512 research outputs found
QCD-Factorization of inclusive B decays and |Vub|
Recent progress in the theoretical description of inclusive B to X_u l nu
decays in the shape-function region is reported. Finite moments of the shape
function are related to HQET parameters. Event fractions for several
experimental cuts are presented, with a particular emphasis on the hadronic
variable P+. The aim of this talk is to introduce the P+ spectrum, to compare
it to the hadronic invariant mass spectrum and the charged-lepton energy
spectrum, and to study the prospect of evaluating |Vub| in the presence of a
large background from B to X_c decays.Comment: 8 pages, 7 figures, uses espcrc2.sty (included). Talk presented at
the Sixth International Conference on Hyperons, Charm and Beauty Hadrons,
IIT, Chicago, June 27--July 3 200
A two-loop relation between inclusive radiative and semileptonic B-decay spectra
A shape-function independent relation is derived between the partial
B->X_u+l+nu decay rate with a cut on P_+=E_X-P_X<Delta and a weighted integral
over the normalized B->X_s+gamma photon-energy spectrum. The leading-power
contribution to the weight function is calculated at next-to-next-to-leading
order in renormalization-group improved perturbation theory, including exact
two-loop matching corrections at the scale mu_i^2 ~ m_b*Lambda_{QCD}. The
overall normalization of the weight function is obtained up to yet unknown
corrections of order [alpha_s(m_b)]^2. Power corrections from phase-space
factors are included exactly, while the remaining subleading contributions are
included at first order in 1/m_b. At this level unavoidable hadronic
uncertainties enter, which are estimated in a conservative way. The combined
theoretical accuracy in the extraction of |V_{ub}| is at the level of 5% if a
value of Delta near the charm threshold can be achieved experimentally.Comment: 22 pages, 4 figures; few comments and one reference added; version to
appear in JHE
Precision Determination of
The last two years have seen an impressive improvement in the determination
of , especially from inclusive decays. The error on
measured with inclusive decays was reduced from 18% (PDG 2004) to 8% (PDG
2006). This progress is a result of combined experimental and theoretical
efforts. In this talk, the theoretical framework (BLNP) that enabled such
progress is reviewed, as well as other approaches to an inclusive determination
of (DGE, etc.). The prospects of improving are
discussed, addressing issues of weak annihilation, implications of leptonic B
decays, and determination of with exclusive decays.Comment: Invited talk at International Conference on B-Physics at Hadron
Machines (Beauty 2006), Oxford, England, 25-29 Sep 200
Constraints on Assembly Bias from Galaxy Clustering
We constrain the newly-introduced decorated Halo Occupation Distribution
(HOD) model using SDSS DR7 measurements of projected galaxy clustering or
r-band luminosity threshold samples. The decorated HOD is a model for the
galaxy-halo connection that augments the HOD by allowing for the possibility of
galaxy assembly bias: galaxy luminosity may be correlated with dark matter halo
properties besides mass, Mvir. We demonstrate that it is not possible to rule
out galaxy assembly bias using DR7 measurements of galaxy clustering alone.
Moreover, galaxy samples with Mr < -20 and Mr < -20.5 favor strong central
galaxy assembly bias. These samples prefer scenarios in which
high-concentration are more likely to host a central galaxy relative to
low-concentration halos of the same mass. We exclude zero assembly bias with
high significance for these samples. Satellite galaxy assembly bias is
significant for the faintest sample, Mr < -19. We find no evidence for assembly
bias in the Mr < -21 sample. Assembly bias should be accounted for in galaxy
clustering analyses or attempts to exploit galaxy clustering to constrain
cosmology. In addition to presenting the first constraints on HOD models that
accommodate assembly bias, our analysis includes several improvements over
previous analyses of these data. Therefore, our inferences supersede
previously-published results even in the case of a standard HOD analysis.Comment: 15 pages, 8 figures. To be submitted to MNRAS. Comments Welcome.
Python scripts to perform this analysis and MCMC chains will all be made
publicly availabl
Maturing Satellite Kinematics into a Competitive Probe of the Galaxy-Halo Connection
The kinematics of satellite galaxies moving in a dark matter halo are a
direct probe of the underlying gravitational potential. Thus, the phase-space
distributions of satellites represent a powerful tool to determine the
galaxy-halo connection from observations. By stacking the signal of a large
number of satellite galaxies this potential can be unlocked even for haloes
hosting a few satellites on average. In this work, we test the impact of
various modelling assumptions on constraints derived from analysing satellite
phase-space distributions in the non-linear, 1-halo regime. We discuss their
potential to explain the discrepancy between average halo masses derived from
satellite kinematics and gravitational lensing previously reported.
Furthermore, we develop an updated, more robust analysis to extract constraints
on the galaxy-halo relation from satellite properties in spectroscopic galaxy
surveys such as the SDSS. We test the accuracy of this approach using a large
number of realistic mock catalogues. Furthermore, we find that constraints
derived from such an analysis are complementary and competitive with respect to
the commonly used galaxy clustering and galaxy-galaxy lensing observables.Comment: 24 pages, 15 figures; resubmitted to MNRAS after first referee repor
Updated Results on the Galaxy-Halo Connection from Satellite Kinematics in SDSS
We present new results on the relationship between central galaxies and dark
matter haloes inferred from observations of satellite kinematics in the Sloan
Digital Sky Survey (SDSS) DR7. We employ an updated analysis framework that
includes detailed mock catalogues to model observational effects in SDSS. Our
results constrain the colour-dependent conditional luminosity function (CLF) of
dark matter haloes, as well as the radial profile of satellite galaxies.
Confirming previous results, we find that red central galaxies live in more
massive haloes than blue galaxies at fixed luminosity. Additionally, our
results suggest that satellite galaxies have a radial profile less centrally
concentrated than dark matter but not as cored as resolved subhaloes in dark
matter-only simulations. Compared to previous works using satellite kinematics
by More et al., we find much more competitive constraints on the galaxy-halo
connection, on par with those derived from a combination of galaxy clustering
and galaxy-galaxy lensing. We compare our results on the galaxy-halo connection
to other studies using galaxy clustering and group catalogues, showing very
good agreement between these different techniques. We discuss future
applications of satellite kinematics in the context of constraining cosmology
and the relationship between galaxies and dark matter haloes.Comment: 18 pages, 10 figures, submitted to MNRAS, comments welcom
Proposal for a Precision Measurement of |Vub|
A new method for a precision measurement of the CKM matrix element |Vub| is
discussed, which combines good theoretical control with high efficiency and a
powerful discrimination against charm background. The resulting combined
theoretical uncertainty on |Vub| is estimated to be 10%.Comment: 4 pages, 2 figures, RevTe
Brightest galaxies as halo centre tracers in SDSS DR7
Determining the positions of halo centres in large-scale structure surveys is
crucial for many cosmological studies. A common assumption is that halo centres
correspond to the location of their brightest member galaxies. In this paper,
we study the dynamics of brightest galaxies with respect to other halo members
in the Sloan Digital Sky Survey DR7. Specifically, we look at the line-of-sight
velocity and spatial offsets between brightest galaxies and their neighbours.
We compare those to detailed mock catalogues, constructed from high-resolution,
dark-matter-only -body simulations, in which it is assumed that satellite
galaxies trace dark matter subhaloes. This allows us to place constraints on
the fraction of haloes in which the brightest galaxy is not the
central. Compared to previous studies we explicitly take into account the
unrelaxed state of the host haloes, velocity offsets of halo cores and
correlations between and the satellite occupation. We find that
strongly decreases with the luminosity of the brightest galaxy
and increases with the mass of the host halo. Overall, in the halo mass range
we find , in good
agreement with a previous study by Skibba et al. We discuss the implications of
these findings for studies inferring the galaxy--halo connection from satellite
kinematics, models of the conditional luminosity function and galaxy formation
in general.Comment: 24 pages, 15 figures. Accepted for publication in MNRA
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