19,592,891 research outputs found
Convergence of the Allen-Cahn equation with Neumann boundary conditions
We study a singular limit problem of the Allen-Cahn equation with Neumann
boundary conditions and general initial data of uniformly bounded energy. We
prove that the time-parametrized family of limit energy measures is Brakke's
mean curvature flow with a generalized right angle condition on the boundary.Comment: 26 pages, 1 figur
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
Relativistic kinetic theory of magnetoplasmas
Recently, an increasing interest in astrophysical as well as laboratory
plasmas has been manifested in reference to the existence of relativistic
flows, related in turn to the production of intense electric fields in
magnetized systems. Such phenomena require their description in the framework
of a consistent relativistic kinetic theory, rather than on relativistic MHD
equations, subject to specific closure conditions. The purpose of this work is
to apply the relativistic single-particle guiding-center theory developed by
Beklemishev and Tessarotto, including the nonlinear treatment of
small-wavelength EM perturbations which may naturally arise in such systems. As
a result, a closed set of relativistic gyrokinetic equations, consisting of the
collisionless relativistic kinetic equation, expressed in hybrid gyrokinetic
variables, and the averaged Maxwell's equations, is derived for an arbitrary
four-dimensional coordinate system.Comment: 6 pages, 1 figure. Contributed to the Proceedings of the 24th
International Symposium on Rarefied Gas Dynamics, July 10-16, 2004 Porto
Giardino Monopoli (Bari), Ital
Lyman Alpha Emitter Evolution in the Reionization Epoch
Combining cosmological SPH simulations with a previously developed Lyman
Alpha production/transmission model and the Early Reionization Model (ERM,
reionization ends at redshift z~7), we obtain Lyman Alpha and UV Luminosity
Functions (LFs) for Lyman Alpha Emitters (LAEs) for redshifts between 5.7 and
7.6. Matching model results to observations at z~5.7 requires escape fractions
of Lyman Alpha, f_alpha=0.3, and UV (non-ionizing) continuum photons, f_c=0.22,
corresponding to a color excess, E(B-V)=0.15. We find that (i) f_c increases
towards higher redshifts, due the decreasing mean dust content of galaxies,
(ii) the evolution of f_alpha/f_c hints at the dust content of the ISM becoming
progressively inhomogeneous/clumped with decreasing redshift. The clustering
photoionization boost is important during the initial reionization phases but
has little effect on the Lyman Alpha LF for a highly ionized IGM. Halo
(stellar) masses are in the range 10.0 < \log M_h < 11.8 (8.1 < \log M_* <
10.4) with M_h \propto M_*^{0.64}. The star formation rates are between 3-120
solar masses per year, mass-weighted mean ages are greater than 20 Myr at all
redshifts, while the mean stellar metallicity increases from Z=0.12 to 0.22
solar metallicity from z~7.6 to z~5.7; both age and metallicity positively
correlate with stellar mass. The brightest LAEs are all characterized by large
star formation rates and intermediate ages (~200 Myr), while objects in the
faint end of the Lyman Alpha LF show large age and star formation rate spreads.
With no more free parameters, the Spectral Energy Distributions of three LAE at
z~5.7 observed by Lai et al. (2007) are well reproduced by an intermediate age
(182-220 Myr) stellar population and the above E(B-V) value.Comment: 13 pages, 9 figures, accepted to MNRA
Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data
collected with the CDF II detector at the Tevatron corresponding to an
integrated luminosity of 9.45 fb-1. In events consistent with the decay of the
Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a
neutrino, we set 95% credibility level upper limits on the WH production cross
section times the H->bb branching ratio as a function of Higgs boson mass. At a
Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times
the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by
PRL
Large-time Behavior of Solutions to the Inflow Problem of Full Compressible Navier-Stokes Equations
Large-time behavior of solutions to the inflow problem of full compressible
Navier-Stokes equations is investigated on the half line .
The wave structure which contains four waves: the transonic(or degenerate)
boundary layer solution, 1-rarefaction wave, viscous 2-contact wave and
3-rarefaction wave to the inflow problem is described and the asymptotic
stability of the superposition of the above four wave patterns to the inflow
problem of full compressible Navier-Stokes equations is proven under some
smallness conditions. The proof is given by the elementary energy analysis
based on the underlying wave structure. The main points in the proof are the
degeneracies of the transonic boundary layer solution and the wave interactions
in the superposition wave.Comment: 27 page
Life in a warm deep sea: routine activity and burst swimming performance of the shrimp Acanthephyra eximia in the abyssal Mediterranean
Measurements of routine swimming speed, "tail-flip'' escape responses, and oxygen consumptions were made of the deep-sea shrimp Acanthephyra eximia using autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13 - 14.5 degrees C. Routine swimming speeds at 4,200 m averaged 0.18 m s(-1) or 3.09 body lengths s(-1), approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s(-2) or 630.6 body lengths s(-2) were recorded, with animals reaching speeds of 1.61 m s(-1) or 34.8 body lengths s(-2). When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such as A. eximia despite a maximum muscle mass specific power output of 90.0 W kg(-1). A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure
Search for the standard model Higgs boson decaying to a bb pair in events with two oppositely-charged leptons using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a Z boson in data collected with the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45/fb. In events
consistent with the decay of the Higgs boson to a bottom-quark pair and the Z
boson to electron or muon pairs, we set 95% credibility level upper limits on
the ZH production cross section times the H -> bb branching ratio as a function
of Higgs boson mass. At a Higgs boson mass of 125 GeV/c^2 we observe (expect) a
limit of 7.1 (3.9) times the standard model value.Comment: To be submitted to Phys. Rev. Let
Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption
Neutrinos interact only very weakly, so they are extremely penetrating.
However, the theoretical neutrino-nucleon interaction cross section rises with
energy such that, at energies above 40 TeV, neutrinos are expected to be
absorbed as they pass through the Earth. Experimentally, the cross section has
been measured only at the relatively low energies (below 400 GeV) available at
neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here
we report the first measurement of neutrino absorption in the Earth, using a
sample of 10,784 energetic upward-going neutrino-induced muons observed with
the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting
long paths through the Earth is attenuated compared to a reference sample that
follows shorter trajectories through the Earth. Using a fit to the
two-dimensional distribution of muon energy and zenith angle, we determine the
cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an
order of magnitude higher in energy than previous measurements. The measured
cross section is (stat.) (syst.)
times the prediction of the Standard Model \cite{CooperSarkar:2011pa},
consistent with the expectation for charged and neutral current interactions.
We do not observe a dramatic increase in the cross section, expected in some
speculative models, including those invoking new compact dimensions
\cite{AlvarezMuniz:2002ga} or the production of leptoquarks
\cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445
- …