9,068 research outputs found
Hybrid stars in the light of the massive pulsar PSR J1614-2230
We perform a systematic study of hybrid star configurations using several
parametrizations of a relativistic mean-field hadronic EoS and the NJL model
for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and
TM1 parametrizations, as well as the very stiff NL3 model. In the NJL
Lagrangian we include scalar, vector and 't Hooft interactions. The vector
coupling constant is treated as a free parameter. We also consider that
there is a split between the deconfinement and the chiral phase transitions
which is controlled by changing the conventional value of the vacuum pressure
in the NJL thermodynamic potential by , being a free parameter. We find that, as we
increase the value of , hybrid stars have a larger maximum
mass but are less stable, i.e. hybrid configurations are stable within a
smaller range of central densities. For large enough , stable
hybrid configurations are not possible at all. The effect of increasing the
coupling constant is very similar. We show that stable hybrid
configurations with a maximum mass larger than the observed mass of the pulsar
PSR J1614-2230 are possible for a large region of the parameter space of
and provided the hadronic equation of state contains nucleons
only. When the baryon octet is included in the hadronic phase, only a very
small region of the parameter space allows to explain the mass of PSR
J1614-2230. We compare our results with previous calculations of hybrid stars
within the NJL model. We show that it is possible to obtain stable hybrid
configurations also in the case that corresponds to the
conventional NJL model for which the pressure and density vanish at zero
temperature and chemical potential.Comment: 7 pages, 5 figures; typos in Table 1 have been correcte
Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models
We investigate the hadron-quark phase transition inside neutron stars and
obtain mass-radius relations for hybrid stars. The equation of state for the
quark phase using the standard NJL model is too soft leading to an unstable
star and suggesting a modification of the NJL model by introducing a momentum
cutoff dependent on the chemical potential. However, even in this approach, the
instability remains. In order to remedy the instability we suggest the
introduction of a vector coupling in the NJL model, which makes the EoS
stiffer, reducing the instability. We conclude that the possible existence of
quark matter inside the stars require high densities, leading to very compact
stars.Comment: 4 pages, 2 figures; prepared for IV International Workshop on
Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200
On the dynamics of bubbles in boiling water
We investigate the dynamics of many interacting bubbles in boiling water by
using a laser scattering experiment. Specifically, we analyze the temporal
variations of a laser intensity signal which passed through a sample of boiling
water. Our empirical results indicate that the return interval distribution of
the laser signal does not follow an exponential distribution; contrariwise, a
heavy-tailed distribution has been found. Additionally, we compare the
experimental results with those obtained from a minimalist phenomenological
model, finding a good agreement.Comment: Accepted for publication in Chaos, Solitons & Fractal
Probing the Ground State and Transition Densities of Halo Nuclei
We investigate the use of elastic and inelastic scatterings with secondary
beams of radioactive nuclei as a mean to obtain information on ground state
properties and transition matrix elements to continuum states. An eikonal model
is developed for this purpose by using the folding potential. In particular we
discuss possible signatures of halo wavefunctions in elastic and inelastic
scattering experiments.Comment: 29 pages, plain Latex. 12 figures available upon request
Symbolic Sequences and Tsallis Entropy
We address this work to investigate symbolic sequences with long-range
correlations by using computational simulation. We analyze sequences with two,
three and four symbols that could be repeated times, with the probability
distribution . For these sequences, we verified that
the usual entropy increases more slowly when the symbols are correlated and the
Tsallis entropy exhibits, for a suitable choice of , a linear behavior. We
also study the chain as a random walk-like process and observe a nonusual
diffusive behavior depending on the values of the parameter .Comment: Published in the Brazilian Journal of Physic
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