15,465 research outputs found
On the Speed of Gravity and the Corrections to the Shapiro Time Delay
Using a relatively simple method, I compute the v/c correction to the
gravitational time delay for light passing by a massive object moving with
speed v. It turns out that the v/c effects are too small to have been measured
in the recent experiment involving Jupiter and quasar J0842+1845 that was used
to measure the speed of gravity.Comment: 8 pages, LaTeX (or Latex, etc), one figure, which is also available
at http://www-theory.lbl.gov/~samuel/sog_figure.pdf; Revised version is the
one to appear in Phys. Rev. Lett
Perturbatively Defined Effective Classical Potential in Curved Space
The partition function of a quantum statistical system in flat space can
always be written as an integral over a classical Boltzmann factor \exp[
-\beta V^{\rm eff cl({\bf x}_0)], where V^{\rm eff cl({\bf x}_0) is the
so-called effective classical potential containing the effects of all quantum
fluctuations. The variable of integration is the temporal path average {\bf
x_0\equiv \beta ^{-1}\int_0^ \beta d\tau {\bf x}(\tau). We show how to
generalize this concept to paths in curved space with metric
g_{\mu \nu (q), and calculate perturbatively the high-temperature expansion
of V^{\rm eff cl(q_0). The requirement of independence under coordinate
transformations introduces subtleties in the
definition and treatment of the path average , and covariance is
achieved only with the help of a suitable Faddeev-Popov procedure.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/33
On the power counting of loop diagrams in general relativity
A class of loop diagrams in general relativity appears to have a behavior
which would upset the utility of the energy expansion for quantum effects. We
show through the study of specific diagrams that cancellations occur which
restore the expected behaviour of the energy expansion. By considering the
power counting in a physical gauge we show that the apparent bad behavior is a
gauge artifact, and that the quantum loops enter with a well behaved energy
expansion.Comment: 29 pages, uses axodraw and epsfig.tex, one small .eps file is
included. The full PostScript version is also available as
http://het.phast.umass.edu/students/kakukk/powercount_hepth.p
Bi-partite entanglement entropy in massive two-dimensional quantum field theory
Recently, Cardy, Castro Alvaredo and the author obtained the first
exponential correction to saturation of the bi-partite entanglement entropy at
large region length, in massive two-dimensional integrable quantum field
theory. It only depends on the particle content of the model, and not on the
way particles scatter. Based on general analyticity arguments for form factors,
we propose that this result is universal, and holds for any massive
two-dimensional model (also out of integrability). We suggest a link of this
result with counting pair creations far in the past.Comment: 5 pages, 2 figures. v2: improved presentation of result and
calculations, section "discussion" adjusted, references adjuste
What is the Discrete Gauge Symmetry of the MSSM?
We systematically study the extension of the Supersymmetric Standard Model
(SSM) by an anomaly-free discrete gauge symmetry Z_N. We extend the work of
Ibanez and Ross with N=2,3 to arbitrary values of N. As new fundamental
symmetries, we find four Z_6, nine Z_9 and nine Z_18. We then place three
phenomenological demands upon the low-energy effective SSM: (i) the presence of
the mu-term in the superpotential, (ii) baryon-number conservation upto
dimension-five operators, and (iii) the presence of the see-saw neutrino mass
term LHLH. We are then left with only two anomaly-free discrete gauge
symmetries: baryon-triality, B_3, and a new Z_6, which we call proton-hexality,
P_6. Unlike B_3, P_6 prohibits the dimension-four lepton-number violating
operators. This we propose as the discrete gauge symmetry of the Minimal SSM,
instead of R-parity.Comment: Typo in item 2 below Eq.(6.9) corrected (wrong factor of "3"); 27
pages, 5 table
Adiabatic Modes in Cosmology
We show that the field equations for cosmological perturbations in Newtonian
gauge always have an adiabatic solution, for which a quantity is
non-zero and constant in all eras in the limit of large wavelength, so that it
can be used to connect observed cosmological fluctuations in this mode with
those at very early times. There is also a second adiabatic mode, for which
vanishes for large wavelength, and in general there may be
non-adiabatic modes as well. These conclusions apply in all eras and whatever
the constituents of the universe, under only a mild technical assumption about
the wavelength dependence of the field equations for large wave length. In the
absence of anisotropic inertia, the perturbations in the adiabatic modes are
given for large wavelength by universal formulas in terms of the
Robertson--Walker scale factor. We discuss an apparent discrepancy between
these results and what appears to be a conservation law in all modes found for
large wavelength in synchronous gauge: it turns out that, although equivalent,
synchronous and Newtonian gauges suggest inequivalent assumptions about the
behavior of the perturbations for large wavelength.Comment: 24 pages, Latex, no special macro
Chemisorption on a model bcc metal
The system considered here is that of a single atom with one energy level chemisorbed on the (001) surface of a model bcc metal. We present the change in the density of electronic states Δn (E) due to chemisorption for two cases: one when the adatom is bound to a single substrate atom in the "on‐site" configuration and the other when it is bound to four substrate atoms in the "centered fourfold site." In principle, this change in the density of states Δn can be related to the results of photoemission measurements
Einstein-Podolsky-Rosen correlations in a hybrid system
We calculate the relativistic correlation function for a hybrid system of a
photon and a Dirac-particle. Such a system can be produced in decay of another
spin-1/2 fermion. We show, that the relativistic correlation function, which
depends on particle momenta, may have local extrema for fermion velocity of
order 0.5 c. This influences the degree of violation of CHSH inequality.Comment: 9 pages, 6 figure
Tetrads in Geometrodynamics
A new tetrad is introduced within the framework of geometrodynamics for
non-null electromagnetic fields. This tetrad diagonalizes the electromagnetic
stress-energy tensor and allows for maximum simplification of the expression of
the electromagnetic field. The Einstein-Maxwell equations will also be
simplified
Dressing the electromagnetic nucleon current
A field-theory-based approach to pion photoproduction off the nucleon is used
to derive a microscopically consistent formulation of the fully dressed
electromagnetic nucleon current in an effective Lagrangian formalism. It is
shown how the rigorous implementation of local gauge invariance at all levels
of the reaction dynamics provides equations that lend themselves to practically
manageable truncations of the underlying nonlinearities of the problem. The
requirement of consistency also suggests a novel way of treating the pion
photoproduction problem. Guided by a phenomenological implementation of gauge
invariance for the truncated equations that has proved successful for pion
photoproduction, an expression for the fully dressed nucleon current is given
that satisfies the Ward-Takahashi identity for a fully dressed nucleon
propagator as a matter of course. Possible applications include meson photo-
and electroproduction processes, bremsstrahlung, Compton scattering, and
processes off nucleons.Comment: 10 pages, 9 figure
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