in
the same mathematical way that information can be simultaneously continuous and
discrete. The equivalence of continuous and discrete information, which is of
key importance in information theory, is established by Shannon sampling
theory: of any bandlimited signal it suffices to record discrete samples to be
able to perfectly reconstruct it everywhere, if the samples are taken at a rate
of at least twice the bandlimit. It is known that physical fields on generic
curved spaces obey a sampling theorem if they possess an ultraviolet cutoff.
Most recently, methods of spectral geometry have been employed to show that
also the very shape of a curved space (i.e., of a Riemannian manifold) can be
discretely sampled and then reconstructed up to the cutoff scale. Here, we
develop these results further, and we here also consider the generalization to
curved spacetimes, i.e., to Lorentzian manifolds
Density functional theory for freezing transition of vortex-line liquid with periodic layer pinning
By the density functional theory for crystallization, it is shown that for
vortex lines in an underlying layered structure a smectic phase with period m=2
can be stabilized by strong layer pinning. The freezing of vortex liquid is
then two-step, a second-order liquid-smectic transition and a first-order
smectic-lattice transition. DFT also indicates that a direct, first-order
liquid-lattice transition preempts the smectic order with m>2 irrespectively of
the pinning strength. Possible H-T phase diagrams are mapped out. Implications
of the DFT results to the interlayer Josephson vortex system in high-Tc
cuprates are given.Comment: 4 pages, 5 figures, references adde
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Beyond viral suppression: the quality of life of people living with HIV in Sweden
Sweden has one of the best HIV treatment outcomes in the world and an estimated 95% of all diagnosed people living with HIV are virally suppressed, but the quality of life (QoL) is understudied. The aim of this study was to examine the associations between variables within sociodemographic, behavioural, clinical, psychological, sexual life, social support and personal resource component and the QoL of people living with HIV in Sweden. Data were derived from a cross-sectional, nation-wide survey completed by 15% (n = 1096) of all people living with HIV and collected at 15 infectious disease clinics and 2 needle exchange sites during 2014. Ordinal univariate and multivariate logistic regression analyses were used to examine associations between potential contributors and QoL. Respondents reported high QoL: 63% rated their QoL 7 or higher on a scale ranging from 0 to 10. QoL was independent of gender, age, mode of HIV transmission and country of origin. Lower QoL was associated with recent homelessness, hazardous alcohol consumption, comorbidities, treatment side-effects, HIV-related physical symptoms, hopelessness, negative self-image, sexual dissatisfaction, and negative changes in sex life after HIV. The QoL of people living with HIV in Sweden was high overall, but still significantly influenced by HIV
Unambiguous comparison of the states of multiple quantum systems
We consider N quantum systems initially prepared in pure states and address
the problem of unambiguously comparing them. One may ask whether or not all
systems are in the same state. Alternatively, one may ask whether or not the
states of all N systems are different. We investigate the possibility of
unambiguously obtaining this kind of information. It is found that some
unambiguous comparison tasks are possible only when certain linear independence
conditions are satisfied. We also obtain measurement strategies for certain
comparison tasks which are optimal under a broad range of circumstances, in
particular when the states are completely unknown. Such strategies, which we
call universal comparison strategies, are found to have intriguing connections
with the problem of quantifying the distinguishability of a set of quantum
states and also with unresolved conjectures in linear algebra. We finally
investigate a potential generalisation of unambiguous state comparison, which
we term unambiguous overlap filtering.Comment: 20 pages, no figure
Cloning and Joint Measurements of Incompatible Components of Spin
A joint measurement of two observables is a {\it simultaneous} measurement of
both quantities upon the {\it same} quantum system. When two quantum-mechanical
observables do not commute, then a joint measurement of these observables
cannot be accomplished by projective measurements alone. In this paper we shall
discuss the use of quantum cloning to perform a joint measurement of two
components of spin associated with a qubit system. We introduce a cloning
scheme which is optimal with respect to this task. This cloning scheme may be
thought to work by cloning two components of spin onto its outputs. We compare
the proposed cloning machine to existing cloners.Comment: 7 pages, 2 figures, submitted to PR
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