10,945 research outputs found
Perturbation of a lattice spectral band by a nearby resonance
A soluble model of weakly coupled "molecular" and "nuclear" Hamiltonians is
studied in order to exhibit explicitly the mechanism leading to the enhancement
of fusion probability in case of a narrow near-threshold nuclear resonance. We,
further, consider molecular cells of this type being arranged in lattice
structures. It is shown that if the real part of the narrow nuclear resonance
lies within the molecular band generated by the intercellular interaction, an
enhancement, proportional to the inverse width of the nuclear resonance, is to
be expected.Comment: RevTeX, 2 figures within the file. In May 2000 the title changed and
some minor corrections have been don
Pair production of charged Higgs scalars from electroweak gauge boson fusion
We compute the contribution to charged Higgs boson pair production at the
Large Hadron Collider (LHC) due to the scattering of two electroweak (EW) gauge
bosons, these being in turn generated via bremsstrahlung off incoming quarks: q
q --> q q V^*V^* --> q q H^+H^- (V=gamma,Z,W^{+/-}). We verify that the
production cross section of this mode is tan beta independent and show that it
is smaller than that of H^+H^- production via q q-initiated processes but
generally larger than that of the loop-induced channel gg --> H^+H^-. Pair
production of charged Higgs bosons is crucial in order to test EW symmetry
breaking scenarios beyond the Standard Model (SM). We show that the detection
of these kind of processes at the standard LHC is however problematic, because
of their poor production rates and the large backgrounds.Comment: 22 pages, latex, 8 figures (largely revised version to appear in JPG
Semileptonic to Nucleon Transitions in Full QCD at Light Cone
The tree level semileptonic and
transitions are investigated using the light cone QCD sum rules approach in
full theory. The spin--1/2, baryon with or , is
considered by the most general form of its interpolating current. The time
ordering product of the initial and transition currents is expanded in terms of
the nucleon distribution amplitudes with different twists. Considering two sets
of independent input parameters entering to the nucleon wave functions, namely,
QCD sum rules and Lattice QCD parameters, the related form factors and their
heavy quark effective theory limits are calculated and compared with the
existing predictions of other approaches. It is shown that our results satisfy
the heavy quark symmetry relations for lattice input parameters and b case
exactly and the maximum violation is for charm case and QCD sum rules input
parameters. The obtained form factors are used to compute the transition rates
both in full theory and heavy quark effective theory. A comparison of the
results on decay rate of with those predicted by other
phenomenological methods or the same method in heavy quark effective theory
with different interpolating current and distribution amplitudes of the
is also presented.Comment: 18 Pages and 16 Table
Flavor Changing Neutral Currents Transition of the to Nucleon in Full QCD and Heavy Quark Effective Theory
The loop level flavor changing neutral currents transitions of the
and are investigated in full
QCD and heavy quark effective theory in the light cone QCD sum rules approach.
Using the most general form of the interpolating current for ,
or , as members of the recently discovered sextet heavy baryons with
spin 1/2 and containing one heavy quark, the transition form factors are
calculated using two sets of input parameters entering the nucleon distribution
amplitudes, namely, QCD sum rules and lattice QCD inputs. The obtained results
are used to estimate the decay rates of the corresponding transitions. Since
such type transitions occurred at loop level in the standard model, they can be
considered as good candidates to search for the new physics effects beyond the
SM.Comment: 18 Pages and 13 Table
The supermultiplet of boundary conditions in supergravity
Boundary conditions in supergravity on a manifold with boundary relate the
bulk gravitino to the boundary supercurrent, and the normal derivative of the
bulk metric to the boundary energy-momentum tensor. In the 3D N=1 setting, we
show that these boundary conditions can be stated in a manifestly
supersymmetric form. We identify the Extrinsic Curvature Tensor Multiplet, and
show that boundary conditions set it equal to (a conjugate of) the boundary
supercurrent multiplet. Extension of our results to higher-dimensional models
(including the Randall-Sundrum and Horava-Witten scenarios) is discussed.Comment: 22 pages. JHEP format; references added; published versio
Four-quark spectroscopy within the hyperspherical formalism
We present a generalization of the hyperspherical harmonic formalism to study
systems made of quarks and antiquarks of the same flavor. This generalization
is based on the symmetrization of the body wave function with respect to
the symmetric group using the Barnea and Novoselsky algorithm. The formalism is
applied to study four-quark systems by means of a constituent quark model
successful in the description of the two- and three-quark systems. The results
are compared to those obtained by means of variational approaches. Our analysis
shows that four-quark systems with exotic and non-exotic
quantum numbers may be bound independently of the mass of the quark.
and states become attractive only for larger mass of the quarks.Comment: 20 pages, 3 figure
Strong coupling constants of bottom and charmed mesons with scalar, pseudoscalar and axial vector kaons
The strong coupling constants, , ,
, , and
, where , and are scalar, pseudoscalar
and axial vector kaon mesons, respectively are calculated in the framework of
three-point QCD sum rules. In particular, the correlation functions of the
considered vertices when both and mesons are off-shell
are evaluated. In the case of , which is either or
, the mixing between these two states are also taken into account. A
comparison of the obtained result with the existing prediction on
as the only coupling constant among the considered
vertices, previously calculated in the literature, is also made.Comment: 20 Pages, 3 Figures and 8 Table
Decays with Corrections in Factorization
It is commonly believed that a careful investigation of the subleading terms
is crucial for a better understanding of the factorization in charmless B
decays. In this work the penguin-dominated decays are discussed
systematically, including the subleading corrections in due to soft and
hard gluons, besides the annihilation contributions. Soft-gluon effects for all
the relevant 4-quark effective operators are calculated within the framework of
the light-cone QCD sum rules (LCSR). Our observation is that such soft and hard
corrections are less important than the annihilation effects, enhancing only
the branching ratios by a few percent; the resultant increase in the branching
ratios due to the overall effects is between about
of the QCD factorization results with the corrections, as
the weak phase ranges from to .
Impacts of the involved uncertainties are discussed in some details.Comment: 22 pages,6 figure
Hot Gauge Theories and Phases
In this paper the several aspects of the symmetry in gauge theories
at high temperatures are discussed. The metastable bubbles in the
gauge theories with fermions may have, generically, unacceptable
thermodynamic behavior. Their free energy with a positive
proportionality constant. This leads not only to negative pressure but also to
negative specific heat and, more seriously, to negative entropy. We argue that
although such domains are important in the Euclidean theory, they cannot be
interpreted as physical domains in Minkowski space. The related problem is
connected with the analysis of the high-temperature limit of the confining
phase. Using the two-dimensional QCD with adjoint fermions as a toy model we
shall demonstrate that in the light fermion limit in this theory there is no
breaking of the symmetry in the high-temperature limit and thus there
are no bubbles.Comment: preprint PUPT-1415, 21
Scalars from Top-condensation Models at Hadron Colliders
We study the production and decay of neutral scalars and pseudo-scalars at
hadron colliders, in theories where the top-quark mass is the result of a
condensate. We show that the dominant decay channel for masses below
the threshold is the flavor changing mode . This is a consequence
of the non-universal nature of the underlying interactions in all
top-condensation models and provides a model-independent signature of these
scenarios. We show that an upgraded Tevatron is sensitive to a sizeable region
of the interesting parameter space and that the LHC will highly constrain these
models through this flavor violating channel.Comment: 4 pages, 4 figures. Minor changes in figures for readibility. final
version to appear in PR
- …