89 research outputs found
Outskirts of Distant Galaxies In Absorption
QSO absorption spectroscopy provides a sensitive probe of both the neutral
medium and diffuse ionized gas in the distant Universe. It extends 21cm maps of
gaseous structures around low-redshift galaxies both to lower gas column
densities and to higher redshifts. Combining galaxy surveys with
absorption-line observations of gas around galaxies enables comprehensive
studies of baryon cycles in galaxy outskirts over cosmic time. This Chapter
presents a review of the empirical understanding of the cosmic neutral gas
reservoir from studies of damped Lya absorbers (DLAs). It describes the
constraints on the star formation relation and chemical enrichment history in
the outskirts of distant galaxies from DLA studies. A brief discussion of
available constraints on the ionized circumgalactic gas from studies of lower
column density Lya absorbers and associated ionic absorption transitions is
presented at the end.Comment: 45 pages, 7 figures, invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Leptogenesis and low energy observables in left-right symmetric models
In the context of left-right symmetric models we study the connection of
leptogenesis and low energy parameters such as neutrinoless double beta decay
and leptonic CP violation. Upon imposition of a unitarity constraint, the
neutrino parameters are significantly restricted and the Majorana phases are
determined within a narrow range, depending on the kind of solar solution. One
of the Majorana phases gets determined to a good accuracy and thereby the
second phase can be probed from the results of neutrinoless double beta decay
experiments. We examine the contributions of the solar and atmospheric mass
squared differences to the asymmetry and find that in general the solar scale
dominates. In order to let the atmospheric scale dominate, some finetuning
between one of the Majorana phases and the Dirac CP phase is required. In this
case, one of the Majorana phases is determined by the amount of CP violation in
oscillation experiments.Comment: 18 pages, 6 figures. Matches version to appear in PR
Computation of the winding number diffusion rate due to the cosmological sphaleron
A detailed quantitative analysis of the transition process mediated by a
sphaleron type non-Abelian gauge field configuration in a static Einstein
universe is carried out. By examining spectra of the fluctuation operators and
applying the zeta function regularization scheme, a closed analytical
expression for the transition rate at the one-loop level is derived. This is a
unique example of an exact solution for a sphaleron model in spacetime
dimensions.Comment: Some style corrections suggested by the referee are introduced
(mainly in Sec.II), one reference added. To appear in Phys.Rev.D 29 pages,
LaTeX, 3 Postscript figures, uses epsf.st
Strange quark matter in a chiral SU(3) quark mean field model
We apply the chiral SU(3) quark mean field model to investigate strange quark
matter. The stability of strange quark matter with different strangeness
fraction is studied. The interaction between quarks and vector mesons
destabilizes the strange quark matter. If the strength of the vector coupling
is the same as in hadronic matter, strangelets can not be formed. For the case
of beta equilibrium, there is no strange quark matter which can be stable
against hadron emission even without vector meson interactions.Comment: 19 pages, 8 figure
Large Nc and Chiral Dynamics
We study the dependence on the number of colors of the leading pi pi
scattering amplitude in chiral dynamics. We demonstrate the existence of a
critical number of colors for and above which the low energy pi pi scattering
amplitude computed from the simple sum of the current algebra and vector meson
terms is crossing symmetric and unitary at leading order in a truncated and
regularized 1/Nc expansion. The critical number of colors turns out to be Nc=6
and is insensitive to the explicit breaking of chiral symmetry.
Below this critical value, an additional state is needed to enforce the
unitarity bound; it is a broad one, most likely of "four quark" nature.Comment: RevTeX4, 6 fig., 5 page
In search of the QCD-Gravity correspondence
Quantum Chromodynamics (QCD) is the fundamental theory of strong
interactions. It describes the behavior of quarks and gluons which are the
smallest known constituents of nuclear matter. The difficulties in solving the
theory at low energies in the strongly interacting, non-perturbative regime
have left unanswered many important questions in QCD, such as the nature of
confinement or the mechanism of hadronization. In these lectures oriented
towards the students we introduce two classes of dualities that attempt to
reproduce many of the features of QCD, while making the treatment at strong
coupling more tractable: (1) the AdS/CFT correspondence between a specific
class of string theories and a conformal field theory and (2) an effective
low-energy theory of QCD dual to classical QCD on a curved conformal
gravitational background. The hope is that by applying these dualities to the
evaluation of various properties of the strongly-interacting matter produced in
heavy ion collisions one can understand how QCD behaves at strong coupling. We
give an outline of the applications, with emphasis on two transport
coefficients of QCD matter -- shear and bulk viscosities.Comment: 31 pages, 7 figures; Lectures delivered by D. Kharzeev at the
International QGP Winter School, Jaipur, India, February 1-3, 200
Far-Ultraviolet and Far-Infrared Bivariate Luminosity Function of Galaxies: Complex Relation between Stellar and Dust Emission
Far-ultraviolet (FUV) and far-infrared (FIR) luminosity functions (LFs) of
galaxies show a strong evolution from to , but the FIR LF
evolves much stronger than the FUV one. The FUV is dominantly radiated from
newly formed short-lived OB stars, while the FIR is emitted by dust grains
heated by the FUV radiation field. It is known that dust is always associated
with star formation activity. Thus, both FUV and FIR are tightly related to the
star formation in galaxies, but in a very complicated manner. In order to
disentangle the relation between FUV and FIR emissions, we estimate the UV-IR
bivariate LF (BLF) of galaxies with {\sl GALEX} and {\sl AKARI} All-Sky Survey
datasets. Recently we invented a new mathematical method to construct the BLF
with given marginals and prescribed correlation coefficient. This method makes
use of a tool from mathematical statistics, so called "copula". The copula
enables us to construct a bivariate distribution function from given marginal
distributions with prescribed correlation and/or dependence structure. With
this new formulation and FUV and FIR univariate LFs, we analyze various FUV and
FIR data with {\sl GALEX}, {\sl Spitzer}, and {\sl AKARI} to estimate the UV-IR
BLF. The obtained BLFs naturally explain the nonlinear complicated relation
between FUV and FIR emission from star-forming galaxies. Though the faint-end
of the BLF was not well constrained for high- samples, the estimated linear
correlation coefficient was found to be very high, and is remarkably
stable with redshifts (from 0.95 at to 0.85 at ). This implies
the evolution of the UV-IR BLF is mainly due to the different evolution of the
univariate LFs, and may not be controlled by the dependence structure.Comment: 10 pages, 7 figures, Earth, Planets and Space, in pres
Partial Deconfinement in Color Superconductivity
We analyze the fate of the unbroken SU(2) color gauge interactions for 2
light flavors color superconductivity at non zero temperature. Using a simple
model we compute the deconfining/confining critical temperature and show that
is smaller than the critical temperature for the onset of the superconductive
state itself. The breaking of Lorentz invariance, induced already at zero
temperature by the quark chemical potential, is shown to heavily affect the
value of the critical temperature and all of the relevant features related to
the deconfining transition. Modifying the Polyakov loop model to describe the
SU(2) immersed in the diquark medium we argue that the deconfinement transition
is second order. Having constructed part of the equation of state for the 2
color superconducting phase at low temperatures our results are relevant for
the physics of compact objects featuring a two flavor color superconductive
state.Comment: 9 pp, 4 eps-figs, version to appear in PR
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Probing the seesaw mechanism with neutrino data and leptogenesis
In the framework of the seesaw mechanism with three heavy right-handed
Majorana neutrinos and no Higgs triplets we carry out a systematic study of the
structure of the right-handed neutrino sector. Using the current low-energy
neutrino data as an input and assuming hierarchical Dirac-type neutrino masses
, we calculate the masses and the mixing of the heavy neutrinos.
We confront the inferred properties of these neutrinos with the constraints
coming from the requirement of a successful baryogenesis via leptogenesis. In
the generic case the masses of the right-handed neutrinos are highly
hierarchical: ; the lightest mass is GeV and the generated baryon-to-photon ratio is
much smaller than the observed value. We find the special cases which
correspond to the level crossing points, with maximal mixing between two
quasi-degenerate right-handed neutrinos. Two level crossing conditions are
obtained: (1-2 crossing) and (2-3
crossing), where and are respectively the 11-entry and the
12-subdeterminant of the light neutrino mass matrix in the basis where the
neutrino Yukawa couplings are diagonal. We show that sufficient lepton
asymmetry can be produced only in the 1-2 crossing where GeV, GeV and .Comment: 30 pages, 2 eps figures, JHEP3.cls, typos corrected, note (and
references) added on non-thermal leptogenesi
- âŠ