1,148 research outputs found
Condensates of Strongly-interacting Atoms and Dynamically Generated Dimers
In a system of atoms with large positive scattering length, weakly-bound
diatomic molecules (dimers) are generated dynamically by the strong
interactions between the atoms. If the atoms are modeled by a quantum field
theory with an atom field only, condensates of dimers cannot be described by
the mean-field approximation because there is no field associated with the
dimers. We develop a method for describing dimer condensates in such a model
based on the one-particle-irreducible (1PI) effective action. We construct an
equivalent 1PI effective action that depends not only on the classical atom
field but also on a classical dimer field. The method is illustrated by
applying it to the many-body behavior of bosonic atoms with large scattering
length at zero temperature using an approximation in which the 2-atom amplitude
is treated exactly but irreducible -atom amplitudes for are
neglected. The two 1PI effective actions give identical results for the atom
superfluid phase, but the one with a classical dimer field is much more
convenient for describing the dimer superfluid phase. The results are also
compared with previous work on the Bose gas near a Feshbach resonance.Comment: 10 figure
Effects of hadronic loops on the direct CP violation of
It is well known that the final state interaction plays an important role in
the decays of -meson. The contribution of the final state interaction which
is supposed to be long-distance effects, to the concerned processes can
interfere with that of the short-distance effects produced via the tree and/or
loop diagrams at quark-gluon level. The interference may provide a source for
the direct CP violation in the process . We find that a typical value of when the
final state interaction effect is taken into account can be about -22% which is
different from that without the final state interaction effect. Therefore, when
we extract information on CP violation from the data which will be available at
LHCb and the new experiments in -factories, the contribution from the final
state interaction must be included. This study may be crucial for searching new
physics in the future.Comment: 15 pages, 3 figures, 2 tables. More discussion adde
An Effective Field Theory Look at Deep Inelastic Scattering
This talk discusses the effective field theory view of deep inelastic
scattering. In such an approach, the standard factorization formula of a hard
coefficient multiplied by a parton distribution function arises from matching
of QCD onto an effective field theory. The DGLAP equations can then be viewed
as the standard renormalization group equations that determines the cut-off
dependence of the non-local operator whose forward matrix element is the parton
distribution function. As an example, the non-singlet quark splitting functions
is derived directly from the renormalization properties of the non-local
operator itself. This approach, although discussed in the literature, does not
appear to be well known to the larger high energy community. In this talk we
give a pedagogical introduction to this subject.Comment: 11 pages, 1 figure, To appear in Modern Physics Letters
QED Electrical Conductivity using the 2PI Effective Action
In this article we calculate the electrical conductivity in QED using the 2PI
effective action. We use a modified version of the usual 2PI effective action
which is defined with respect to self-consistent solutions of the 2-point
functions. We show that the green functions obtained from this modified
effective action satisfy ward identities and that the conductivity obtained
from the kubo relation is gauge invariant. We work to 3-loop order in the
modified 2PI effective action and show explicitly that the resulting expression
for the conductivity contains the square of the amplitude that corresponds to
all binary collision and production processes.Comment: 24 pages, 21 figure
Transverse-momentum distributions in a diquark spectator model
All the leading-twist parton distribution functions are calculated in a
spectator model of the nucleon, using scalar and axial-vector diquarks. Single
gluon rescattering is used to generate T-odd distribution functions. Different
choices for the diquark polarization states are considered, as well as a few
options for the form factor at the nucleon-quark-diquark vertex. The results
are listed in analytic form and interpreted in terms of light-cone wave
functions. The model parameters are fixed by reproducing the phenomenological
parametrization of unpolarized and helicity parton distributions at the lowest
available scale. Predictions for the other parton densities are given and,
whenever possible, compared with available phenomenological parametrizations.Comment: 42 pages, 13 figures in .eps format. RevTeX style. Minor typos
corrected, added one referenc
Induced current in the presence of magnetic flux tube of small radius
The induced current density, corresponding to the massless Dirac equation in
(2+1) dimensions in a magnetic flux tube of small radius is considered. This
problem is important for graphene. In the case, when an electron can not
penetrate the region of nonzero magnetic field, this current is the odd
periodical function of the magnetic flux. If the region inside the magnetic
tube is not forbidden for penetration of electron, the induced current is not a
periodical function of the magnetic flux. However in the limit , where
is the radius of magnetic flux tube, this function has the universal form
which is independent of the magnetic field distribution inside the magnetic
tube at fixed value of the magnetic flux.Comment: 5 pages, 1 figur
Cosmology With Many Light Scalar Fields: Stochastic Inflation and Loop Corrections
We explore the consequences of the existence of a very large number of light
scalar degrees of freedom in the early universe. We distinguish between
participator and spectator fields. The former have a small mass, and can
contribute to the inflationary dynamics; the latter are either strictly
massless or have a negligible VEV. In N-flation and generic assisted inflation
scenarios, inflation is a co-operative phenomenon driven by N participator
fields, none of which could drive inflation on their own. We review upper
bounds on N, as a function of the inflationary Hubble scale H. We then consider
stochastic and eternal inflation in models with N participator fields showing
that individual fields may evolve stochastically while the whole ensemble
behaves deterministically, and that a wide range of eternal inflationary
scenarios are possible in this regime. We then compute one-loop quantum
corrections to the inflationary power spectrum. These are largest with N
spectator fields and a single participator field, and the resulting bound on N
is always weaker than those obtained in other ways. We find that loop
corrections to the N-flation power spectrum do not scale with N, and thus place
no upper bound on the number of participator fields. This result also implies
that, at least to leading order, the theory behaves like a composite single
scalar field. In order to perform this calculation, we address a number of
issues associated with loop calculations in the Schwinger-Keldysh "in-in"
formalism.Comment: Typos corrected. Matches published versio
Nonperturbative calculation of the anomalous magnetic moment in the Yukawa model within truncated Fock space
Within the covariant formulation of light-front dynamics, we calculate the
state vector of a physical fermion in the Yukawa model. The state vector is
decomposed in Fock sectors and we consider the first three ones: the single
constituent fermion, the constituent fermion coupled to one scalar boson, and
the constituent fermion coupled to two scalar bosons. This last three-body
sector generates nontrivial and nonperturbative contributions to the state
vector, which are calculated numerically. Field-theoretical divergences are
regularized using Pauli-Villars fermion and boson fields. Physical observables
can be unambiguously deduced using a systematic renormalization scheme we have
developed previously. As a first application, we consider the anomalous
magnetic moment of the physical fermion.Comment: 24 pages, 16 figure
Gauge Coupling Beta Functions in the Standard Model to Three Loops
In this paper we compute the three-loop corrections to the beta functions of
the three gauge couplings in the Standard Model of particle physics using the
minimal subtraction scheme and taking into account Yukawa and Higgs self
couplings.Comment: 4 pages, 1 figure, v2: minor changes, references adde
Anomaly Matching Conditions in Supersymmetric Gauge Theories
Sufficient conditions are proven for 't Hooft's consistency conditions to
hold at points in the moduli space of supersymmetric gauge theories. Known
results for anomaly matching in supersymmetric QCD are rederived as a sample
application of the results. The results can be used to show that the anomaly
matching conditions hold for s-confining theories.Comment: 14 pages, revte
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