716 research outputs found
Calibrated Surfaces and Supersymmetric Wilson Loops
We study the dual gravity description of supersymmetric Wilson loops whose
expectation value is unity. They are described by calibrated surfaces that end
on the boundary of anti de-Sitter space and are pseudo-holomorphic with respect
to an almost complex structure on an eight-dimensional slice of AdS_5 x S^5.
The regularized area of these surfaces vanishes, in agreement with field theory
non-renormalization theorems for the corresponding operators.Comment: 28 pages, 2 figure
QCD Mass Inequalities in the Heavy Quark Limit
QCD inequalities are derived for the masses of mesons and baryons containing
a single heavy quark using the heavy quark effective field theory. A rigorous
lower bound is obtained for the parameters of the heavy quark
effective theory that parameterize corrections, > 237 MeV
for mesons, and MeV for baryons. The inequalities on
imply the inequalities MeV and MeV for
the mass parameters of the heavy quark effective field theory.Comment: 10 pages, 0 figures, uses harvma
Properties of Baryons Containing a Heavy Quark in the Skyrme Model
The properties of baryons containing one heavy quark are studied in the
Skyrme model, where they are treated as bound states of a heavy meson with an
chiral soliton. In the large limit, the baryon spectrum is an
infinite tower of degenerate states with isospin and spin of the light degrees
of freedom , and total spin s=\abs{s_\ell\pm1/2}.
Exotic states with no quark model analogues in the large limit are found
to be unbound. The mass difference is computed and found
to be in good agreement with experiment. The and
coupling constants are calculated to leading order
in in terms of , the axial coupling constant of the nucleon. We
discuss the extension of our results to chiral solitons.Comment: (28 pages, 0 figures, uses harvmac.tex
Baryon-Pion Couplings from Large-N QCD
We derive a set of consistency conditions for the pion-baryon coupling
constants in the large-N limit of QCD. The consistency conditions have a unique
solution which are precisely the values for the pion-baryon coupling constants
in the Skyrme model. We also prove that non-relativistic spin-flavor
symmetry (where is the number of light flavors) is a symmetry of the
baryon-pion couplings in the large-N limit of QCD. The symmetry breaking
corrections to the pion-baryon couplings vanish to first order in .
Consistency conditions for other couplings, such as the magnetic moments are
also derived.Comment: (12 pages, 2 figs, uses harvmac and uufiles), UCSD/PTH 93-1
The Baryon Isgur-Wise Function in the Large Limit
In the large limit, the and can be treated as
bound states of chiral solitons and mesons containing a heavy quark. We show
that the soliton and heavy meson are bound in an attractive harmonic oscillator
potential. The Isgur-Wise function for decay is computed in the large limit. Corrections to the
form factor which depend on can be summed exactly ( and
are the nucleon and heavy quark masses). We find that this symmetry breaking
correction at zero recoil is only .Comment: 18 pages, 0 figures, uses harvma
BPS Wilson Loops on S^2 at Higher Loops
We consider supersymmetric Wilson loops of the variety constructed by
Drukker, Giombi, Ricci, and Trancanelli, whose spatial contours lie on a
two-sphere. Working to second order in the 't Hooft coupling in planar N=4
Supersymmetric Yang-Mills Theory (SYM), we compute the vacuum expectation value
of a wavy-latitude and of a loop composed of two longitudes. We evaluate the
resulting integrals numerically and find that the results are consistent with
the zero-instanton sector calculation of Wilson loops in 2-d Yang-Mills on S^2
performed by Bassetto and Griguolo. We also consider the connected correlator
of two distinct latitudes to third order in the 't Hooft coupling in planar N=4
SYM. We compare the result in the limit where the latitudes become coincident
to a perturbative calculation in 2-d Yang-Mills on S^2 using a light-cone
Wu-Mandelstam-Leibbrandt prescription. We are not able to calculate the SYM
result at the required order in the separation between the latitudes necessary
for a match with 2-d Yang-Mills; the result, however, does not preclude such a
match.Comment: 39 pages, 15 figures. v2 references added, minor cosmetic changes. v3
minor error in eq. (40) corrected. v4 error in coincident limit of correlator
corrected; claims of disagreement with 2-d Yang-Mills retracte
Baryons Containing a Heavy Quark as Solitons
The possibility of interpreting baryons containing a single heavy quark as
bound states of solitons (that arise in the nonlinear sigma model) and heavy
mesons is explored. Particular attention is paid to the parity of the bound
states and to the role of heavy quark symmetry.Comment: 15 pages, uses phyzzx.tex and tables.tex, REVISED VERSION: Some of
the results have changed because of a crucial minus sign, CALT-68-1783 and
UCSD/PTH 92-1
Consistency in Regularizations of the Gauged NJL Model at One Loop Level
In this work we revisit questions recently raised in the literature
associated to relevant but divergent amplitudes in the gauged NJL model. The
questions raised involve ambiguities and symmetry violations which concern the
model's predictive power at one loop level. Our study shows by means of an
alternative prescription to handle divergent amplitudes, that it is possible to
obtain unambiguous and symmetry preserving amplitudes. The procedure adopted
makes use solely of {\it general} properties of an eventual regulator, thus
avoiding an explicit form. We find, after a thorough analysis of the problem
that there are well established conditions to be fulfiled by any consistent
regularization prescription in order to avoid the problems of concern at one
loop level.Comment: 22 pages, no figures, LaTeX, to appear in Phys.Rev.
Pair production of neutralinos via gluon-gluon collisions
The production of a neutralino pair via gluon-gluon fusion is studied in the
minimal supersymmetric model(MSSM) at proton-proton colliders. The numerical
analysis of their production rates are carried out in the mSUGRA scenario. The
results show that this cross section may reach about 80 femto barn for
pair production and 23 femto barn
for pair production with suitable
input parameters at the future LHC collider. It shows that this loop mediated
process can be competitive with the quark-antiquark annihilation process at the
LHC.Comment: LaTex file, l4 pages, 5 EPS figure
Dirac theory within the Standard-Model Extension
The modified Dirac equation in the Lorentz-violating Standard-Model Extension
(SME) is considered. Within this framework, the construction of a hermitian
Hamiltonian to all orders in the Lorentz-breaking parameters is investigated,
discrete symmetries and the first-order roots of the dispersion relation are
determined, and various properties of the eigenspinors are discussed.Comment: 11 pages REVTe
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