942 research outputs found
On the core-halo distribution of dark matter in galaxies
We investigate the distribution of dark matter in galaxies by solving the
equations of equilibrium of a self-gravitating system of massive fermions
(`inos') at selected temperatures and degeneracy parameters within general
relativity. Our most general solutions show, as a function of the radius, a
segregation of three physical regimes: 1) an inner core of almost constant
density governed by degenerate quantum statistics; 2) an intermediate region
with a sharply decreasing density distribution followed by an extended plateau,
implying quantum corrections; 3) an asymptotic, classical
Boltzmann regime fulfilling, as an eigenvalue problem, a fixed value of the
flat rotation curves. This eigenvalue problem determines, for each value of the
central degeneracy parameter, the mass of the ino as well as the radius and
mass of the inner quantum core. Consequences of this alternative approach to
the central and halo regions of galaxies, ranging from dwarf to big spirals,
for SgrA*, as well as for the existing estimates of the ino mass, are outlined.Comment: 8 pages, 5 figures. Accepted for publication by MNRA
Novel constraints on fermionic dark matter from galactic observables I: The Milky Way
We have recently introduced a new model for the distribution of dark matter
(DM) in galaxies based on a self-gravitating system of massive fermions at
finite temperatures, the Ruffini-Arg\"uelles-Rueda (RAR) model. We show that
this model, for fermion masses in the keV range, explains the DM halo of the
Galaxy and predicts the existence of a denser quantum core at the center. We
demonstrate here that the introduction of a cutoff in the fermion phase-space
distribution, necessary to account for the finite Galaxy size, defines a new
solution with a central core which represents an alternative to the black hole
(BH) scenario for SgrA*. For a fermion mass in the range --
~keV, the DM halo distribution is in agreement with the Milky Way rotation
curve data, while harbors a dense quantum core of about
within the S2-star pericenter.Comment: 11 pages, 5 figures. Published in Physics of the Dark Univers
The role of self-interacting right-handed neutrinos in galactic structure
It has been shown previously that the DM in galactic halos can be explained
by a self-gravitating system of massive keV fermions (`inos') in thermodynamic
equilibrium, and predicted the existence of a denser quantum core of inos
towards the center of galaxies. In this article we show that the inclusion of
self-interactions among the inos, modeled within a relativistic
mean-field-theory approach, allows the quantum core to become massive and
compact enough to explain the dynamics of the S-cluster stars closest to the
Milky Way's galactic center. The application of this model to other galaxies
such as large elliptical harboring massive central dark objects of is also investigated. We identify these interacting inos with sterile
right-handed neutrinos pertaining to minimal extensions of the Standard Model,
and calculate the corresponding total cross-section within an
electroweak-like formalism to be compared with other observationally inferred
cross-section estimates. The coincidence of an ino mass range of few tens of
keV derived here only from the galactic structure, with the range obtained
independently from other astrophysical and cosmological constraints, points
towards an important role of the right-handed neutrinos in the cosmic
structure.Comment: 33 pages, 9 figures, version to appear in JCA
Hernia perineal en el perro. Combinación de tres técnicas para la corrección quirúrgica. Tres casos clínicos
En este trabajo se presentan cuatro cirugías de hernia perineal en el perro, realizadas con una combinación de tres técnicas: elevación del músculo obturador interno, interposición de una malla de polipropileno y transposición con rotación del músculo glúteo superficial. Con esta combinación de técnicas intentamos asegurar el menor índice de recidivas a largo plazo posible. También realizamos una aproximación a la controvertida etiología de este problema, todavía no suficientemente aclarada, pero sí orientada hacia una predisposición genética que alteraría la función de los receptores androgénicos en la musculatura del diafragma pélvico. Discutimos las alternativas quirúrgicas y tratamientos complementarios como la orquiectomía.
Strong lensing by fermionic dark matter in galaxies
It has been shown that a self-gravitating system of massive keV fermions in
thermodynamic equilibrium correctly describes the dark matter (DM) distribution
in galactic halos and predicts a denser quantum core towards the center of the
configuration. Such a quantum core, for a fermion mass in the range of keV
keV, can be an alternative interpretation of the
central compact object in Sgr A*. We present in this work the gravitational
lensing properties of this novel DM model in Milky Way-like spiral galaxies. We
describe the lensing effects of the pure DM component both on halo scales,
where we compare them to the effects of the Navarro-Frenk-White and the
Non-Singular Isothermal Sphere DM models, and near the galaxy center, where we
compare them with the effects of a Schwarzschild BH. For the particle mass
leading to the most compact DM core, keV, we draw the
following conclusions. At distances pc from the center of the
lens the effect of the central object on the lensing properties is negligible.
However, we show that measurements of the deflection angle produced by the DM
distribution in the outer region at a few kpc, together with rotation curve
data, could help to discriminate between different DM models. We show that at
distances pc strong lensing effects, such as multiple images and
Einstein rings, may occur. Large differences in the deflection angle produced
by a DM central core and a central BH appear at distances
pc; in this regime the weak-field formalism is no longer applicable and the
exact general-relativistic formula has to be used. We find that quantum DM
cores do not show a photon sphere what implies that they do not cast a shadow.
Similar conclusions apply to the other DM distributions for other fermion
masses in the above specified range and for other galaxy types.Comment: 10 pages, 8 figures. v2: Version published in PR
Ectopia ureteral bilateral intra y extra mural : caso clínico
La ectopia ureteral es una malformación congénita consistente en una apertura errónea del uréter que sobre pasa la vejiga urinaria y termina en otro lugar. Se presenta con mucha mayor frecuencia en hembras y hay algunas razas predispuestas como el Husky siberiano, el Caniche o el Retriever. En la práctica clínica se distinguen 3 situaciones: ectopia extramural a uretra, ectopia intramural y ectopia a útero. Describimos un caso clínico en el que se dio un tipo de uréter ectópico diferente en cada uréter, intramural el derecho y extramural el izquierdo.
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