4,837 research outputs found
Dirac equation in the confining SU(3)-Yang-Mills field and the relativistic effects in quarkonia spectra
The recently obtained solutions of Dirac equation in the confining
SU(3)-Yang-Mills field in Minkowski spacetime are applied to describe the
energy spectra of quarkonia (charmonium and bottomonium). The nonrelativistic
limit is considered for the relativistic effects to be estimated in a
self-consistent way and it is shown that the given effects are extremely
important for both the energy spectra and the confinement mechanism.Comment: 11 pages, LaTe
Hadronic Equation of State and Speed of Sound in Thermal and Dense Medium
The equation of state and speed of sound squared are
studied in grand canonical ensemble of all hadron resonances having masses
GeV. This large ensemble is divided into strange and non-strange
hadron resonances and furthermore to pionic, bosonic and femionic sectors. It
is found that the pions represent the main contributors to and other
thermodynamic quantities including the equation of state at low
temperatures. At high temperatures, the main contributions are added in by the
massive hadron resonances. The speed of sound squared can be calculated from
the derivative of pressure with respect to the energy density, , or from the entropy-specific heat ratio, . It is
concluded that the physics of these two expressions is not necessarily
identical. They are distinguishable below and above the critical temperature
. This behavior is observed at vanishing and finite chemical potential. At
high temperatures, both expressions get very close to each other and both of
them approach the asymptotic value, . In the HRG results, which are only
valid below , the difference decreases with increasing the temperature and
almost vanishes near . It is concluded that the HRG model can very well
reproduce the results of the lattice quantum chromodynamics (QCD) of and , especially at finite chemical potential. In
light of this, energy fluctuations and other collective phenomena associated
with the specific heat might be present in the HRG model. At fixed
temperatures, it is found that is not sensitive to the chemical
potential.Comment: 19 pages, 6 figures with 13 eps graph
Unstable particle's wave-function renormalization prescription
We strictly define two set Wave-function Renormalization Constants (WRC)
under the LSZ reduction formula for unstable particles at the first time. Then
by introducing antiparticle's WRC and the CPT conservation law we obtain a new
wave-function renormalization condition which can be used to totally determine
the two set WRC. We calculate two physical processes to manifest the
consistence of the present wave-function renormalization prescription with the
gauge theory in standard model. We also prove that the conventional
wave-function renormalization prescription which discards the imaginary part of
unstable particle's WRC leads to physical amplitude gauge dependent.Comment: 10 pages, 3 figure
New Recursion Relations and a Flat Space Limit for AdS/CFT Correlators
We consider correlation functions of the stress-tensor or a conserved current
in AdS_{d+1}/CFT_d computed using the Hilbert or the Yang-Mills action in the
bulk. We introduce new recursion relations to compute these correlators at tree
level. These relations have an advantage over the BCFW-like relations described
in arXiv:1102.4724 and arXiv:1011.0780 because they can be used in all
dimensions including d=3. We also introduce a new method of extracting
flat-space S-matrix elements from AdS/CFT correlators in momentum space. We
show that the (d+1)-dimensional flat-space amplitude of gravitons or gluons can
be obtained as the coefficient of a particular singularity of the d-dimensional
correlator of the stress-tensor or a conserved current; this technique is valid
even at loop-level in the bulk. Finally, we show that our recursion relations
automatically generate correlators that are consistent with this observation:
they have the expected singularity and the flat-space gluon or graviton
amplitude appears as its coefficient.Comment: 22+6 pages (v2) typos fixe
Spin constraints on Regge predictions and perturbative evolution in high energy collisions
Two key issues in the application of perturbative QCD and Regge predictions
to high energy processes are whether the hard and soft pomerons should be
considered as two separate distinct exchanges and whether the Regge intercepts
are Q^2 independent or not. Models involving a distinct hard pomeron exchange
predict much larger values for the LHC total cross-section. Here we argue that
there is a polarized analogue of this issue in the isovector part of the spin
structure function g_1 and that the spin data appear to favour a distinct hard
exchange.Comment: 8 page
Nuclear G-Matrix Elements from Nonlocal Potentials
We study effects of nonlocality in the nuclear force on the G-matrix elements
for finite nuclei. Nuclear G-matrix elements for \O16 are calculated in the
harmonic oscillator basis from a nonlocal potential which models quark exchange
effects between two nucleons. We employ a simple form of potential that gives
the same phase shifts as a realistic local nucleon potential. The G-matrix
elements calculated from the nonlocal potential show moderate increase in
repulsion from those derived from the local potential.Comment: 11 page, LaTeX, 2 PS figures, uses epsf.st
Constructing Gravity Amplitudes from Real Soft and Collinear Factorisation
Soft and collinear factorisations can be used to construct expressions for
amplitudes in theories of gravity. We generalise the "half-soft" functions used
previously to "soft-lifting" functions and use these to generate tree and
one-loop amplitudes. In particular we construct expressions for MHV tree
amplitudes and the rational terms in one-loop amplitudes in the specific
context of N=4 supergravity. To completely determine the rational terms
collinear factorisation must also be used. The rational terms for N=4 have a
remarkable diagrammatic interpretation as arising from algebraic link diagrams.Comment: 18 pages, axodraw, Proof of eq. 4.3 adde
Exploring the S-Matrix of Massless Particles
We use the recently proposed generalised on-shell representation for
scattering amplitudes and a consistency test to explore the space of tree-level
consistent couplings in four-dimensional Minkowski spacetime. The extension of
the constructible notion implied by the generalised on-shell representation,
i.e. the possibility to reconstruct at tree level all the scattering amplitudes
from the three-particle ones, together with the imposition of the consistency
conditions at four-particle level, allow to rediscover all the known theories
and their algebra structure, if any. Interestingly, this analysis seems to
leave room for high-spin couplings, provided that at least the requirement of
locality is weakened. We do not claim to have found tree-level consistent
high-spin theories, but rather that our methods show signatures of them and
very likely, with a suitable modification, they can be a good framework to
perform a systematic search.Comment: 44 pages, 1 figur
Trident pair production in strong laser pulses
We calculate the trident pair production amplitude in a strong laser
background. We allow for finite pulse duration, while still treating the laser
fields nonperturbatively in strong-field QED. Our approach reveals explicitly
the individual contributions of the one-step and two-step processes. We also
expose the role gauge invariance plays in the amplitudes and discuss the
relation between our results and the optical theorem.Comment: 4 pages, 1 .eps figure. Version 2: reference added, published versio
Unified Chew-Mandelstam SAID analysis of pion photoproduction data
A unified description of single-pion photoproduction data, together with
pion- and eta-hadroproduction data, has been achieved in a Chew-Mandelstam
parametrization which is consistent with unitarity at the two-body level.
Energy-dependent and single-energy partial wave analyses of pion
photoproduction data have been performed and compared to previous SAID fits and
multipoles from the Mainz and Bonn-Gatchina groups.Comment: 11 pages, 9 figures, and 2 table
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