78 research outputs found
Symmetries of hadrons after unbreaking the chiral symmetry
We study hadron correlators upon artificial restoration of the spontaneously
broken chiral symmetry. In a dynamical lattice simulation we remove the lowest
lying eigenmodes of the Dirac operator from the valence quark propagators and
study evolution of the hadron masses obtained. All mesons and baryons in our
study, except for a pion, survive unbreaking the chiral symmetry and their
exponential decay signals become essentially better. From the analysis of the
observed spectroscopic patterns we conclude that confinement still persists
while the chiral symmetry is restored. All hadrons fall into different chiral
multiplets. The broken U(1)_A symmetry does not get restored upon unbreaking
the chiral symmetry. We also observe signals of some higher symmetry that
includes chiral symmetry as a subgroup. Finally, from comparison of the \Delta
- N splitting before and after unbreaking of the chiral symmetry we conclude
that both the color-magnetic and the flavor-spin quark-quark interactions are
of equal importance.Comment: 12 pages, 14 figures; final versio
Bianchi Type I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity
Bianchi type I massive string cosmological model with magnetic field of
barotropic perfect fluid distribution through the techniques used by Latelier
and Stachel, is investigated. To get the deterministic model of the universe,
it is assumed that the universe is filled with barotropic perfect fluid
distribution. The magnetic field is due to electric current produced along
x-axis with infinite electrical conductivity. The behaviour of the model in
presence and absence of magnetic field together with other physical aspects is
further discussed.Comment: 10 pages, no figure. Chin. Phys. Lett., Vol. 24, No. 8 (2007), to
appea
Bianchi Type III String Cosmological Models with Time Dependent Bulk Viscosity
Bianchi type III string cosmological models with bulk viscous fluid for
massive string are investigated. To get the determinate model of the universe,
we have assumed that the coefficient of bulk viscosity () is inversely
proportional to the expansion () in the model and expansion ()
in the model is proportional to the shear (). This leads to , and are constants. The behaviour of the model in presence
and absence of bulk viscosity, is discussed. The physical implications of the
models are also discussed in detail.Comment: 11 pages, no figur
Chiral symmetry restoration in excited hadrons, quantum fluctuations, and quasiclassics
In this paper, we discuss the transition to the semiclassical regime in
excited hadrons, and consequently, the restoration of chiral symmetry for these
states. We use a generalised Nambu-Jona-Lasinio model with the interaction
between quarks in the form of the instantaneous Lorentz-vector confining
potential. This model is known to provide spontaneous breaking of chiral
symmetry in the vacuum via the standard selfenergy loops for valence quarks. It
has been shown recently that the effective single-quark potential is of the
Lorentz-scalar nature, for the low-lying hadrons, while, for the high-lying
states, it becomes a pure Lorentz vector and hence the model exhibits the
restoration of chiral symmetry. We demonstrate explicitly the quantum nature of
chiral symmetry breaking, the absence of chiral symmetry breaking in the
classical limit as well as the transition to the semiclassical regime for
excited states, where the effect of chiral symmetry breaking becomes only a
small correction to the classical contributions.Comment: RevTeX4, 20 pages, 4 Postscript figures, uses epsfig.sty, typos
correcte
Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter
The present study deals with a spatially homogeneous and anisotropic
Bianchi-II cosmological models representing massive strings in normal gauge for
Lyra's manifold by applying the variation law for generalized Hubble's
parameter that yields a constant value of deceleration parameter. The variation
law for Hubble's parameter generates two types of solutions for the average
scale factor, one is of power-law type and other is of the exponential form.
Using these two forms, Einstein's modified field equations are solved
separately that correspond to expanding singular and non-singular models of the
universe respectively. The energy-momentum tensor for such string as formulated
by Letelier (1983) is used to construct massive string cosmological models for
which we assume that the expansion () in the model is proportional to
the component of the shear tensor . This
condition leads to , where A, B and C are the metric coefficients
and m is proportionality constant. Our models are in accelerating phase which
is consistent to the recent observations. It has been found that the
displacement vector behaves like cosmological term in the
normal gauge treatment and the solutions are consistent with recent
observations of SNe Ia. It has been found that massive strings dominate in the
decelerating universe whereas strings dominate in the accelerating universe.
Some physical and geometric behaviour of these models are also discussed.Comment: 24 pages, 10 figure
The Gluon Exchange Interaction Between Constituent Quarks
The interaction mediated by irreducible pion and gluon exchange between
constituent quarks is calculated and shown to have a strong tensor component,
which tends to cancel the pion exchange tensor interaction between quarks. Its
spin-spin component is somewhat weaker than the pion exchange spin-spin
interaction, while its central and spin-orbit components are small in
comparison to the corresponding single gluon exchange interactions. The
combination of the gluon exchange interaction with the single pion
exchange interaction and a weak gluon exchange interaction between constituent
quarks has the qualitative features required for understanding the hyperfine
splittings of the spectra of the nucleon and the resonances.Comment: LaTeX, 17 pages, 5 Postscript figure
Bianchi Type I Magnetofluid Cosmological Models with Variable Cosmological Constant Revisited
The behaviour of magnetic field in anisotropic Bianchi type I cosmological
model for bulk viscous distribution is investigated. The distribution consists
of an electrically neutral viscous fluid with an infinite electrical
conductivity. It is assumed that the component of shear tensor
is proportional to expansion () and the coefficient of
bulk viscosity is assumed to be a power function of mass density. Some physical
and geometrical aspects of the models are also discussed in presence and also
in absence of the magnetic field.Comment: 13 page
Critique of a Pion Exchange Model for Interquark Forces
I describe four serious defects of a widely discussed pion exchange model for
interquark forces: it doesn't solve the "spin-orbit problem" as advertised, it
fails to describe the internal structure of baryon resonances, it leads to
disastrous conclusions when extended to mesons, and it is not reasonably
connected to the physics of heavy-light systems.Comment: 20 pages, 6 figures; some clarifications and references adde
All-charm tetraquarks
We investigate four-body states with only charm quarks. Working in a large
but finite oscillator basis, we present a net binding analysis to determine if
the resulting states are stable against breakup into a pair of c-cbar mesons.
We find several close-lying bound states in the two models we examine.Comment: 24 pgs, 10 table
Bianchi type-I string cosmological model in the presence of a magnetic flux: exact and qualitative solutions
A Bianchi type-I cosmological model in the presence of a magnetic flux along
a cosmological string is investigated. The objective of this study is to
generate solutions to the Einstein equations using a few tractable assumptions
usually accepted in the literature. The analytical solutions are supplemented
with numerical and qualitative analysis. In the frame of the present model the
evolution of the Universe and other physical aspects are discussed.Comment: 13 pages, 6 figure
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