51,948 research outputs found
Effective operator contributions to the oblique parameters
We present a model and process independent study of the contributions from
non-Standard Model physics to the oblique parameters S, T and U. We show that
within an effective lagrangian parameterization the expressions for the oblique
parameters in terms of observables are consistent, while those in terms of the
vector-boson vacuum polarization tensors are ambiguous. We obtain the
constraints on the scale of new physics derived from current data on S, T and U
and note that deviations in U from its Standard Model value would favor a
scenario where the underlying physics does not decouple.Comment: 13 pages, RevTe
Improving the precision matrix for precision cosmology
The estimation of cosmological constraints from observations of the large
scale structure of the Universe, such as the power spectrum or the correlation
function, requires the knowledge of the inverse of the associated covariance
matrix, namely the precision matrix, . In most analyses,
is estimated from a limited set of mock catalogues. Depending
on how many mocks are used, this estimation has an associated error which must
be propagated into the final cosmological constraints. For future surveys such
as Euclid and DESI, the control of this additional uncertainty requires a
prohibitively large number of mock catalogues. In this work we test a novel
technique for the estimation of the precision matrix, the covariance tapering
method, in the context of baryon acoustic oscillation measurements. Even though
this technique was originally devised as a way to speed up maximum likelihood
estimations, our results show that it also reduces the impact of noisy
precision matrix estimates on the derived confidence intervals, without
introducing biases on the target parameters. The application of this technique
can help future surveys to reach their true constraining power using a
significantly smaller number of mock catalogues.Comment: 9 pages, 7 figures, minor changes to match version accepted by MNRA
Galaxy phase-space density data exclude Bose-Einstein condensate Axion Dark Matter
Light scalars (as the axion) with mass m ~ 10^{-22} eV forming a
Bose-Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were
therefore proposed as dark matter (DM) candidates. Our treatment here is
generic, independent of the particle physics model and applies to all DM BEC,
in or out of equilibrium. Two observed quantities crucially constrain DM in an
inescapable way: the average DM density rho_{DM} and the phase-space density Q.
The observed values of rho_{DM} and Q in galaxies today constrain both the
possibility to form a BEC and the DM mass m. These two constraints robustly
exclude axion DM that decouples just after the QCD phase transition. Moreover,
the value m ~ 10^{-22} eV can only be obtained with a number of
ultrarelativistic degrees of freedom at decoupling in the trillions which is
impossible for decoupling in the radiation dominated era. In addition, we find
for the axion vacuum misalignment scenario that axions are produced strongly
out of thermal equilibrium and that the axion mass in such scenario turns to be
17 orders of magnitude too large to reproduce the observed galactic structures.
Moreover, we also consider inhomogenous gravitationally bounded BEC's supported
by the bosonic quantum pressure independently of any particular particle
physics scenario. For a typical size R ~ kpc and compact object masses M ~ 10^7
Msun they remarkably lead to the same particle mass m ~ 10^{-22} eV as the BEC
free-streaming length. However, the phase-space density for the gravitationally
bounded BEC's turns to be more than sixty orders of magnitude smaller than the
galaxy observed values. We conclude that the BEC's and the axion cannot be the
DM particle. However, an axion in the mili-eV scale may be a relevant source of
dark energy through the zero point cosmological quantum fluctuations.Comment: 8 pages, no figures. Expanded versio
Warm Dark Matter Galaxies with Central Supermassive Black-Holes
We generalize the Thomas-Fermi approach to galaxy structure to include
self-consistently and non-linearly central supermassive black holes. This
approach naturally incorporates the quantum pressure of the warm dark matter
(WDM) particles and shows its full powerful and clearness in the presence of
supermassive black holes (SPMHs). We find the main galaxy and central black
hole magnitudes: halo radius r_h , halo mass M_h, black hole mass M_BH,
velocity dispersion, phase space density, with their realistic astrophysical
values, masses and sizes over a wide galaxy range. The SMBH masses arise
naturally in this framework. Our extensive numerical calculations and detailed
analytic resolution show that with SMBH's, both WDM regimes: classical
(Boltzmann dilute) and quantum (compact) do necessarily co-exist in any galaxy:
from the smaller and compact galaxies to the largest ones. The transition from
the quantum to the classical region occurs precisely at the same point r_A
where the chemical potential vanishes. A novel halo structure with three
regions shows up: A small quantum compact core of radius r_A around the SMBH,
followed by a less compact region till the BH influence radius r_i, and then
for r> r_i the known halo galaxy shows up with its astrophysical size. Three
representative families of galaxy plus central SMBH solutions are found and
analyzed:small, medium and large galaxies having SMBH masses of 10^5, 10^7 and
10^9 M_sun respectively. A minimum galaxy size and mass ~ 10^7 M_sun larger
than the one without SMBH is found. Small galaxies in the range 10^4 M_sun <
M_h < 10^7 M_sun cannot harbor central SMBHs. We find novel scaling M_BH - r_h
- M_h relations. The galaxy equation of state is derived: The pressure P(r)
takes huge values in the SMBH vecinity and then sharply decreases entering the
classical region following a local perfect gas behaviour.(Abridged)Comment: 31 pages, 14 figures, new materia
Equation of state, universal profiles, scaling and macroscopic quantum effects in Warm Dark Matter galaxies
The Thomas-Fermi approach to galaxy structure determines selfconsistently and
nonlinearly the gravitational potential of the fermionic WDM particles given
their quantum distribution function f(E). Galaxy magnitudes as the halo radius
r_h, mass M_h, velocity dispersion and phase space density are obtained. We
derive the general equation of state for galaxies (relation between the
pressure and the density), and provide an analytic expression. This clearly
exhibits two regimes: (i) Large diluted galaxies for M_h > 2.3 10^6 Msun
corresponding to temperatures T_0 > 0.017 K, described by the classical self
gravitating WDM Boltzman regime and (ii) Compact dwarf galaxies for 1.6 10^6
Msun > M_h>M_{h,min}=30000 (2keV/m)^{16/5} Msun, T_0<0.011 K described by the
quantum fermionic WDM regime. The T_0=0 degenerate quantum limit predicts the
most compact and smallest galaxy (minimal radius and mass M_{h,min}). All
magnitudes in the diluted regime exhibit square root of M_h scaling laws and
are universal functions of r/r_h when normalized to their values at the origin
or at r_h. We find that universality in galaxies (for M_h > 10^6 Msun) reflects
the WDM perfect gas behaviour. These theoretical results contrasted to robust
and independent sets of galaxy data remarkably reproduce the observations. For
the small galaxies, 10^6>M_h>M_{h,min} corresponding to effective temperatures
T_0 < 0.017 K, the equation of state is galaxy dependent and the profiles are
no more universal. These non-universal properties in small galaxies account to
the quantum physics of the WDM fermions in the compact regime. Our results are
independent of any WDM particle physics model, they only follow from the
gravitational interaction of the WDM particles and their fermionic quantum
nature.Comment: 21 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1309.229
Further remarks on isospin breaking in charmless semileptonic B decays
We consider the isospin breaking corrections to charmless semileptonic decays
of B mesons. Both, the recently measured branching ratios of exclusive decays
by the CLEO Collaboration and the end-point reion of the inclusive lepton
spectrum in form factor models, can be affected by these corrections. Isospin
corrections can affect the determination of |V_ub| from exclusive semileptonic
B decays at a level comparable to present statistical uncertainties.Comment: Latex, 7 pages, 1 .ps figure, to appear in Phys. Rev.
Statistical Mechanics of the Self-Gravitating Gas: Thermodynamic Limit, Unstabilities and Phase Diagrams
We show that the self-gravitating gas at thermal equilibrium has an infinite
volume limit in the three ensembles (GCE, CE, MCE) when (N, V) -> infty,
keeping N/V^{1/3} fixed, that is, with eta = G m^2 N/[ V^{1/3} T] fixed. We
develop MonteCarlo simulations, analytic mean field methods (MF) and low
density expansions. We compute the equation of state and find it to be locally
p(r) = T rho_V(r), that is a local ideal gas equation of state. The system is
in a gaseous phase for eta < eta_T = 1.51024...and collapses into a very dense
object for eta > eta_T in the CE with the pressure becoming large and negative.
The isothermal compressibility diverges at eta = eta_T. We compute the
fluctuations around mean field for the three ensembles. We show that the
particle distribution can be described by a Haussdorf dimension 1 < D < 3.Comment: 12 pages, Invited lecture at `Statistical Mechanics of Non-Extensive
Systems', Observatoire de Paris, October 2005, to be published in a Special
issue of `Les Comptes rendus de l'Acade'mie des sciences', Elsevie
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