Ricardo Flores | Universidad Inca Garcilaso de la Vega (original) (raw)

Papers by Ricardo Flores

Large Scale Structures of the Universe, 1988

XXIV International Conference on High Energy Physics, 1989

Nearly Normal Galaxies, 1987

Physics Letters B, 1989

We calculate the O(a) corrections to the annihilation cross section for dark matter candidates in... more We calculate the O(a) corrections to the annihilation cross section for dark matter candidates in the minimal supersymmetric standard model. In particular, the radiative process )~z~qqg is shown to be at most 15% of the total cross sections (except for very massive binos). We apply our results to the relic abundance of neutralinos left over in the Big Bang. We also comment on the importance of these channels for dark matter annihilation in the galactic halo.

Astrophysical Journal, 1994

The distribution of dark matter around galactic or cluster halos has usually been assumed to be a... more The distribution of dark matter around galactic or cluster halos has usually been assumed to be approximately isothermal with a non-zero core radius, which is expected to be of the order of the size of the visible matter distribution. Recently, the possibility has been raised that dark matter halos might be singular in the sense that the dark matter density could increase monotonically with radius r down to a very small distance from the center of galaxies or clusters. Such central cusps in the dark matter density could lead to a high ux of gamma rays from WIMP dark matter annihilation. Here we analyze two possibilities that have been discussed in the literature, / r n with n 1 or 2, and point out that such density pro les are excluded by gravitional lensing analyses on cluster scales and by the rotation curves of gas-rich, halo-dominated dwarf spirals on small scales. We also point out that if spiral galaxies form by gas infall inside dark matter halos, as they are expected to do in any hierarchical clustering model, such pro les almost always lead to falling rotation curves after infall, contrary to observations.

The Astrophysical Journal, 2000

We present a numerical, hydrodynamical/N-body model of A3266, whose X-ray surface brightness, tem... more We present a numerical, hydrodynamical/N-body model of A3266, whose X-ray surface brightness, temperature distribution, and galaxy spatial-and velocity-distribution data are consistent with the A3266 data. The model is an old (~ 3 Gyr) off-axis merger having a ...

The Astrophysical Journal, 1996

Many multiply{imaged quasars have been found over the years, but none so far with image separatio... more Many multiply{imaged quasars have been found over the years, but none so far with image separation in excess of 8 00 . The absence of such large splittings has been used as a test of cosmological models: the standard Cold Dark Matter model has been excluded on the basis that it predicts far too many large{separation double images. These studies assume that the lensing structure has the mass pro le of a singular isothermal sphere. However, such large splittings would be produced by very massive systems such as clusters of galaxies, for which other gravitational lensing data suggest less singular mass pro les. Here we analyze two cases of mass pro les for lenses: an isothermal sphere with a nite core radius (density / (r 2 +r 2 core ) 1 ), and a Hernquist pro le ( / r 1 (r + a) 3 ). We nd that small core radii r core 30h 1 kpc, as suggested by the cluster data, or large a > 300h 1 kpc, as needed for compatibility with gravitational distortion data, would reduce the number of large{angle splittings by an order of magnitude or more. Thus, it appears that these tests are sensitive both to the cosmological model (number density of lenses) and to the inner lens structure, which is unlikely to depend sensitively on the cosmology, making it di cult to test the cosmological models by large{separation quasar lensing until we reliably know the structure of the lenses themselves.

Physics Letters B, 1990

The lightest neutralino is a natural candidate for the dark matter in the Universe. It is very ne... more The lightest neutralino is a natural candidate for the dark matter in the Universe. It is very nearly a pure bino or a symmetric or antisymmetric higgsino over a wide region of parameter space of the supersymmetric standard model. We consider here their elastic scattering off ...

Physics Letters B, 1988

Motivated by current interest in searches for products of halo and solar annihilation of dark mat... more Motivated by current interest in searches for products of halo and solar annihilation of dark matter particles, as well as its direct detection, we discuss the range of likely values of the density of halo dark matter (DM) in the solar neighbourhood, p~M calculated using a model that assumes that the radial distribution of DM in protogalaxies changes adiabatically as the gas fails toward the centre to form the visible cores, lfprotogalaxies have the structure expected in the cold DM cosmology, we argue that a variety of observational and theoretical constraints imply 0.2 < p ~M/GeV cm-3 < 0.43 and that the luminous matter mass fraction F< 0.12.

The Astrophysical Journal, 1997

Spheroidal components of spiral galaxies have been considered the only dynamically important comp... more Spheroidal components of spiral galaxies have been considered the only dynamically important component in gravitational lensing studies thus far. Here we point out that including the disk component can have a significant effect, depending on the disk inclination, on a variety of lensing properties that are relevant to present studies and future surveys. As an example, we look at the multiple image system B1600+434, recently identified as being lensed by a spiral galaxy. We find that including the disk component one can understand the fairly large image separation as being due to the inclination of a typical spiral, rather than the presence of a very massive halo. The fairly low magnification ratio can also be readily understood if the disk is included. We also discuss how such lensed systems might allow one to constrain parameters of spiral galaxies such as a disk-to-halo mass ratio, and disk mass scale length. Another example we consider is the quasar multiple-lensing cross section, which we find can increase many-fold at high inclination for a typical spiral. Finally, we discuss the changes in the gravitational lensing effects on damped Lyman alpha systems (DLAS) when disk lensing is included.

Astrophysical Journal, 1993

A simple analytic mode of the response of dark matter halos to the dissipative infall of the lumi... more A simple analytic mode of the response of dark matter halos to the dissipative infall of the luminous material to form an exponential disk is used to explore the dependence of the final rotation curves on all the relevant parameters: the ratio of the dissipative baryonic mass to the total galaxy mass, including dark matter; the ratio of the disk exponential scale length to the truncation radius; the core radius of the isothermal halo in the absence of dissipation; and the dimensionless angular momentum parameter. Particular attention is given to the final rotation curves expected in the tidal torque theory of angular momentum, in which (lambda) is about 0.05. For F of about 0.05 the dispersion in lambda expected in the tidal torque theory, 0.02-0.1, leads to rotation curves for bright galaxies whose systematics are much like those of galaxies for which H I data are available when consistent baryonic disk-scale lengths are used throughout. The mass inside R(H) exhibits a spread of values consistent with observations except possibly for the smallest galaxies, which may have suffered significant loss.

Monthly Notices of …, 2006

Using six high resolution dissipationless simulations with a varying box size in a flat LCDM univ... more Using six high resolution dissipationless simulations with a varying box size in a flat LCDM universe, we study the mass and redshift dependence of dark matter halo shapes for M vir = 9.0 × 10 11 − 2.0 × 10 14 , over the redshift range z = 0 − 3, and for two values of σ 8 = 0.75 and 0.9. Remarkably, we find that the redshift, mass, and σ 8 dependence of the mean smallest-to-largest axis ratio of halos is well described by the simple power-law relation s = (0.54 ± 0.02)(M vir /M * ) −0.050±0.003 , where s is measured at 0.3R vir and the z and σ 8 dependences are governed by the characteristic nonlinear mass, M * = M * (z, σ 8 ). We find that the scatter about the mean s is well described by a Gaussian with σ ∼ 0.1, for all masses and redshifts. We compare our results to a variety of previous works on halo shapes and find that reported differences between studies are primarily explained by differences in their methodologies. We address the evolutionary aspects of individual halo shapes by following the shapes of the halos through ∼ 100 snapshots in time. We determine the formation scalefactor a c as defined by and find that it can be related to the halo shape at z = 0 and its evolution over time.

Physics Letters B, 1991

We survey the elastic scattering rates of neutralinos on many nuclei, incorporating LEP constrain... more We survey the elastic scattering rates of neutralinos on many nuclei, incorporating LEP constraints and choosing model parameters that give a critical density of the lightest neutralino, using the odd-group model to estimate nuclear matrix elements and incorporating a simple model for the momentum dependence of the elastic spin and mass form factors. We find that the rates for elastic scattering on 19F can be estimated reliably and are reasonably large for a relic mass, Mx, in the range M~ 20-60 GeV. We present calculations of the elastic neutralino -~9F scattering rates in regions of parameter space consistent with LEP and other laboratory experiments.