4,781 research outputs found
Thermodynamics of the BCS-BEC crossover
We present a self-consistent theory for the thermodynamics of the BCS-BEC
crossover in the normal and superfluid phase which is both conserving and
gapless. It is based on the variational many-body formalism developed by
Luttinger and Ward and by DeDominicis and Martin. Truncating the exact
functional for the entropy to that obtained within a ladder approximation, the
resulting self-consistent integral equations for the normal and anomalous Green
functions are solved numerically for arbitrary coupling. The critical
temperature, the equation of state and the entropy are determined as a function
of the dimensionless parameter , which controls the crossover from the
BCS-regime of extended pairs to the BEC-regime of tightly bound molecules. The
tightly bound pairs turn out to be described by a Popov-type approximation for
a dilute, repulsive Bose gas. Even though our approximation does not capture
the critical behaviour near the continuous superfluid transition, our results
provide a consistent picture for the complete crossover thermodynamics which
compare well with recent numerical and field-theoretic approaches at the
unitarity point.Comment: published versio
An Extension of a result of Csiszar
We extend the results of Csiszar (Z. Wahr. 5(1966) 279-295) to a topological semigroup S. Let μ be a measure defined on S. We consider the value of α=supKcompactlimn→∞supx∈Sμn(Kx−1). First. we show that the value of α is either zero or one. If α=1, we show that there exists a sequence of elements {an} In S such that μn∗δan converges vaguely to a probability measure where δ denotes point mass. In particular, we apply the results to inverse and matrix semigroups
A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery
The standard model of particle physics1-4 describes the known fundamental particles and forces that make up our Universe, with the exception of gravity. One of the central features of the standard model is a field that permeates all of space and interacts with fundamental particles5-9. The quantum excitation of this field, known as the Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the standard model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN10,11. Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, enabling much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and W and Z bosons-the carriers of the strong, electromagnetic and weak forces-are studied in detail. Interactions with three third-generation matter particles (bottom (b) and top (t) quarks, and tau leptons (τ)) are well measured and indications of interactions with a second-generation particle (muons, μ) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the standard model
Automated Synthesis of Tableau Calculi
This paper presents a method for synthesising sound and complete tableau
calculi. Given a specification of the formal semantics of a logic, the method
generates a set of tableau inference rules that can then be used to reason
within the logic. The method guarantees that the generated rules form a
calculus which is sound and constructively complete. If the logic can be shown
to admit finite filtration with respect to a well-defined first-order semantics
then adding a general blocking mechanism provides a terminating tableau
calculus. The process of generating tableau rules can be completely automated
and produces, together with the blocking mechanism, an automated procedure for
generating tableau decision procedures. For illustration we show the
workability of the approach for a description logic with transitive roles and
propositional intuitionistic logic.Comment: 32 page
Scales of Fermion Mass Generation and Electroweak Symmetry Breaking
The scale of mass generation for fermions (including neutrinos) and the scale
for electroweak symmetry breaking (EWSB) can be bounded from above by the
unitarity of scattering involving longitudinal weak gauge bosons or their
corresponding would-be Goldstone bosons. Including the exact n-body phase space
we analyze the 2 --> n () processes for the fermion-(anti)fermion
scattering into multiple gauge boson final states. Contrary to naive energy
power counting, we demonstrate that as becomes large, the competition
between an increasing energy factor and a phase-space suppression leads to a
{\it strong new upper bound} on the scale of fermion mass generation at a
finite value , which is {\it independent of the EWSB scale,} . For quarks, leptons and Majorana neutrinos, the
strongest 2 --> n limits range from about 3TeV to 130-170TeV (with ), depending on the measured fermion masses. Strikingly, given
the tiny neutrino masses as constrained by the neutrino oscillations,
neutrinoless double-beta decays and astrophysical observations, the unitarity
violation of scattering actually occurs at a scale no
higher than ~170 TeV. Implications for various mechanisms of neutrino mass
generation are analyzed. On the other hand, for the 2 --> n pure
Goldstone-boson scattering, we find that the decreasing phase space factor
always dominates over the growing overall energy factor when becomes large,
so that the best unitarity bound on the scale of EWSB remains at n=2.Comment: 67pp, to match PRD (minor typos fixed
Evidence for t\bar{t}\gamma Production and Measurement of \sigma_t\bar{t}\gamma / \sigma_t\bar{t}
Using data corresponding to 6.0/fb of ppbar collisions at sqrt(s) = 1.96 TeV
collected by the CDF II detector, we present a cross section measurement of
top-quark pair production with an additional radiated photon. The events are
selected by looking for a lepton, a photon, significant transverse momentum
imbalance, large total transverse energy, and three or more jets, with at least
one identified as containing a b quark. The ttbar+photon sample requires the
photon to have 10 GeV or more of transverse energy, and to be in the central
region. Using an event selection optimized for the ttbar+photon candidate
sample we measure the production cross section of, and the ratio of cross
sections of the two samples. Control samples in the dilepton+photon and
lepton+photon+\met, channels are constructed to aid in decay product
identification and background measurements. We observe 30 ttbar+photon
candidate events compared to the standard model expectation of 26.9 +/- 3.4
events. We measure the ttbar+photon cross section to be 0.18+0.08 pb, and the
ratio of the cross section of ttbar+photon to ttbar to be 0.024 +/- 0.009.
Assuming no ttbar+photon production, we observe a probability of 0.0015 of the
background events alone producing 30 events or more, corresponding to 3.0
standard deviations.Comment: 9 pages, 3 figure
Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV
We search for the standard model Higgs boson produced in association with an
electroweak vector boson in events with no identified charged leptons, large
imbalance in transverse momentum, and two jets where at least one contains a
secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1
integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV
recorded by the CDF II experiment at the Tevatron. We find 268 (16) single
(double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are
expected from standard model background processes. We place 95% confidence
level upper limits on the Higgs boson production cross section for several
Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115
GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model
prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
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