2,123 research outputs found
Isospin dependence of the three-nucleon force
We classify --nucleon forces according to their isospin dependence and
discuss the most general isospin structure of the three--nucleon force. We
derive the leading and subleading isospin--breaking corrections to the
three--nucleon force using the framework of chiral effective field theory.Comment: 21 pages, 6 figure
Order by disorder and gauge-like degeneracy in quantum pyrochlore antiferromagnet
The (three-dimensional) pyrochlore lattice antiferromagnet with Heisenberg
spins of large spin length is a highly frustrated model with an macroscopic
degeneracy of classical ground states. The zero-point energy of (harmonic
order) spin wave fluctuations distinguishes a subset of these states. I derive
an approximate but illuminating {\it effective Hamiltonian}, acting within the
subspace of Ising spin configurations representing the {\it collinear} ground
states. It consists of products of Ising spins around loops, i.e has the form
of a lattice gauge theory. The remaining ground state entropy is still
infinite but not extensive, being for system size . All these
ground states have unit cells bigger than those considered previously.Comment: 4pp, one figur
Spin of ground state baryons
We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page
Phason elasticity of a three-dimensional quasicrystal: transfer-matrix method
We introduce a new transfer matrix method for calculating the thermodynamic
properties of random-tiling models of quasicrystals in any number of
dimensions, and describe how it may be used to calculate the phason elastic
properties of these models, which are related to experimental measurables such
as phason Debye-Waller factors, and diffuse scattering wings near Bragg peaks.
We apply our method to the canonical-cell model of the icosahedral phase,
making use of results from a previously-presented calculation in which the
possible structures for this model under specific periodic boundary conditions
were cataloged using a computational technique. We give results for the
configurational entropy density and the two fundamental elastic constants for a
range of system sizes. The method is general enough allow a similar calculation
to be performed for any other random tiling model.Comment: 38 pages, 3 PostScript figures, self-expanding uuencoded compressed
tar file, LaTeX using RevTeX macros and epsfig.st
The Nucleon-Mass Difference in Chiral Perturbation Theory and Nuclear Forces
A new method is developed for treating the effect of the neutron-proton mass
difference in isospin-violating nuclear forces. Previous treatments utilized an
awkward subtraction scheme to generate these forces. A field redefinition is
used to remove that mass difference from the Lagrangian (and hence from
asymptotic nucleon states) and replace its effect by effective interactions.
Previous calculations of static Class II charge-independence-breaking and Class
III charge-symmetry-breaking potentials are verified using the new scheme,
which is also used to calculate Class IV nuclear forces. Two-body forces of the
latter type are found to be identical to previously obtained results. A novel
three-body force is also found. Problems involving Galilean invariance with
Class IV one-pion-exchange forces are identified and resolved.Comment: 20 pages, 2 figures, latex - submitted to Physical Review
Charge-Symmetry-Breaking Three-Nucleon Forces
Leading-order three-nucleon forces that violate isospin symmetry are
calculated in Chiral Perturbation Theory. The effect of the
charge-symmetry-breaking three-nucleon force is investigated in the trinucleon
systems using Faddeev calculations. We find that the contribution of this force
to the 3He - 3H binding-energy difference is approximately 5 keV.Comment: 14 pages, 3 figure
Gravity Duals of Lifshitz-like Fixed Points
We find candidate macroscopic gravity duals for scale-invariant but
non-Lorentz invariant fixed points, which do not have particle number as a
conserved quantity. We compute two-point correlation functions which exhibit
novel behavior relative to their AdS counterparts, and find holographic
renormalization group flows to conformal field theories. Our theories are
characterized by a dynamical critical exponent , which governs the
anisotropy between spatial and temporal scaling , ; we focus on the case with . Such theories describe
multicritical points in certain magnetic materials and liquid crystals, and
have been shown to arise at quantum critical points in toy models of the
cuprate superconductors. This work can be considered a small step towards
making useful dual descriptions of such critical points.Comment: 17 pages, harvmac; v2 comments about behavior of metric near r=0
added (thanks to S. Hartnoll and G. Horowitz
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