215 research outputs found
Interplanar binding in graphite studied with the Englert-Schwinger equation
A model of a graphite crystal is used which consists of a set of parallel slabs of positive charge immersed in an electron sea. The density of electrons in the region between slabs is calculated from the Englert-Schwinger equation. That equation improves Thomas-Fermi theory by including exchange and inhomogeneity corrections to the kinetic energy. The results are in semiquantitative agreement with empirical data and are slightly better than previous calculations of the interplanar binding of graphite
On the Price of Anarchy of Highly Congested Nonatomic Network Games
We consider nonatomic network games with one source and one destination. We
examine the asymptotic behavior of the price of anarchy as the inflow
increases. In accordance with some empirical observations, we show that, under
suitable conditions, the price of anarchy is asymptotic to one. We show with
some counterexamples that this is not always the case. The counterexamples
occur in very simple parallel graphs.Comment: 26 pages, 6 figure
Classical kinetic energy, quantum fluctuation terms and kinetic-energy functionals
We employ a recently formulated dequantization procedure to obtain an exact
expression for the kinetic energy which is applicable to all kinetic-energy
functionals. We express the kinetic energy of an N-electron system as the sum
of an N-electron classical kinetic energy and an N-electron purely quantum
kinetic energy arising from the quantum fluctuations that turn the classical
momentum into the quantum momentum. This leads to an interesting analogy with
Nelson's stochastic approach to quantum mechanics, which we use to conceptually
clarify the physical nature of part of the kinetic-energy functional in terms
of statistical fluctuations and in direct correspondence with Fisher
Information Theory. We show that the N-electron purely quantum kinetic energy
can be written as the sum of the (one-electron) Weizsacker term and an
(N-1)-electron kinetic correlation term. We further show that the Weizsacker
term results from local fluctuations while the kinetic correlation term results
from the nonlocal fluctuations. For one-electron orbitals (where kinetic
correlation is neglected) we obtain an exact (albeit impractical) expression
for the noninteracting kinetic energy as the sum of the classical kinetic
energy and the Weizsacker term. The classical kinetic energy is seen to be
explicitly dependent on the electron phase and this has implications for the
development of accurate orbital-free kinetic-energy functionals. Also, there is
a direct connection between the classical kinetic energy and the angular
momentum and, across a row of the periodic table, the classical kinetic energy
component of the noninteracting kinetic energy generally increases as Z
increases.Comment: 10 pages, 1 figure. To appear in Theor Chem Ac
Metric Fluctuation Corrections to Hawking Radiation
We study how fluctuations of the black hole geometry affect the properties of
Hawking radiation. Even though we treat the fluctuations classically, we
believe that the results so obtained indicate what might be the effects induced
by quantum fluctuations in a self consistent treatment. To characterize the
fluctuations, we use the model introduced by York in which they are described
by an advanced Vaidya metric with a fluctuating mass. Under the assumption of
spherical symmetry, we solve the equation of null outgoing rays. Then, by
neglecting the greybody factor, we calculate the late time corrections to the
s-wave contributions of the energy flux and the asymptotic spectrum. We find
three kind of modifications. Firstly, the energy flux fluctuates around its
average value with amplitudes and frequencies determined by those of the metric
fluctuations. Secondly, this average value receives two positive contributions
one of which can be reinterpreted as due to the `renormalisation' of the
surface gravity induced by the metric fluctuations. Finally, the asymptotic
spectrum is modified by the addition of terms containing thermal factors in
which the frequency of the metric fluctuations acts as a chemical potential.Comment: 27 pages, 2 figures, LaTeX. Revised versio
Gapped continuum Kaluza-Klein spectrum
We consider a warped ve-dimensional model with an ultraviolet (UV) brane
and, on top of the Standard Model isolated modes, continua of KK modes with different
mass gaps for all particles: gauge bosons, fermions, graviton, radion and Higgs boson. The
model can be considered as a modelization in ve dimensions of gapped unparticles. The
ve dimensional metric has a singularity, at a finite (infinite) value of the proper (conformal)
coordinate, which is admissible as it supports finite temperature in the form of a black
hole horizon. An infrared (IR) brane, with particular jumping conditions, is introduced
to trigger correct electroweak breaking. The gravitational metric is AdS5 near the UV
brane, to solve the hierarchy problem with a fundamental Planck scale, and linear, in
conformal coordinates, near the IR, as in the linear dilaton and ve-dimensional clockwork
models. The branes, and singularity, distances are fixed, Ă la Goldberger-Wise, by a bulk
scalar field with brane potentials explicitly breaking the conformal symmetry. The bosonic
continuum of KK modes with the smallest mass gap are those of gauge bosons, and so they
are the most likely produced at the LHC. Mass gaps of the continuum of KK fermions
do depend on their localization in the extra dimension. We have computed the spectral
functions, and arbitrary Green's functions, and shown how they can modify some Standard
Model processes.The work of EM is supported by the Spanish MINEICO under Grant FIS2017-85053-C2-1-P, by the Junta de AndalucĂa under Grant FQM-225, by
the ConsejerĂa de Conocimiento, InvestigaciĂłn y Universidad of the Junta de AndalucĂa and
European Regional Development Fund (ERDF) under Grant SOMM17/6105/UGR, and by
the Spanish Consolider Ingenio 2010 Programme CPAN under Grant CSD2007-00042. The
research of EM is also supported by the RamĂłn y Cajal Program of the Spanish MINEICO
under Grant RYC-2016-20678. The work of MQ is partly supported by Spanish MINEICO
(Grant FPA2017-88915-P), by the Catalan Government under Grant 2017SGR1069, and
by Severo Ochoa Excellence Program of MINEICO (Grant SEV-2016-0588)
Invisible Higgs and Dark Matter
We investigate the possibility that a massive weakly interacting fermion
simultaneously provides for a dominant component of the dark matter relic
density and an invisible decay width of the Higgs boson at the LHC. As a
concrete model realizing such dynamics we consider the minimal walking
technicolor, although our results apply more generally. Taking into account the
constraints from the electroweak precision measurements and current direct
searches for dark matter particles, we find that such scenario is heavily
constrained, and large portions of the parameter space are excluded.Comment: arXiv admin note: text overlap with arXiv:0912.229
Scaling Patterns for QCD Jets
Jet emission at hadron colliders follows simple scaling patterns. Based on
perturbative QCD we derive Poisson and staircase scaling for final state as
well as initial state radiation. Parton density effects enhance staircase
scaling at low multiplicities. We propose experimental tests of our theoretical
findings in Z+jets and QCD gap jets production based on minor additions to
current LHC analyses.Comment: 36 pages, 16 figure
Global Analysis of the Higgs Candidate with Mass ~ 125 GeV
We analyze the properties of the Higgs candidate with mass ~ 125 GeV
discovered by the CMS and ATLAS Collaborations, constraining the possible
deviations of its couplings from those of a Standard Model Higgs boson. The
CMS, ATLAS and Tevatron data are compatible with Standard Model couplings to
massive gauge bosons and fermions, and disfavour several types of composite
Higgs models unless their couplings resemble those in the Standard Model. We
show that the couplings of the Higgs candidate are consistent with a linear
dependence on particle masses, scaled by the electroweak scale ~ 246 GeV, the
power law and the mass scale both having uncertainties ~ 20%.Comment: 22 pages, 9 figures, v2 incorporates experimental data released
during July 2012 and corrected (and improved) treatment of mass dependence of
coupling
Measuring the Invisible Higgs Width at the 7 and 8 TeV LHC
The LHC is well on track toward the discovery or exclusion of a light
Standard Model (SM)-like Higgs boson. Such a Higgs has a very small SM width
and can easily have large branching fractions to physics beyond the SM, making
Higgs decays an excellent opportunity to observe new physics. Decays into
collider-invisible particles are particularly interesting as they are
theoretically well motivated and relatively clean experimentally. In this work
we estimate the potential of the 7 and 8 TeV LHC to observe an invisible Higgs
branching fraction. We analyze three channels that can be used to directly
study the invisible Higgs branching ratio at the 7 TeV LHC: an invisible Higgs
produced in association with (i) a hard jet; (ii) a leptonic Z; and (iii)
forward tagging jets. We find that the last channel, where the Higgs is
produced via weak boson fusion, is the most sensitive, allowing branching
fractions as small as 40% to be probed at 20 inverse fb for masses in the range
between 120 and 170 GeV, including in particular the interesting region around
125 GeV. We provide an estimate of the 8 TeV LHC sensitivity to an
invisibly-decaying Higgs produced via weak boson fusion and find that the reach
is comparable to but not better than the reach at the 7 TeV LHC. We further
estimate the discovery potential at the 8 TeV LHC for cases where the Higgs has
substantial branching fractions to both visible and invisible final states.Comment: 23 pages, 7 figures. v2: version published in JHEP. 8 TeV analysis
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Renormalized couplings and scaling correction amplitudes in the N-vector spin models on the sc and the bcc lattices
For the classical N-vector model, with arbitrary N, we have computed through
order \beta^{17} the high temperature expansions of the second field derivative
of the susceptibility \chi_4(N,\beta) on the simple cubic and on the body
centered cubic lattices. (The N-vector model is also known as the O(N)
symmetric classical spin Heisenberg model or, in quantum field theory, as the
lattice
O(N) nonlinear sigma model.) By analyzing the expansion of \chi_4(N,\beta) on
the two lattices, and by carefully allowing for the corrections to scaling, we
obtain updated estimates of the critical parameters and more accurate tests of
the hyperscaling relation d\nu(N) +\gamma(N) -2\Delta_4(N)=0 for a range of
values of the spin dimensionality N, including
N=0 [the self-avoiding walk model], N=1 [the Ising spin 1/2 model],
N=2 [the XY model], N=3 [the classical Heisenberg model]. Using the recently
extended series for the susceptibility and for the second correlation moment,
we also compute the dimensionless renormalized four point coupling constants
and some universal ratios of scaling correction amplitudes in fair agreement
with recent renormalization group estimates.Comment: 23 pages, latex, no figure
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