110 research outputs found

### Quark deconfinement transition in neutron stars with the field correlator method

A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. In this article, we perform a study of the hadron--quark phase transition in cold ($T = 0$) neutron star matter and we calculate various structural properties of hybrid stars. For the quark phase, we make use of an equation of state (EOS) derived with the Field Correlator Method (FCM) recently extended to the case of nonzero baryon density. For the hadronic phase, we consider both pure nucleonic and hyperonic matter, and we derive the corresponding EOS within a relativistic mean field approach. We make use of measured neutron star masses, and particularly the mass $M = 1.97 \pm 0.04 \, M_\odot$ of PSR~J1614-2230, to constrain the values of the gluon condensate $G_2$, which is one of the EOS parameter within the FCM. We find that the values of $G_2$ extracted from the mass measurement of PSR~J1614-2230 are consistent with the values of the same quantity derived, within the FCM, from recent lattice QCD calculations of the deconfinement transition temperature at zero baryon chemical potential. The FCM thus provides a powerful tool to link numerical calculations of QCD on a space-time lattice with measured neutron star masses

### Constraints on microscopic and phenomenological equations of state of dense matter from GW170817

We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the Î˛-stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary's component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data

### Chiral model approach to quark matter nucleation in neutron stars

The nucleation process of quark matter in both cold and hot dense hadronic
matter is investigated using a chiral approach to describe the quark phase. We
use the Nambu-Jona-Lasinio and the Chromo Dielectric models to describe the
deconfined phase and the non-linear Walecka model for the hadronic one. The
effect of hyperons on the transition phase between hadronic and quark matter is
studied. The consequences of the nucleation process for neutron star physics
are outlined

### Theoretical study of the d(d,p)3H and d(d,n)3He processes at low energies

We present a theoretical study of the processes d(d,p)3H and d(d,n)3He at
energies of interest for energy production and for big-bang nucleosynthesis. We
accurately solve the four body scattering problem using the ab-initio
hyperspherical harmonic method, starting from nuclear Hamiltonians which
include modern two- and three-nucleon interactions, derived in chiral effective
field theory. We report results for the astrophysical factor, the quintet
suppression factor, and various single and double polarized observables. An
estimate of the "theoretical uncertainty" for all these quantities is provided
by varying the cutoff parameter used to regularize the chiral interactions at
high momentum.Comment: 5 pages, 4 figure

### Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot $\beta$-stable
hadronic matter. Assuming a first order phase transition, we calculate the
enthalpy per baryon of the hadron-quark phase transition. We calculate and
compare the nucleation rate and the nucleation time due to thermal and quantum
nucleation mechanisms. We compute the crossover temperature above which thermal
nucleation dominates the finite temperature quantum nucleation mechanism. We
next discuss the consequences for the physics of proto-neutron stars. We
introduce the concept of limiting conversion temperature and critical mass
$M_{cr}$ for proto-hadronic stars, and we show that proto-hadronic stars with a
mass $M < M_{cr}$ could survive the early stages of their evolution without
decaying to a quark star

### PT-symmetry breaking in complex nonlinear wave equations and their deformations

We investigate complex versions of the Korteweg-deVries equations and an Ito
type nonlinear system with two coupled nonlinear fields. We systematically
construct rational, trigonometric/hyperbolic, elliptic and soliton solutions
for these models and focus in particular on physically feasible systems, that
is those with real energies. The reality of the energy is usually attributed to
different realisations of an antilinear symmetry, as for instance PT-symmetry.
It is shown that the symmetry can be spontaneously broken in two alternative
ways either by specific choices of the domain or by manipulating the parameters
in the solutions of the model, thus leading to complex energies. Surprisingly
the reality of the energies can be regained in some cases by a further breaking
of the symmetry on the level of the Hamiltonian. In many examples some of the
fixed points in the complex solution for the field undergo a Hopf bifurcation
in the PT-symmetry breaking process. By employing several different variants of
the symmetries we propose many classes of new invariant extensions of these
models and study their properties. The reduction of some of these models yields
complex quantum mechanical models previously studied.Comment: 50 pages, 39 figures (compressed in order to comply with arXiv
policy; higher resolutions maybe obtained from the authors upon request

### Numerical analysis of the resistance behavior of an electrostatically-induced graphene double junction

We present a numerical approach that we have developed in order to reproduce and explain the resistance behavior recently observed, as a function of the backgate voltage and of the position of a biased scanning probe, in a graphene flake in which a double p-n junction has been electrostatically induced. A simplified electrostatic model has been adopted to simulate the effect of gate voltages on the potential landscape, assuming for it a slow variation in space and using a simple capacitive model for the coupling between the electrodes and the graphene sheet. The transport analysis has then been performed with a solution of the Dirac equation in the reciprocal space coupled with a recursive scattering matrix approach. The efficiency of the adopted numerical procedure has allowed us to explore a wide range of possible potential landscapes and bias points, with the result of achieving a good agreement with available experimental data

### Effects of quark matter nucleation on the evolution of proto-neutron stars

(Abridged) A phase of strong interacting matter with deconfined quarks is
expected in the core of massive neutron stars. If this deconfinement phase
transition is of the first order then it will be triggered by the nucleation of
a critical size drop of the stable quark phase in the metastable hadronic
phase. Within these circumstances it has been shown that cold pure hadronic
compact stars above a threshold value of their gravitational mass are
metastable with respect to the "decay" to quark stars (compact stars made at
least in part of quark matter). This stellar conversion process liberates a
huge amount of energy, and it could be the energy source of some of the long
GRBs. The main goal of the present work is to establish whether a newborn
hadronic star (proto-hadronic star) could survive the early stages of its
evolution without "decaying" to a quark star. To this aim, we study the
nucleation process of quark matter in hot beta-stable hadronic matter, with and
without trapped neutrinos. We calculate and compare the nucleation rate and the
nucleation time due to thermal and quantum nucleation mechanisms. We compute
the crossover temperature above which thermal nucleation dominates the finite
temperature quantum nucleation mechanism. We next discuss the consequences of
quark matter nucleation for the physics and the evolution of proto-neutron
stars. We introduce the new concept of limiting conversion temperature and
critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic
stars with a mass M < M_cr could survive the early stages of their evolution
without decaying to a quark star. We extend the concept of maximum mass of a
"neutron star" with respect to the classical one introduced by Oppenheimer &
Volkoff to account for the existence of two distinct families of compact stars
(hadronic stars and quark stars) as predicted by the present scenario.Comment: Accepted for publication in Astronomy and Astrophysic

### Unraveling quantum Hall breakdown in bilayer graphene with scanning gate microscopy

We use low-temperature scanning gate microscopy (SGM) to investigate the
breakdown of the quantum Hall regime in an exfoliated bilayer graphene flake.
SGM images captured during breakdown exhibit intricate patterns of "hotspots"
where the conductance is strongly affected by the presence of the tip. Our
results are well described by a model based on quantum percolation which
relates the points of high responsivity to tip-induced scattering between
localized Landau levels.Comment: 6 pages, 4 figure

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