205 research outputs found
Effective Field Theory of Gravity: Leading Quantum Gravitational Corrections to Newtons and Coulombs Law
In this paper we consider general relativity and its combination with scalar
quantum electrodynamics (QED) as an effective quantum field theory at energies
well below the Planck scale. This enables us to compute the one-loop quantum
corrections to the Newton and Coulomb potential induced by the combination of
graviton and photon fluctuations. We derive the relevant Feynman rules and
compute the nonanalytical contributions to the one-loop scattering matrix for
charged scalars in the nonrelativistic limit. In particular, we derive the
post-Newtonian corrections of order from general relativity
and the genuine quantum corrections of order .Comment: 14 pages, 12 figure
Production of relativistic positronium in collisions of photons and electrons with nuclei and atoms
We consider the production of ultrarelativistic positronium (Ps) in and processes where is an atom or a nucleus
with charge . For the photoproduction of para- and ortho-Ps and the
electroproduction of para-Ps we obtain the most complete description compared
with previous works. It includes high order corrections and
polarization effects. The accuracy of the obtained cross sections is determined
by omitted terms of the order of the inverse Ps Lorentz factor squared. The
studied high order multi-photon electroproduction of ortho-Ps dominates for the
collision of electrons with heavy atoms over the bremsstrahlung production from
the electron via a virtual photon proposed by Holvik and Olsen. Our results
complete and correct the studies of those authors.Comment: 19 pages, 9 figures, RevTex; v2: minor corrections for the accuracy
of the results, a discussion of the literature added in a footnote, one
additional reference; v3: diagram of Fig.2 correcte
Light-induced transmission nonlinearities in gallium selenide
The intensity of a He–Ne laser (633 nm, 5 mW) transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium–aluminum–garnet laser pulse (532 nm, 7.8 ns, 3 mJ) which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and [email protected] ; [email protected] ; [email protected] ; [email protected]
Production of para-- and orthopositronium at relativistic heavy ion colliders
We consider the ortho-- and parapositronium production in the process Ps where A is a nucleus with the charge number Z. The inclusive cross
section and the energy distribution of the relativistic Ps are calculated which
are of primary interest from the experimental point of view. The accuracy of
the corresponding cross sections is given by omitting terms for the para--Ps and for the ortho--Ps production
where and 16 for the RHIC and the LHC. Within this
accuracy the multiphoton (Coulomb) corrections are taken into account. We show
that the RHIC and the LHC will be Ps factories with a productions rate of about
relativistic Ps per day. The fraction of the ortho--Ps is
expected to be of the same order as that of the para--Ps for Au--Au and Pb--Pb
collisions.Comment: 22 pages, 5 figures, RevTeX, misprint correcte
The proton and deuteron F_2 structure function at low Q^2
Measurements of the proton and deuteron structure functions are
presented. The data, taken at Jefferson Lab Hall C, span the four-momentum
transfer range GeV, and Bjorken values from 0.009 to
0.45, thus extending the knowledge of to low values of at low .
Next-to-next-to-leading order calculations using recent parton distribution
functions start to deviate from the data for GeV at the low and
high -values. Down to the lowest value of , the structure function is
in good agreement with a parameterization of based on data that have been
taken at much higher values of or much lower values of , and which is
constrained by data at the photon point. The ratio of the deuteron and proton
structure functions at low remains well described by a logarithmic
dependence on at low .Comment: 3 figures, submitted pape
Measurement of the proton and deuteron structure functions, F2p and F2d, and of the ratio sigma(L)/sigma(T)
The muon-proton and muon-deuteron inclusive deep inelastic scattering cross
sections were measured in the kinematic range 0.002 < x < 0.60 and 0.5 < Q2 <
75 GeV2 at incident muon energies of 90, 120, 200 and 280 GeV. These results
are based on the full data set collected by the New Muon Collaboration,
including the data taken with a small angle trigger. The extracted values of
the structure functions F2p and F2d are in good agreement with those from other
experiments. The data cover a sufficient range of y to allow the determination
of the ratio of the longitudinally to transversely polarised virtual photon
absorption cross sections, R= sigma(L)/sigma(T), for 0.002 < x < 0.12 . The
values of R are compatible with a perturbative QCD prediction; they agree with
earlier measurements and extend to smaller x.Comment: In this replacement the erroneously quoted R values in tables 3-6 for
x>0.12, and R1990 values in tables 5-6 for all x, have been corrected, and
the cross sections in tables 3-4 have been adapted. Everything else,
including the structure functions F2, remained unchanged. 22 pages, LateX,
including figures, with two .sty files, and three separate f2tab.tex files
for the F2-tables. Accepted for publication in Nucl.Phys.B 199
Radiative Corrections to \zbb from Colored Scalars in a Model with Dynamical Symmetry Breaking
Isodoublet color-octet scalar bosons appear in the low-energy limit of a
natural extension of the Standard Model in which the electroweak symmetry is
broken by a condensate. We briefly discuss the model and show that
radiative corrections (involving these scalars) to the branching ratio
are
negative and thus place a stringent lower bound on the masses of the colored
scalars. This turns out to be GeV with GeV and increases
quadratically with . It is emphasized that is a parameter that is
well-determined experimentally and that theoretical estimates are relatively
free from uncertainties emanating from hadronic corrections and are
comparatively insensitive to the value of the top mass.Comment: 9 pages + 3 figures (available upon request), TeX file. Saha
Institute Preprint no. SINP-TNP/93-22 (December 1993
Quantum power correction to the Newton law
We have found the graviton contribution to the one-loop quantum correction to
the Newton law. This correction results in interaction decreasing with distance
as 1/r^3 and is dominated numerically by the graviton contribution. The
previous calculations of this contribution to the discussed effect are
demonstrated to be incorrect.Comment: 10 pages, 5 figures; numerical error corrected, few references adde
Universality-Breaking Effects in Leptonic Z Decays
We analyze the possibility of universality violation in diagonal leptonic
decays of the boson, in the context of interfamily "see-saw" models. In a
minimal extension of the Standard Model with right-handed neutrino fields, we
find that universality-breaking effects increase quadratically with the heavy
Majorana neutrino mass and may be observed in the running experiments.Comment: MZ-TH/93-04 #, LaTeX, 14 p. (2 Figs
Longitudinal-Transverse Separations of Structure Functions at Low for Hydrogen and Deuterium
We report on a study of the longitudinal to transverse cross section ratio,
, at low values of and , as determined from
inclusive inelastic electron-hydrogen and electron-deuterium scattering data
from Jefferson Lab Hall C spanning the four-momentum transfer range 0.06 GeV. Even at the lowest values of , remains
nearly constant and does not disappear with decreasing , as expected. We
find a nearly identical behaviour for hydrogen and deuterium.Comment: 4 pages, 2 gigure
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