2,649 research outputs found
A closer look at the Yukawa's interaction from a symmetry group perspective
I investigate the use of the SU(3) Clebsch-Gordan coefficients in light of
the relations of completeness and closure. I show that in the case of 1, there is an additional interaction: the exchange of a
meson between a and a hyperon that only affects the
symmetric coupling. I then calculate these additional coupling constants and
show that this recovers the completeness and closure of the SU(3)
Clebsch-Gordan coefficients for all values of . Besides, it increases
the symmetry of the theory, once now we can group the baryon octet into four
doublets. Finally, I add the new coupling constants to study numerical results
in the hyperon onset in dense nuclear matter assuming as a free
parameter.Comment: 16 pages, published versio
Gravitational Wave Signatures of Highly Magnetized Neutron Stars
Motivated by the recent gravitational wave detection by the LIGO-VIRGO
observatories, we study the Love number and dimensionless tidal polarizability
of highly magnetized stars. We also investigate the fundamental quasi-normal
mode of neutron stars subject to high magnetic fields. To perform our
calculations we use the chaotic field approximation and consider both nucleonic
and hyperonic stars. As far as the fundamental mode is concerned, we conclude
that the role played by the constitution of the stars is far more relevant than
the intensity of the magnetic field and if massive stars are considered, the
ones constituted by nucleons only present frequencies somewhat lower than the
ones with hyperonic cores, a feature that can be used to point out the real
internal structure of neutron stars. Moreover, our studies clearly indicate
that strong magnetic fields play a crucial role in the deformability of low
mass neutron stars, with possible consequences on the interpretation of the
detected gravitational waves signatures.Comment: 24 pages, 4 figures, 6 table
Anisotropic Strange Stars in the Spotlight: Unveiling Constraints through Observational Data
Motivated by the recent suggestions that very massive and very light compact
objects exist, in this letter we revisit the possibility of such objects being
strange stars instead of the standard hadronic neutron stars. We study the
possible presence of local anisotropy and how it affects the macroscopic
properties of strange stars and compare our results with the recent constraints
presented in the literature. We found that the presence of anisotropy increases
the maximum mass, the radius of the canonical star, and its tidal deformability
for positive values of , and the opposite for negative
values. We also show that some observational constraints that are in conflict
with the theory of standard hadronic neutron stars, can easily be taken into
account considering strange stars.Comment: 5 pages, 2 figures, 1 table, comments are welcom
The baryon coupling scheme in an unified SU(3) and SU(6) symmetry formalism
We calculate the baryon-meson coupling constants for the spin-1/2 baryonic
octet and spin-3/2 decuplet in a unified approach relying on symmetry arguments
such as the fact that the Yukawa couplings, present in the Lagrangian density
of the Walecka-type models, must be an invariant under SU(3) and SU(6) group
transformations. The coupling constants of the baryon with the scalar
meson are fixed to reproduce the known potential depths for the hyperons and
resonances, in an approach that can be extended to all particles. We
then apply the calculated coupling constants to study neutron star matter with
hyperons and deltas admixed to its composition. We conclude that the
is by far the most important exotic particle that can be present in the neutron
star interior. It is always present, independent of the chosen
parameterization, and might appear in almost every known neutron star, once its
onset happens at very low density. Yet, its presence affects the astrophysical
properties of the canonical 1.4 M star, and, in some cases, it can even
contribute to an increase in the maximum mass reached.Comment: 16 pages, 11 figures, 5 table
Evidence for a role of nitric oxide in hindlimb vasodilation induced by hypothalamic stimulation in anesthetized rats
Electrical stimulation of the hypothalamus produces cardiovascular adjustments consisting of hypertension, tachycardia, visceral vasoconstriction and hindlimb vasodilation. Previous studies have demonstrated that hindlimb vasodilation is due a reduction of sympathetic vasoconstrictor tone and to activation of beta2-adrenergic receptors by catecholamine release. However, the existence of a yet unidentified vasodilator mechanism has also been proposed. Recent studies have suggested that nitric oxide (NO) may be involved. The aim of the present study was to investigate the role of NO in the hindquarter vasodilation in response to hypothalamic stimulation. In pentobarbital-anesthetized rats hypothalamic stimulation (100 Hz, 150µA, 6 s) produced hypertension, tachycardia, hindquarter vasodilation and mesenteric vasoconstriction. Alpha-adrenoceptor blockade with phentolamine (1.5 mg/kg, iv) plus bilateral adrenalectomy did not modify hypertension, tachycardia or mesenteric vasoconstriction induced by hypothalamic stimulation. Hindquarter vasodilation was strongly reduced but not abolished. The remaining vasodilation was completely abolished after iv injection of the NOS inhibitor L-NAME (20 mg/kg, iv). To properly evaluate the role of the mechanism of NO in hindquarter vasodilation, in a second group of animals L-NAME was administered before alpha-adrenoceptor blockade plus adrenalectomy. L-NAME treatment strongly reduced hindquarter vasodilation in magnitude and duration. These results suggest that NO is involved in the hindquarter vasodilation produced by hypothalamic stimulation.Em animais anestesiados a EE do hipotálamo produz um padrão de ajustes cardiovasculares caracterizado por hipertensão arterial, taquicardia, vasodilatação muscular e vasoconstrição mesentérica, entretanto, os mecanismos periféricos envolvidos nestes ajustes cardiovasculares ainda não foram completamente esclarecidos. O presente estudo teve como objetivo caracterizar os mecanismos periféricos responsáveis pela redistribuição de fluxo sanguíneo produzidas pela EE do hipotálamo. Os resultados obtidos demonstraram que 1) em ratos anestesiados a EE do hipotálamo produziu hipertensão arterial, taquicardia, vasoconstrição no leito mesentérico e acentuada vasodilatação dos membros posteriores; 2) a combinação do bloqueio farmacológico de receptores alfa1 e alfa2 adrenérgicos com fentolamina mais adrenalectomia bilateral reduziu a vasoconstrição mesentérica e a vasodilatação dos membros posteriores. Nestes animais o bloqueio da síntese de NO com L-NAME provocou nova redução significante da vasodilatação dos membros posteriores; 3) a administração de L-NAME, previamente o bloqueio farmacológico com fentolamina mais adrenalectomia bilateral, reduziu as respostas de vasoconstrição mesentérica e de vasodilatação dos membros posteriores. Estes resultados sugerem a existência de pelo menos três possíveis mecanismos responsáveis pela vasodilatação dos membros posteriores induzida pela EE do hipotálamo: 1) ativação de receptores beta-adrenérgicos por catecolaminas liberadas pela medula adrenal; 2) redução do tono vasoconstritor simpático e 3) um terceiro mecanismo que utiliza NO como mediador.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNIFESP-EPM Departamento de FisiologiaUNIFESP, EPM, Depto. de FisiologiaSciEL
Dark matter effects on hybrid star properties
In the present work we investigate the effects of dark matter (DM) on hybrid
star properties. We assume that dark matter is mixed with both hadronic and
quark matter and interact with them through the exchange of a Higgs boson. The
hybrid star properties are obtained from equations of state calculated with a
Maxwell prescription. For the hadronic matter we use the NL3* parameter set and
for the quark matter, the MIT bag model with a vector interaction. We see that
dark matter does not influence the phase transition points (pressure and
chemical potential) but shifts the discontinuity on the energy density, which
ultimately reduces the minimum mass star that contains a quark core. Moreover,
it changes considerably the star family mass-radius diagrams and moves the
merger polarizability curves inside the confidence lines. Another interesting
feature is the influence of DM in the quark core of the hybrid stars
constructed. Our results show an increase of the core radius for higher values
of the dark particle Fermi momentum
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