3,422 research outputs found
High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets
The dynamics of vibrational wave packets in triplet states of rubidium dimers
(Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe
photoionization spectroscopy. Due to fast desorption of the excited Rb2
molecules off the droplets and due to their low internal temperature, wave
packet oscillations can be followed up to very long pump-probe delay times
>1.5ns. In the first excited triplet state (1)^3\Sigma_g^+, full and fractional
revivals are observed with high contrast. Fourier analysis provides
high-resolution vibrational spectra which are in excellent agreement with ab
initio calculations
Cosmological gravitino problem confronts electroweak physics
A generic feature of gauge-mediated supersymmetry breaking models is that the
gravitino is the lightest supersymmetric particle (LSP). In order not to
overclose the universe, the gravitino LSP should be light enough (~ 1 keV), or
appropriately heavy (~ 1 GeV). We study further constraints on the mass of the
gravitino imposed by electroweak experiments, i.e., muon g-2 measurements,
electroweak precision measurements, and direct searches for supersymmetric
particles at LEP2. We find that the heavy gravitino is strongly disfavored from
the lower mass bound on the next-to-LSP. The sufficiently light gravitino, on
the other hand, has rather sizable allowed regions in the model parameter
space.Comment: 11 pages, 8 figures, version to appear in PR
The B_s and D_s decay constants in 3 flavor lattice QCD
Capitalizing on recent advances in lattice QCD, we present a calculation of
the leptonic decay constants f_{B_s} and f_{D_s} that includes effects of one
strange sea quark and two light sea quarks. The discretization errors of
improved staggered fermion actions are small enough to simulate with 3
dynamical flavors on lattices with spacings around 0.1 fm using present
computer resources. By shedding the quenched approximation and the associated
lattice scale ambiguity, lattice QCD greatly increases its predictive power.
NRQCD is used to simulate heavy quarks with masses between 1.5 m_c and m_b. We
arrive at the following results: f_{B_s} = 260 \pm 7 \pm 26 \pm 8 \pm 5 MeV and
f_{D_s} = 290 \pm 20 \pm 29 \pm 29 \pm 6 MeV. The first quoted error is the
statistical uncertainty, and the rest estimate the sizes of higher order terms
neglected in this calculation. All of these uncertainties are systematically
improvable by including another order in the weak coupling expansion, the
nonrelativistic expansion, or the Symanzik improvement program.Comment: 4 page
Universal Extra Dimensions and the Higgs Boson Mass
We study the combined constraints on the compactification scale 1/R and the
Higgs mass m_H in the standard model with one or two universal extra
dimensions. Focusing on precision measurements and employing the
Peskin-Takeuchi S and T parameters, we analyze the allowed region in the (m_H,
1/R) parameter space consistent with current experiments. For this purpose, we
calculate complete one-loop KK mode contributions to S, T, and U, and also
estimate the contributions from physics above the cutoff of the
higher-dimensional standard model. A compactification scale 1/R as low as 250
GeV and significantly extended regions of m_H are found to be consistent with
current precision data.Comment: 21 pages, Latex, 6 eps figures, an error in calculations was
corrected and results of analysis changed accordingly, references adde
Measuring the Higgs boson's parity using tau --> rho nu
We present a very promising method for a measurement of the Higgs boson
parity using the H/A -> tau^+ tau^- --> rho^+ nu rho^- nu --> pi^+ pi^0 nu pi^-
pi^0 nu decay chain. The method is both model independent and independent of
the Higgs production mechanism. Angular distributions of the tau decay products
which are sensitive to the Higgs boson parity are defined and are found to be
measurable using typical properties of a future detector for an e^+ e^- linear
collider. The prospects for the measurement of the parity of a Higgs boson with
a mass of 120 GeV are quantified for the case of e^+ e^- collisons of 500 GeV
center of mass energy with an integrated luminosity of 500 fb^-1. The Standard
Model Higgsstrahlung production process is used as an example.Comment: 10 pages, 4 figures, LaTeX, version of Phys. Lett.
Searching for a light Fermiophobic Higgs Boson at the Tevatron
We propose new production mechanisms for light fermiophobic Higgs bosons
() with suppressed couplings to vector bosons () at the Fermilab
Tevatron. These mechanisms (e.g. ) are complementary to the
conventional process , which suffers from a strong suppression of
in realistic models with a . The new mechanisms extend the
coverage at the Tevatron Run II to the larger region, and offer the
possibility of observing new event topologies with up to 4 photons.Comment: 15 pages, including 5 eps-figure
QCD Corrections to Vector-Boson Fusion Processes in Warped Higgsless Models
We discuss the signatures of a representative Higgsless model with ideal
fermion delocalization in vector-boson fusion processes, focusing on the gold-
and silver-plated decay modes of the gauge bosons at the CERN-Large Hadron
Collider. For this purpose, we have developed a fully-flexible parton-level
Monte-Carlo program, which allows for the calculation of cross sections and
kinematic distributions within experimentally feasible selection cuts at
NLO-QCD accuracy. We find that Kaluza-Klein resonances give rise to very
distinctive distributions of the decay leptons. Similar to the Standard Model
case, within the Higgsless scenario the perturbative treatment of the
vector-boson scattering processes is under excellent control.Comment: 22 pages, 20 figure
Resummation of heavy jet mass and comparison to LEP data
The heavy jet mass distribution in e+e- collisions is computed to
next-to-next-to-next-to leading logarithmic (NNNLL) and next-to-next-to leading
fixed order accuracy (NNLO). The singular terms predicted from the resummed
distribution are confirmed by the fixed order distributions allowing a precise
extraction of the unknown soft function coefficients. A number of quantitative
and qualitative comparisons of heavy jet mass and the related thrust
distribution are made. From fitting to ALEPH data, a value of alpha_s is
extracted, alpha_s(m_Z)=0.1220 +/- 0.0031, which is larger than, but not in
conflict with, the corresponding value for thrust. A weighted average of the
two produces alpha_s(m_Z) = 0.1193 +/- 0.0027, consistent with the world
average. A study of the non-perturbative corrections shows that the flat
direction observed for thrust between alpha_s and a simple non-perturbative
shape parameter is not lifted in combining with heavy jet mass. The Monte Carlo
treatment of hadronization gives qualitatively different results for thrust and
heavy jet mass, and we conclude that it cannot be trusted to add power
corrections to the event shape distributions at this accuracy. Whether a more
sophisticated effective field theory approach to power corrections can
reconcile the thrust and heavy jet mass distributions remains an open question.Comment: 33 pages, 14 figures. v2 added effect of lower numerical cutoff with
improved extraction of the soft function constants; power correction
discussion clarified. v3 small typos correcte
Supersymmetry and the Cosmic Ray Positron Excess
We explore several supersymmetric alternatives to explain predictions for the
cosmic ray positron excess. Light sneutrino or neutralino LSP's, and a
fine-tuned model designed to provide a delta-function input, can give adequate
statistical descriptions of the reported HEAT data if non-thermal production of
the relic cold dark matter density dominates and/or if ``boost factors''(that
could originate in uncertainties from propagation or local density
fluctuations) to increase the size of the signal are included. All the
descriptions can be tested at the Tevatron or LHC, and some in other WIMP
detecting experiments.Comment: 15 pages, 3 figure
The deal.II Library, Version 8.3
deal.II version 8.3 was released August 1, 2015. This paper provides an overview of the new features of this release and serves as a citable reference for the deal.II software library version 8.3. deal.II is an object-oriented finite element library used around the world in the development of finite element solvers. It is available for free under the GNU Lesser General Public License (LGPL) from the deal.II homepage at http://www.dealii.org/
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