439 research outputs found
Neutrino Emission from Goldstone Modes in Dense Quark Matter
We calculate neutrino emissivities from the decay and scattering of Goldstone
bosons in the color-flavor-locked (CFL) phase of quarks at high baryon density.
Interactions in the CFL phase are described by an effective low-energy theory.
For temperatures in the tens of keV range, relevant to the long-term cooling of
neutron stars, the emissivities involving Goldstone bosons dominate over those
involving quarks, because gaps in the CFL phase are MeV while the
masses of Goldstone modes are on the order of 10 MeV. For the same reason, the
specific heat of the CFL phase is also dominated by the Goldstone modes.
Notwithstanding this, both the emissivity and the specific heat from the
massive modes remain rather small, because of their extremely small number
densities. The values of the emissivity and the specific heat imply that the
timescale for the cooling of the CFL core in isolation is y,
which makes the CFL phase invisible as the exterior layers of normal matter
surrounding the core will continue to cool through significantly more rapid
processes. If the CFL phase appears during the evolution of a proto-neutron
star, neutrino interactions with Goldstone bosons are expected to be
significantly more important since temperatures are high enough (
MeV) to admit large number densities of Goldstone modes.Comment: 29 pages, no figures. slightly modified text, one new eqn. and new
refs. adde
Private information via the Unruh effect
In a relativistic theory of quantum information, the possible presence of
horizons is a complicating feature placing restrictions on the transmission and
retrieval of information. We consider two inertial participants communicating
via a noiseless qubit channel in the presence of a uniformly accelerated
eavesdropper. Owing to the Unruh effect, the eavesdropper's view of any encoded
information is noisy, a feature the two inertial participants can exploit to
achieve perfectly secure quantum communication. We show that the associated
private quantum capacity is equal to the entanglement-assisted quantum capacity
for the channel to the eavesdropper's environment, which we evaluate for all
accelerations.Comment: 5 pages. v2: footnote deleted and typos corrected. v3: major
revision. New capacity (single-letter!) theorem and implicit assumption
lifte
Gas-liquid transition in the model of particles interacting at high energy
An application of the ideas of the inertial confinement fusion process in the
case of particles interacting at high energy is investigated. A possibility of
the gas-liquid transition in the gas is considered using different approaches.
In particular, a shock wave description of interactions between particles is
studied and a self-similar solution of Euler's equation is discussed.
Additionally, Boltzmann equation is solved for self-consistent field (Vlasov's
equation) in linear approximation for the case of a gas under external pressure
and the corresponding change of Knudsen number of the system is calculated.Comment: 24 pages, 2 figur
Development of electric resistance sintering process for the fabrication of hard metals: Processing, microstructure and mechanical properties
This work presents the development of the Electrical Resistance Sintering (ERS) process for the fabrication of hard metals. The compositions of the materials produced were WC with 6 and 10 wt% of Co. In addition to the specific characteristics of the technology, the characterization of the produced parts is presented and compared to materials obtained by conventional processes.
The parts produced by ERS present densities comparable to the ones obtained by conventional methods. The microstructural comparison shows a considerable grain size reduction in the ERS materials which consequently brings a hardness increase. ERS materials show similar fracture toughness to conventional ones.
The very fast sintering allows performing the process without any protective atmosphere, therefore making this process very attractive for the production of materials that need to be sintered under non-oxidising environments. The total duration of the cycle, including heating, holding time and cooling is few seconds.
Finally, some considerations about the scale up and possible industrialization of the technology are explained.This work is financially supported by the Seventh Framework Program
of the Commission of the European Communities under project
EFFIPRO contract no. NMP2-SL-2013-608729
Finite Temperature Correlators in the Schwinger Model
We discuss the correlation function of hadronic currents in the Schwinger
model at finite temperature . We explicitly construct the retarded
correlator in real time and obtain analytical results for the Euclidean
correlator on a torus. Both constructions lead to the same finite temperature
spectral function. The spatial screening lengths in the mesonic channels are
related to the dynamical meson mass and not even in
the infinite temperature limit. The relevance of our results for the finite
temperature problem in four dimensions is discussed.Comment: in LATEX, 30 pages; two figures available on request from the
authors; USITP-93-19, SUNY-NTG-43, (explanations to the figures have been
clarified
Formation of an ordered phase in neutron star matter
In this work, we explore the possible formation of ordered phases in hadronic
matter, related to the presence of hyperons at high densities. We analyze a
microscopic mechanism which can lead to the crystallization of the hyperonic
sector by the confinement of the hyperons on the nodes of a lattice. For this
purpose, we introduce a simplified model of the hadronic plasma, in which the
nuclear interaction between protons, neutrons and hyperons is mediated by meson
fields. We find that, for some reasonable sets of values of the model
parameters, such ordered phases are energetically favoured as density increases
beyond a threshold value.Comment: 16 pages, 14 figures, submitted to NP
Quantum Communication in Rindler Spacetime
A state that an inertial observer in Minkowski space perceives to be the
vacuum will appear to an accelerating observer to be a thermal bath of
radiation. We study the impact of this Davies-Fulling-Unruh noise on
communication, particularly quantum communication from an inertial sender to an
accelerating observer and private communication between two inertial observers
in the presence of an accelerating eavesdropper. In both cases, we establish
compact, tractable formulas for the associated communication capacities
assuming encodings that allow a single excitation in one of a fixed number of
modes per use of the communications channel. Our contributions include a
rigorous presentation of the general theory of the private quantum capacity as
well as a detailed analysis of the structure of these channels, including their
group-theoretic properties and a proof that they are conjugate degradable.
Connections between the Unruh channel and optical amplifiers are also
discussed.Comment: v3: 44 pages, accepted in Communications in Mathematical Physic
Adsorption of Reactive Particles on a Random Catalytic Chain: An Exact Solution
We study equilibrium properties of a catalytically-activated annihilation reaction taking place on a one-dimensional chain of length () in which some segments (placed at random, with mean concentration
) possess special, catalytic properties. Annihilation reaction takes place,
as soon as any two particles land onto two vacant sites at the extremities
of the catalytic segment, or when any particle lands onto a vacant site on
a catalytic segment while the site at the other extremity of this segment is
already occupied by another particle. Non-catalytic segments are inert with
respect to reaction and here two adsorbed particles harmlessly coexist. For
both "annealed" and "quenched" disorder in placement of the catalytic segments,
we calculate exactly the disorder-average pressure per site. Explicit
asymptotic formulae for the particle mean density and the compressibility are
also presented.Comment: AMSTeX, 27 pages + 4 figure
Space-time evolution and HBT analysis of relativistic heavy ion collisions in a chiral SU(3) x SU(3) model
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at
CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The
dependence of the dynamics and the HBT-parameters on the EoS is studied with
different parametrisations of a chiral SU(3) sigma-omega model. The
selfconsistent collective expansion includes the effects of effective hadron
masses, generated by the nonstrange and strange scalar condensates. Different
chiral EoS show different types of phase transitions and even a crossover. The
influence of the order of the phase transition and of the difference in the
latent heat on the space-time dynamics and pion-HBT radii is studied. A small
latent heat, i.e. a weak first-order chiral phase transition, or even a smooth
crossover leads to distinctly different HBT predictions than a strong first
order phase transition. A quantitative description of the data, both at SPS
energies as well as at RHIC energies, appears difficult to achieve within the
ideal hydrodynamical approach using the SU(3) chiral EoS. A strong first-order
quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT
data from CERN-SPS and BNL-RHIC
Small, Dense Quark Stars from Perturbative QCD
As a model for nonideal behavior in the equation of state of QCD at high
density, we consider cold quark matter in perturbation theory. To second order
in the strong coupling constant, , the results depend sensitively on
the choice of the renormalization mass scale. Certain choices of this scale
correspond to a strongly first order chiral transition, and generate quark
stars with maximum masses and radii approximately half that of ordinary neutron
stars. At the center of these stars, quarks are essentially massless.Comment: ReVTeX, 5 pages, 3 figure
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