1,077 research outputs found
High Energy Theorems at Large-N
Sum rules for products of two, three and four QCD currents are derived using
chiral symmetry at infinite momentum in the large-N limit. These exact
relations among meson decay constants, axialvector couplings and masses
determine the asymptotic behavior of an infinite number of QCD correlators. The
familiar spectral function sum rules for products of two QCD currents are among
the relations derived. With this precise knowledge of asymptotic behavior, an
infinite number of large-N QCD correlators can be constructed using dispersion
relations. A detailed derivation is given of the exact large-N pion vector form
factor and forward pion-pion scattering amplitudes.Comment: 34 pages TeX and mtexsis.tex, 10 figures (uses epsf
The Heavy Quark Spin Symmetry Partners of the X(3872)
We explore the consequences of heavy quark spin symmetry for the charmed
meson-antimeson system in a contact-range (or pionless) effective field theory.
As a trivial consequence, we theorize the existence of a heavy quark spin
symmetry partner of the X(3872), with , which we call X(4012) in
reference to its predicted mass. If we additionally assume that the X(3915) is
a heavy spin symmetry partner of the X(3872), we end up predicting a
total of six molecular states. We also discuss the error
induced by higher order effects such as finite heavy quark mass corrections,
pion exchanges and coupled channels, allowing us to estimate the expected
theoretical uncertainties in the position of these new states.Comment: 18 pages; final version accepted for publicatio
Making it in academic psychology: Demographic and personality correlates of eminence
Citations to published work, personality, and demographic characteristics were examined in a sample of male and female academic psychologists. A large sex difference was found in citations with men receiving significantly more recognition. Reputational rankings of graduate school and current institution were significantly related to citations, as were components of achievement motivation. Mastery and work needs were positively related to citations while competitiveness was negatively associated with the criterion. A model of attainment in psychology is proposed and possible explanations for the differential recognition of women are explored
Unitarity constraint for threshold coherent pion photoproduction on the deuteron and chiral perturbation theory
The contribution of the two-step process gamma + d -> p + n -> pi0 + d to the
imaginary part of the amplitude for coherent pion production on the deuteron is
calculated exploiting unitarity constraints. The result shows that this
absorptive process is not negligible and has to be considered in an extraction
of the elementary neutron production amplitude from the gamma + d -> pi0 + d
cross section at threshold. In addition, it is argued that a consistent
calculation of gamma + d -> pi0 + d in baryon chiral perturbation theory beyond
next-to-leading order requires the inclusion of this absorptive process.Comment: 11 pages revtex including 2 postscript figure
How quantum bound states bounce and the structure it reveals
We investigate how quantum bound states bounce from a hard surface. Our
analysis has applications to ab initio calculations of nuclear structure and
elastic deformation, energy levels of excitons in semiconductor quantum dots
and wells, and cold atomic few-body systems on optical lattices with sharp
boundaries. We develop the general theory of elastic reflection for a composite
body from a hard wall. On the numerical side we present ab initio calculations
for the compression of alpha particles and universal results for two-body
states. On the analytical side we derive a universal effective potential that
gives the reflection scattering length for shallow two-body states.Comment: final publication version, new lattice results on alpha particle
compression, 5 pages, 2 figure
A Theoretical Investigation of the Drag of Generalized Aircraft Configurations in Supersonic Flow
It seems possible that, in supersonic flight, unconventional arrangements of wings and bodies may offer advantages in the form of drag reduction. It is the purpose of this report to consider the methods for determining the pressure drag for such unconventional configurations, and to consider a few of the possibilities for drag reduction in highly idealized aircraft. The idealized aircraft are defined by distributions of lift and volume in three-dimensional space, and Hayes' method of drag evaluation, which is well adapted to such problems, is the fundamental tool employed. Other methods of drag evaluation are considered also wherever they appear to offer amplifications. The basic singularities such as sources, dipoles, lifting elements and volume elements are discussed, and some of the useful inter-relations between these elements are presented. Hayes' method of drag evaluation is derived in detail starting with the general momentum theorem. In going from planar systems to spatial systems certain new problems arise. For example, interference between lift and thickness distributions generally appears, and such effects are used to explain the difference between the non-zero wave drag of Sears-Haack bodies and the zero wave drag of Ferrari's ring wing plus central body. Another new feature of the spatial systems is that optimum configurations generally are not unique, there being an infinite family of lift or thickness distributions producing the same minimum drag. However it is shown that all members of an optimum family produce the same flow field in a certain region external to the singularity distribution. Other results of the study indicate that certain spatial distributions may produce materially less wave drag and vortex drag than comparable planar systems. It is not at all certain that such advantages can be realized in practical aircraft designs, but further investigation seems to be warranted
High Statistics Analysis using Anisotropic Clover Lattices: (IV) Volume Dependence of Light Hadron Masses
The volume dependence of the octet baryon masses and relations among them are
explored with Lattice QCD. Calculations are performed with n_f=2+1 clover
fermion discretization in four lattice volumes, with spatial extent L ~ 2.0,
2.5, 3.0 and 3.9 fm, with an anisotropic lattice spacing of b_s ~ 0.123 fm in
the spatial direction, and b_t = b_s/3.5 in the time direction, and at a pion
mass of m_pi ~ 390 MeV. The typical precision of the ground-state baryon mass
determination is ~0.2%, enabling a precise exploration of the volume dependence
of the masses, the Gell-Mann--Okubo mass relation, and of other mass
combinations. A comparison of the volume dependence with the predictions of
heavy baryon chiral perturbation theory is performed in both the SU(2)_L X
SU(2)_R and SU(3)_L X SU(3)_R expansions. Predictions of the three-flavor
expansion for the hadron masses are found to describe the observed volume
dependences reasonably well. Further, the Delta-N-pi axial coupling constant is
extracted from the volume dependence of the nucleon mass in the two-flavor
expansion, with only small modifications in the three-flavor expansion from the
inclusion of kaons and etas. At a given value of m_pi L, the finite-volume
contributions to the nucleon mass are predicted to be significantly smaller at
m_pi ~ 140 MeV than at m_pi ~ 390 MeV due to a coefficient that scales as ~
m_pi^3. This is relevant for the design of future ensembles of lattice
gauge-field configurations. Finally, the volume dependence of the pion and kaon
masses are analyzed with two-flavor and three-flavor chiral perturbation
theory.Comment: 34 pages, 45 figure
Deriving the existence of bound states from the X(3872) and Heavy Quark Symmetry
We discuss the possibility and the description of bound states between
and mesons. We argue that the existence of such a bound state can
be deduced from (i) the weakly bound X(3872) state, (ii) certain assumptions
about the short range dynamics of the system and (iii) heavy quark
symmetry. From these assumptions the binding energy of the possible
bound states is determined, first in a theory containing only
contact interactions which serves as a straightforward illustration of the
method, and then the effects of including the one pion exchange potential are
discussed. In this latter case three isoscalar states are predicted: a positive
and negative C-parity state with a binding energy of and below threshold respectively, and a positive C-parity
shallow state located almost at the threshold. However,
large uncertainties are generated as a consequence of the corrections
from heavy quark symmetry. Finally, the newly discovered isovector
state can be easily accommodated within the present framework by a minor
modification of the short range dynamics.Comment: 21 pages, 3 figures; a sign error in the potential has been corrected
and new predictions have been compute
Present Constraints on the H-dibaryon at the Physical Point from Lattice QCD
The current constraints from lattice QCD on the existence of the H-dibaryon
are discussed. With only two significant lattice QCD calculations of the
H-dibaryon binding energy at approximately the same lattice spacing, the forms
of the chiral and continuum extrapolations to the physical point are not
determined. In this brief report, we consider the constraints on the H-dibaryon
imposed by two simple chiral extrapolations. In both instances, the
extrapolation to the physical pion mass allows for a bound H-dibaryon or a
near-threshold scattering state. Further lattice QCD calculations are required
to clarify this situation.Comment: 8 pages, 2 figures, 1 table; revised for the journa
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