347 research outputs found
Measurement of stopping beam distributions in the PIBETA detector
Precise calculation of the geometrical acceptance of a large solid angle
detector with an integrated stopping target relies on precise knowledge of the
beam geometry. We describe four alternative methods that we used to measure the
beam stopping distributions in the PIBETA detector active target: (i) light
response of segmented target elements to incident beam particles, (ii)
back-tracking of charged particles from pi+ and mu+ decays using multi-wire
proportional chambers, (iii) volume distribution of the Dalitz decay
(pi0->gamma e+e-) event vertices, and (iv) the opening angle distribution of
two pi0 photons originating from the beta decay of pi+ at rest. We demonstrate
consistent results obtained by these four independent approaches and show how
particular beam stopping distributions affect the detector's geometrical
acceptance.Comment: 38 pages, 16 postscript figures, 2 tables, LaTeX, submitted to Nucl.
Instrum. Meth.
Twisted supersymmetric 5D Yang-Mills theory and contact geometry
We extend the localization calculation of the 3D Chern-Simons partition
function over Seifert manifolds to an analogous calculation in five dimensions.
We construct a twisted version of N=1 supersymmetric Yang-Mills theory defined
on a circle bundle over a four dimensional symplectic manifold. The notion of
contact geometry plays a crucial role in the construction and we suggest a
generalization of the instanton equations to five dimensional contact
manifolds. Our main result is a calculation of the full perturbative partition
function on a five sphere for the twisted supersymmetric Yang-Mills theory with
different Chern-Simons couplings. The final answer is given in terms of a
matrix model. Our construction admits generalizations to higher dimensional
contact manifolds. This work is inspired by the work of Baulieu-Losev-Nekrasov
from the mid 90's, and in a way it is covariantization of their ideas for a
contact manifold.Comment: 28 pages; v2: minor mistake corrected; v3: matches published versio
Phases of planar 5-dimensional supersymmetric Chern-Simons theory
In this paper we investigate the large- behavior of 5-dimensional
super Yang-Mills with a level Chern-Simons term and an
adjoint hypermultiplet. As in three-dimensional Chern-Simons theories, one must
choose an integration contour to completely define the theory. Using
localization, we reduce the path integral to a matrix model with a cubic action
and compute its free energy in various scenarios. In the limit of infinite
Yang-Mills coupling and for particular choices of the contours, we find that
the free-energy scales as for gauge groups with large values
of the Chern-Simons 't\,Hooft coupling, . If we also
set the hypermultiplet mass to zero, then this limit is a superconformal fixed
point and the behavior parallels other fixed points which have known
supergravity duals. We also demonstrate that gauge groups cannot have
this scaling for their free-energy. At finite Yang-Mills coupling we
establish the existence of a third order phase transition where the theory
crosses over from the Yang-Mills phase to the Chern-Simons phase. The phase
transition exists for any value of , although the details differ
between small and large values of . For pure Chern-Simons
theories we present evidence for a chain of phase transitions as
is increased.
We also find the expectation values for supersymmetric circular Wilson loops
in these various scenarios and show that the Chern-Simons term leads to
different physical properties for fundamental and anti-fundamental Wilson
loops. Different choices of the integration contours also lead to different
properties for the loops.Comment: 40 pages, 17 figures, Minor corrections, Published versio
PT-symmetric interpretation of double-scaling
The conventional double-scaling limit of an O(N)-symmetric quartic quantum
field theory is inconsistent because the critical coupling constant is
negative. Thus, at the critical coupling the Lagrangian defines a quantum
theory with an upside-down potential whose energy appears to be unbounded
below. Worse yet, the integral representation of the partition function of the
theory does not exist. It is shown that one can avoid these difficulties if one
replaces the original theory by its PT-symmetric analog. For a zero-dimensional
O(N)-symmetric quartic vector model the partition function of the PT-symmetric
analog is calculated explicitly in the double-scaling limit.Comment: 11 pages, 2 figure
Improved Term of the Electron Anomalous Magnetic Moment
We report a new value of electron , or , from 891 Feynman diagrams
of order . The FORTRAN codes of 373 diagrams containing closed
electron loops have been verified by at least two independent formulations. For
the remaining 518 diagrams, which have no closed lepton loop, verification by a
second formulation is not yet attempted because of the enormous amount of
additional work required. However, these integrals have structures that allow
extensive cross-checking as well as detailed comparison with lower-order
diagrams through the renormalization procedure. No algebraic error has been
uncovered for them. The numerical evaluation of the entire term by
the integration routine VEGAS gives , where the
uncertainty is obtained by careful examination of error estimates by VEGAS.
This leads to ,
where the uncertainties come from the term, the estimated
uncertainty of term, and the inverse fine structure constant,
, measured by atom interferometry combined
with a frequency comb technique, respectively. The inverse fine structure
constant derived from the theory and the Seattle
measurement of is .Comment: 64 pages and 10 figures. Eq.(16) is corrected. Comments are added
after Eq.(40
A Minimization Method for Relativistic Electrons in a Mean-Field Approximation of Quantum Electrodynamics
We study a mean-field relativistic model which is able to describe both the
behavior of finitely many spin-1/2 particles like electrons and of the Dirac
sea which is self-consistently polarized in the presence of the real particles.
The model is derived from the QED Hamiltonian in Coulomb gauge neglecting the
photon field. All our results are non-perturbative and mathematically rigorous.Comment: 18 pages, 3 figure
Partition Functions for Maxwell Theory on the Five-torus and for the Fivebrane on S1XT5
We compute the partition function of five-dimensional abelian gauge theory on
a five-torus T5 with a general flat metric using the Dirac method of quantizing
with constraints. We compare this with the partition function of a single
fivebrane compactified on S1 times T5, which is obtained from the six-torus
calculation of Dolan and Nappi. The radius R1 of the circle S1 is set to the
dimensionful gauge coupling constant g^2= 4\pi^2 R1. We find the two partition
functions are equal only in the limit where R1 is small relative to T5, a limit
which removes the Kaluza-Klein modes from the 6d sum. This suggests the 6d
N=(2,0) tensor theory on a circle is an ultraviolet completion of the 5d gauge
theory, rather than an exact quantum equivalence.Comment: v4, 37 pages, published versio
Breit Hamiltonian and QED Effects for Spinless Particles
We describe a simplified derivation for the relativistic corrections of order
for a bound system consisting of two spinless particles. We devote
special attention to pionium, the bound system of two oppositely charged pions.
The leading quantum electrodynamic (QED) correction to the energy levels is of
the order of and due to electronic vacuum polarization. We analyze
further corrections due to the self-energy of the pions, and due to recoil
effects, and we give a complete result for the scalar-QED leading logarithmic
corrections which are due to virtual loops involving only the scalar
constituent particles (the pions); these corrections are of order for S states.Comment: 12 pages, LaTeX; references added (J. Phys. B, in press
First-principles calculations of the phonon dispersion curves of H on Pt(111)
We have calculated the surface phonon dispersion curves for H on Pt(111),
using first-principles, total energy calculations based on a mixed-basis set
and norm-conserving pseudopotentials. Linear response theory and the harmonic
approximation are invoked. For one monolayer of H in the preferred adsorption
site (fcc hollow) vibrational modes polarized parallel and perpendicular to the
surface are found, respectively, at 73.5 meV and 142.6 meV, at the Γ point
of the surface Brillouin zone. The degeneracy of the parallel mode is lifted at
the zone boundaries, yielding energies of 69.6 meV and 86.3 meV at the M point
and 79.4 meV and 80.8 meV at the K point. The dispersion curves for H
adsorption at the hcp hollow site differ only slightly from the above. In
either case, H adsorption has considerable impact on the substrate modes; in
particular the surface mode in the gap in the bulk phonon spectrum (around M
point) is pushed into the bulk band. For on-top H adsorption, modes polarized
parallel and perpendicular to the surface have respective energies of 47.4 meV
and 277.2 meV, at the Γ point. The former disperses to 49.1 meV and 59.5
meV at the M point and to 56 meV and 56.7 meV at the K point. The H vibrational
mode polarized perpendicular to the surface shows little dispersion, in all
three cases considered. Insights are obtained from the hybridization of the H
and Pt electronic states.Comment: 26 pages, 6 figure
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