857,260 research outputs found
The Unificatory Power of Scientific Realism
The no-miracles argument (Putnam, 1975) holds that science is successful because successful theories are (approximately) true. Frost-Arnold (2010) objects that this argument is unacceptable because it generates neither new predictions nor unifications. It is similar to the unacceptable explanation that opium puts people to sleep because it has a dormative virtue. I reply that on close examination, realism explains not only why some theories are successful but also why successful theories exist in current science. Therefore, it unifies the disparate phenomena
Top-Quark Pair Production Beyond Next-to-Leading Order
We report on recent calculations of the differential cross section for
top-quark pair production at hadron colliders. The results are differential
with respect to the top-pair invariant mass and to the partonic scattering
angle. In these calculations, which were carried out by employing
soft-collinear effective theory techniques, we resummed threshold logarithms up
to next-to-next-to-leading logarithmic order. Starting from the differential
cross section, it is possible to obtain theoretical predictions for the
invariant-mass distribution and the total cross section. We summarize here our
results for these observables, and we compare them with the results obtained
from different calculational methods.Comment: Talk presented at Loops and Legs in Quantum Field Theory 2010,
Woerlitz, Germany, April 25-30, 2010. 6 page
Genuine Tripartite Entanglement in a Spin-Star Network at Thermal Equilibrium
In a recent paper [M. Huber {\it et al}, Phys. Rev. Lett. {\bf 104}, 210501
(2010)] new criteria to find out the presence of multipartite entanglement have
been given. We exploit these tools in order to study thermal entanglement in a
spin-star network made of three peripheral spins interacting with a central
one. Genuine tripartite entanglement is found in a wide range of the relevant
parameters. A comparison between predictions based on the new criteria and on
the tripartite negativity is also given.Comment: 8 pages, 13 figure
Color fluctuation approximation for multiple interactions in leading twist theory of nuclear shadowing
The leading twist theory of nuclear shadowing predicts the shadowing
correction to nuclear parton distributions at small by connecting it to the
leading twist hard diffraction in electron-nucleon scattering. The
uncertainties of the predictions are related to the shadowing effects resulting
from the interaction of the hard probe with nucleons. We argue that
the pattern of hard diffraction observed at HERA allows one to reduce these
uncertainties. We develop a new approach to the treatment of these multiple
interactions, which is based on the concept of the color fluctuations and
accounts for the presence of both point-like and hadron-like configurations in
the virtual photon wave function. Using the developed framework, we update our
predictions for the leading twist nuclear shadowing in nuclear parton
distributions of heavy nuclei at small .Comment: 16 pages, 4 figures. Revised to address the Referee's comments.
Matches the published version, PLB 687 (2010) 167
Stability of non-time-reversible phonobreathers
Non-time reversible phonobreathers are non-linear waves that can transport
energy in coupled oscillator chains by means of a phase-torsion mechanism. In
this paper, the stability properties of these structures have been considered.
It has been performed an analytical study for low-coupling solutions based upon
the so called {\em multibreather stability theorem} previously developed by
some of the authors [Physica D {\bf 180} 235]. A numerical analysis confirms
the analytical predictions and gives a detailed picture of the existence and
stability properties for arbitrary frequency and coupling.Comment: J. Phys. A.:Math. and Theor. In Press (2010
Fluctuating and dissipative dynamics of dark solitons in quasi-condensates
The fluctuating and dissipative dynamics of matter-wave dark solitons within
harmonically trapped, partially condensed Bose gases is studied both
numerically and analytically. A study of the stochastic Gross-Pitaevskii
equation, which correctly accounts for density and phase fluctuations at finite
temperatures, reveals dark soliton decay times to be lognormally distributed at
each temperature, thereby characterizing the previously predicted long lived
soliton trajectories within each ensemble of numerical realizations (S.P.
Cockburn {\it et al.}, Phys. Rev. Lett. 104, 174101 (2010)). Expectation values
for the average soliton lifetimes extracted from these distributions are found
to agree well with both numerical and analytic predictions based upon the
dissipative Gross-Pitaevskii model (with the same {\it ab initio} damping).
Probing the regime for which , we find average
soliton lifetimes to scale with temperature as , in agreement
with predictions previously made for the low-temperature regime .
The model is also shown to capture the experimentally-relevant decrease in the
visibility of an oscillating soliton due to the presence of background
fluctuations.Comment: 17 pages, 14 figure
Interacting Preformed Cooper Pairs in Resonant Fermi Gases
We consider the normal phase of a strongly interacting Fermi gas, which can
have either an equal or an unequal number of atoms in its two accessible spin
states. Due to the unitarity-limited attractive interaction between particles
with different spin, noncondensed Cooper pairs are formed. The starting point
in treating preformed pairs is the Nozi\`{e}res-Schmitt-Rink (NSR) theory,
which approximates the pairs as being noninteracting. Here, we consider the
effects of the interactions between the Cooper pairs in a Wilsonian
renormalization-group scheme. Starting from the exact bosonic action for the
pairs, we calculate the Cooper-pair self-energy by combining the NSR formalism
with the Wilsonian approach. We compare our findings with the recent
experiments by Harikoshi {\it et al.} [Science {\bf 327}, 442 (2010)] and
Nascimb\`{e}ne {\it et al.} [Nature {\bf 463}, 1057 (2010)], and find very good
agreement. We also make predictions for the population-imbalanced case, that
can be tested in experiments.Comment: 10 pages, 6 figures, accepted version for PRA, discussion of the
imbalanced Fermi gas added, new figure and references adde
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