22,391 research outputs found
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
Virtual QCD corrections to Higgs boson plus four parton processes
We report on the calculation of virtual processes contributing to the
production of a Higgs boson and two jets in hadron-hadron collisions. The
coupling of the Higgs boson to gluons, via a virtual loop of top quarks, is
treated using an effective theory, valid in the large top quark mass limit. The
calculation is performed by evaluating one-loop diagrams in the effective
theory. The primary method of calculation is a numerical evaluation of the
virtual amplitudes as a Laurent series in , where is the
dimensionality of space-time. For the cases and we confirm the numerical results by an explicit analytic
calculation.Comment: 21 pages, 2 figures. v2 modifies the text to agree with published
version and corrects typos in the analytical expressions for the four quark
amplitude
A cosmic equation of state for the inhomogeneous Universe: can a global far-from-equilibrium state explain Dark Energy?
A system of effective Einstein equations for spatially averaged scalar
variables of inhomogeneous cosmological models can be solved by providing a
`cosmic equation of state'. Recent efforts to explain Dark Energy focus on
`backreaction effects' of inhomogeneities on the effective evolution of
cosmological parameters in our Hubble volume, avoiding a cosmological constant
in the equation of state. In this Letter it is argued that, if kinematical
backreaction effects are indeed of the order of the averaged density (or larger
as needed for an accelerating domain of the Universe), then the state of our
regional Hubble volume would have to be in the vicinity of a
far-from-equilibrium state that balances kinematical backreaction and average
density. This property, if interpreted globally, is shared by a stationary
cosmos with effective equation of state . It
is concluded that a confirmed explanation of Dark Energy by kinematical
backreaction may imply a paradigmatic change of cosmology.Comment: 7 pages, matches published version in Class. Quant. Gra
Radiation measurements from polar and geosynchronous satellites
The following topics are discussed: (1) cloud effects in climate determination; (2) annual variation in the global heat balance of the earth; (3) the accuracy of precipitation estimates made from passive microwave measurements from satellites; (4) seasonal oceanic precipitation frequencies; (5) determination of mesoscale temperature and moisture fields over land from satellite radiance measurements; and (6) Nimbus 6 scanning microwave spectrometer data evaluation for surface wind and pressure components in tropical storms
Dynamics of Inflationary Universes with Positive Spatial Curvature
If the spatial curvature of the universe is positive, then the curvature term
will always dominate at early enough times in a slow-rolling inflationary
epoch. This enhances inflationary effects and hence puts limits on the possible
number of e-foldings that can have occurred, independently of what happened
before inflation began and in particular without regard for what may have
happened in the Planck era. We use a simple multi-stage model to examine this
limit as a function of the present density parameter and the epoch
when inflation ends.Comment: 9 Pages RevTex4. Revised and update
Impact of bosonic decays on the search for stau_2 and tau-sneutrino
We perform a detailed study of the decays of the heavier tau slepton (stau_2)
and tau-sneutrino (snu_tau) in the Minimal Supersymmetric Standard Model
(MSSM). We show that the decays into Higgs or gauge bosons, i.e. stau_2 ->
stau_1 + (h^0, H^0, A^0 or Z^0), stau_2 -> snu_tau + (H^- or W^-), and snu_tau
-> stau_1 + (H^+ or W^+), can be very important due to the sizable tau Yukawa
coupling and large mixing parameters of stau. Compared to the decays into
fermions, such as stau_2 -> tau + neutralino_i and stau_2 -> nu_tau +
chargino_j^-, these bosonic decay modes can have significantly different decay
distributions. This could have an important influence on the search for stau_2
and snu_tau and the determination of the MSSM parameters at future colliders.Comment: 12 pages, 3 figures, LaTeX2
Measures of fine tuning
Fine-tuning criteria are frequently used to place upper limits on the masses
of superpartners in supersymmetric extensions of the standard model. However,
commonly used prescriptions for quantifying naturalness have some important
shortcomings. Motivated by this, we propose new criteria for quantifying fine
tuning that can be used to place upper limits on superpartner masses with
greater fidelity. In addition, our analysis attempts to make explicit the
assumptions implicit in quantifications of naturalness. We apply our criteria
to the minimal supersymmetric extension of the standard model, and we find that
the scale of supersymmetry breaking can be larger than previous methods
indicate.Comment: 15 pages, LaTex, 5 figures uuencoded, gz-compressed file. Minor
revisions bring the archived manuscript into agreement with published versio
The faint-galaxy hosts of gamma-ray bursts
The observed redshifts and magnitudes of the host galaxies of gamma-ray
bursts (GRBs) are compared with the predictions of three basic GRB models, in
which the comoving rate density of GRBs is (1) proportional to the cosmic star
formation rate density, (2) proportional to the total integrated stellar
density and (3) constant. All three models make the assumption that at every
epoch the probability of a GRB occuring in a galaxy is proportional to that
galaxy's broad-band luminosity. No assumption is made that GRBs are standard
candles or even that their luminosity function is narrow. All three rate
density models are consistent with the observed GRB host galaxies to date,
although model (2) is slightly disfavored relative to the others. Models (1)
and (3) make very similar predictions for host galaxy magnitude and redshift
distributions; these models will be probably not be distinguished without
measurements of host-galaxy star-formation rates. The fraction of host galaxies
fainter than 28 mag may constrain the faint end of the galaxy luminosity
function at high redshift, or, if the fraction is observed to be low, may
suggest that the bursters are expelled from low-luminosity hosts. In all
models, the probability of finding a z<0.008 GRB among a sample of 11 GRBs is
less than 10^(-4), strongly suggesting that GRB 980425, if associated with
supernova 1998bw, represents a distinct class of GRBs.Comment: 7 pages, ApJ in press, revised to incorporate yet more new and
revised observational result
Is it possible to recover information from the black-hole radiation?
In the framework of communication theory, we analyse the gedanken experiment
in which beams of quanta bearing information are flashed towards a black hole.
We show that stimulated emission at the horizon provides a correlation between
incoming and outgoing radiations consisting of bosons. For fermions, the
mechanism responsible for the correlation is the Fermi exclusion principle.
Each one of these mechanisms is responsible for the a partial transfer of the
information originally coded in the incoming beam to the black--hole radiation.
We show that this process is very efficient whenever stimulated emission
overpowers spontaneous emission (bosons). Thus, black holes are not `ultimate
waste baskets of information'.Comment: 9 pages (2 figures available upon request), CERN-TH 6811/93, (LateX
file
- âŠ