32,150,388 research outputs found
The evolution of the galaxy luminosity function in the rest frame blue band up to z=3.5
We present an estimate of the cosmological evolution of the field galaxy
luminosity function (LF) in the rest frame 4400 Angstrom B -band up to redshift
z=3.5. To this purpose, we use a composite sample of 1541 I--selected galaxies
selected down to I_(AB)=27.2 and 138 galaxies selected down to K_(AB)=25 from
ground-based and HST multicolor surveys, most notably the new deep JHK images
in the Hubble Deep Field South (HDF-S) taken with the ISAAC instrument at the
ESO-VLT telescope. About 21% of the sample has spectroscopic redshifts, and the
remaining fraction well calibrated photometric redshifts. The resulting blue LF
shows little density evolution at the faint end with respect to the local
values, while at the bright end (M_B(AB)<-20) a brightening increasing with
redshift is apparent with respect to the local LF. Hierarchical CDM models
overpredict the number of faint galaxies by about a factor 3 at z=1. At the
bright end the predicted LFs are in reasonable agreement only at low and
intermediate redshifts (z=1), but fail to reproduce the pronounced brightening
observed in the high redshift (z=2-3) LF. This brightening could mark the epoch
where a major star formation activity is present in the galaxy evolution.Comment: 14 pages, 2 figures, Astrophysical Journal Letters, in pres
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Mixed-mode oscillations in a multiple time scale phantom bursting system
In this work we study mixed mode oscillations in a model of secretion of GnRH
(Gonadotropin Releasing Hormone). The model is a phantom burster consisting of
two feedforward coupled FitzHugh-Nagumo systems, with three time scales. The
forcing system (Regulator) evolves on the slowest scale and acts by moving the
slow nullcline of the forced system (Secretor). There are three modes of
dynamics: pulsatility (transient relaxation oscillation), surge (quasi steady
state) and small oscillations related to the passage of the slow nullcline
through a fold point of the fast nullcline. We derive a variety of reductions,
taking advantage of the mentioned features of the system. We obtain two
results; one on the local dynamics near the fold in the parameter regime
corresponding to the presence of small oscillations and the other on the global
dynamics, more specifically on the existence of an attracting limit cycle. Our
local result is a rigorous characterization of small canards and sectors of
rotation in the case of folded node with an additional time scale, a feature
allowing for a clear geometric argument. The global result gives the existence
of an attracting unique limit cycle, which, in some parameter regimes, remains
attracting and unique even during passages through a canard explosion.Comment: 38 pages, 16 figure
Non-thermal Processes in Black-Hole-Jet Magnetospheres
The environs of supermassive black holes are among the universe's most
extreme phenomena. Understanding the physical processes occurring in the
vicinity of black holes may provide the key to answer a number of fundamental
astrophysical questions including the detectability of strong gravity effects,
the formation and propagation of relativistic jets, the origin of the highest
energy gamma-rays and cosmic-rays, and the nature and evolution of the central
engine in Active Galactic Nuclei (AGN). As a step towards this direction, this
paper reviews some of the progress achieved in the field based on observations
in the very high energy domain. It particularly focuses on non-thermal particle
acceleration and emission processes that may occur in the rotating
magnetospheres originating from accreting, supermassive black hole systems.
Topics covered include direct electric field acceleration in the black hole's
magnetosphere, ultra-high energy cosmic ray production, Blandford-Znajek
mechanism, centrifugal acceleration and magnetic reconnection, along with the
relevant efficiency constraints imposed by interactions with matter, radiation
and fields. By way of application, a detailed discussion of well-known sources
(Sgr A*; Cen A; M87; NGC1399) is presented.Comment: invited review for International Journal of Modern Physics D, 49
pages, 15 figures; minor typos corrected to match published versio
Black hole boundaries
Classical black holes and event horizons are highly non-local objects,
defined in relation to the causal past of future null infinity. Alternative,
quasilocal characterizations of black holes are often used in mathematical,
quantum, and numerical relativity. These include apparent, killing, trapping,
isolated, dynamical, and slowly evolving horizons. All of these are closely
associated with two-surfaces of zero outward null expansion. This paper reviews
the traditional definition of black holes and provides an overview of some of
the more recent work on alternative horizons.Comment: 27 pages, 8 figures, invited Einstein Centennial Review Article for
CJP, final version to appear in journal - glossary of terms added, typos
correcte
Relativity in Introductory Physics
A century after its formulation by Einstein, it is time to incorporate
special relativity early in the physics curriculum. The approach advocated here
employs a simple algebraic extension of vector formalism that generates
Minkowski spacetime, displays covariant symmetries, and enables calculations of
boosts and spatial rotations without matrices or tensors. The approach is part
of a comprehensive geometric algebra with applications in many areas of
physics, but only an intuitive subset is needed at the introductory level. The
approach and some of its extensions are given here and illustrated with
insights into the geometry of spacetime.Comment: 29 pages, 5 figures, several typos corrected, some discussion
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The twisted fourth moment of the Riemann zeta function
We compute the asymptotics of the fourth moment of the Riemann zeta function
times an arbitrary Dirichlet polynomial of length Comment: 28 pages. v2: added reference
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