200 research outputs found
Renormalization of the one-pion-exchange interaction
A renormalization scheme for the nucleon-nucleon (NN) interaction based on a
subtracted T-matrix equation is proposed and applied to the one-pion-exchange
potential supplemented by contact interactions. The singlet and triplet
scattering lengths are given to fix the renormalized strengths of the contact
interactions. With only one scaling parameter (), the results show an
overall very good agreement with neutron-proton data, particularly for the
observables related to the triplet channel. The agreement is qualitative in the
channel. Between the low-energy NN observables we have examined, the
mixing parameter of the states is the most sensible to the scale.
The scheme is renormalization group invariant for .Comment: 16 pages, 4 eps figures, to appear in Nuclear Physics
Pertinent Dirac structure for QCD sum rules of meson-baryon coupling constants
Using general baryon interpolating fields for
without derivative, we study QCD sum rules for meson-baryon couplings and their
dependence on Dirac structures for the two-point correlation function with a
meson i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket.
Three distinct Dirac structures are compared: ,
i\gamma_5\fslash{p}, and structures.
From the dependence of the OPE on general baryon interpolating fields, we
propose criteria for choosing an appropriate Dirac structure for the coupling
sum rules. The sum rules satisfy the
criteria while the sum rules beyond the chiral limit do not. For
the i\gamma_5\fslash{p} sum rules, the large continuum contributions prohibit
reliable prediction for the couplings. Thus, the structure seems pertinent for realistic predictions. In the SU(3) limit,
we identify the OPE terms responsible for the ratio. We then study the
dependence of the ratio on the baryon interpolating fields. We conclude the
ratio for appropriate choice of the interpolating fields.Comment: To be published in Phys.Rev.C ; 21 pages,8 figures, revtex ;
references are adde
Electroweak Matrix Elements in the Two-Nucleon Sector from Lattice QCD
We demonstrate how to make rigorous predictions for electroweak matrix
elements in nuclear systems directly from QCD. More precisely, we show how to
determine the short-distance contributions to low-momentum transfer electroweak
matrix elements in the two-nucleon sector from lattice QCD. In potential model
descriptions of multi-nucleon systems, this is equivalent to uniquely
determining the meson-exchange currents, while in the context of nuclear
effective field theory, this translates into determining the coefficients of
local, gauge-invariant, multi-nucleon-electroweak current operators. The
energies of the lowest-lying states of two nucleons on a finite volume lattice
with periodic boundary conditions in the presence of a background magnetic
field are sufficient to determine the local four-nucleon operators that
contribute to the deuteron magnetic moment and to the threshold cross-section
of n + p -> d + gamma. Similarly, the energy-levels of two nucleons immersed in
a background isovector axial weak field can be used to determine the
coefficient of the leading local four-nucleon operator contributing to the
neutral- and charged-current break-up of the deuteron. This is required for the
extraction of solar neutrino fluxes at SNO and future neutrino experiments.Comment: 22 pages, 4 figure
Scheming in Dimensional Regularization
We consider the most general loop integral that appears in non-relativistic
effective field theories with no light particles. The divergences of this
integral are in correspondence with simple poles in the space of complex
space-time dimensions. Integrals related to the original integral by
subtraction of one or more poles in dimensions other than D=4 lead to
nonminimal subtraction schemes. Subtraction of all poles in correspondence with
ultraviolet divergences of the loop integral leads naturally to a
regularization scheme which is precisely equivalent to cutoff regularization.
We therefore recover cutoff regularization from dimensional regularization with
a nonminimal subtraction scheme. We then discuss the power-counting for
non-relativistic effective field theories which arises in these alternative
schemes.Comment: 12 pages, additional text in opening section, version to be published
in J. Phys.
Calculation of Ground State Energy for Confined Fermion Fields
A method for renormalization of the Casimir energy of confined fermion fields
in (1+1)D is proposed. It is based on the extraction of singularities which
appear as poles at the point of physical value of the regularization parameter,
and subsequent compensation of them by means of redefinition of the "bare"
constants. A finite ground state energy of the two-phase hybrid model of
fermion bag with chiral boson-fermion interaction is calculated as the function
of the bag's size.Comment: 10 pages, LaTeX; no figures. Version to appear in Phys. Lett. B
(2001
Collective modes and current-algebraic sum rules in nuclear medium
In-medium sum rules following from the chiral charge algebra of QCD are
reviewed, and new sum rules are derived. The new sum rules relate the
I^G(J^{PC})=1^-(0^{++}) excitations (quantum numbers of a_0(980)) to the scalar
and isovector densities, and are nontrivial for the isospin-asymmetric medium.
We present an extensive illustration of the sum rules with help of quark matter
in the Nambu-Jona--Lasinio model. Collective excitations different from the
usual meson branches (spin-isospin sound modes) are shown to contribute
significantly to the sum rules and to play a crucial role in the limit of
vanishing current quark masses.Comment: latex, elsart.sty, 32 pages, 11 figure
g_{\pi \Lambda \Sigma} and g_{K \Sigma \Xi} from QCD sum rules
The coupling constants g_{\pi \Lambda \Sigma} and g_{K \Sigma \Xi} are
calculated in the QCD sum rule approach using the three-point function method
and taking into account the SU(3) symmetry breaking effects. The pattern of
SU(3) breaking appears to be different from that based on SU(3) relations.Comment: revtex, 9 page
The ratio and meson-baryon couplings from QCD sum rules-II
Using QCD sum rules, we compute the diagonal meson-baryon couplings, , , , , and , from the baryon-baryon correlation function with a meson,
. The calculations
are performed to leading order in by considering the two separate Dirac
structures, and separately. We first improve the previous sum rule calculations on
these Dirac structures for the coupling by including three-particle
pion wave functions of twist 4 and then extend the formalism to calculate the
other couplings, , , ,
and . In the SU(3) symmetric limit, we identify the terms
responsible for the ratio in the OPE by matching the obtained couplings
with their SU(3) relations. Depending on the Dirac structure considered, we
find different identifications for the ratio. The couplings including the
SU(3) breaking effects are also discussed within our approach.Comment: 28 pages including 4 figures. slightly revised. accepted for
publication in Nuclear Physics
Chiral quark-soliton model in the Wigner-Seitz approximation
In this paper we study the modification of the properties of the nucleon in
the nucleus within the quark-soliton model. This is a covariant, dynamical
model, which provides a non-linear representation of the spontaneously broken
SU(2)_L X SU(2)_R symmetry of QCD. The effects of the nuclear medium are
accounted for by using the Wigner-Seitz approximation and therefore reducing
the complex many-body problem to a simpler single-particle problem. We find a
minimum in the binding energy at finite density, a change in the isoscalar
nucleon radius and a reduction of the in-medium pion decay constant. The latter
is consistent with a partial restoration of chiral symmetry at finite density,
which is predicted by other models.Comment: 30 pages, 13 figures; uses REVTeX and epsfi
Two-Pion Exchange Nucleon-Nucleon Potential: Model Independent Features
A chiral pion-nucleon amplitude supplemented by the HJS subthreshold
coefficients is used to calculate the the long range part of the two-pion
exchange nucleon-nucleon potential. In our expressions the HJS coefficients
factor out, allowing a clear identification of the origin of the various
contributions. A discussion of the configuration space behaviour of the loop
integrals that determine the potential is presented, with emphasis on
cancellations associated with chiral symmetry. The profile function for the
scalar-isoscalar component of the potential is produced and shown to disagree
with those of several semi-phenomenological potentials.Comment: 16 pages, 9 embedded figures, Latex 2.09, Revtex.sty, epsf.st
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