39 research outputs found
Quantum Gravitational Corrections to the Nonrelativistic Scattering Potential of Two Masses
We treat general relativity as an effective field theory, obtaining the full
nonanalytic component of the scattering matrix potential to one-loop order. The
lowest order vertex rules for the resulting effective field theory are
presented and the one-loop diagrams which yield the leading nonrelativistic
post-Newtonian and quantum corrections to the gravitational scattering
amplitude to second order in G are calculated in detail. The Fourier
transformed amplitudes yield a nonrelativistic potential and our result is
discussed in relation to previous calculations. The definition of a potential
is discussed as well and we show how the ambiguity of the potential under
coordinate changes is resolved.Comment: 27 pages, 17 figure
Vector-meson contributions do not explain the rate and spectrum in K_L -> pi0 gamma gamma
We analyze the recent NA48 data for the reaction K_L -> pi0 gamma gamma with
and without the assumption of vector meson dominance (VMD). We find that the
data is well described by a three-parameter expression inspired by O(p^6)
chiral perturbation theory. We also find that it is impossible to fit the shape
of the decay distribution and the overall rate simultaneously if one imposes
the VMD constraints on the three parameters. We comment on the different fits
and their implications for the CP-conserving component of the decay K_L -> pi0
e+ e-.Comment: Version accepted for publication on Phys. Rev. D. 19 pages, LaTeX, 8
figures, uses epsf.st
Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-
The long-distance contribution via the two-photon intermediate state to the
forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been
studied within the standard model. In order to evaluate the dispersive part of
the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a
phenomenological form factor to soften the ultraviolet behavior of the
transition. It is found that, this long-distance transition, although subject
to some theoretical uncertainties, can lead to significant contributions to the
forward-backward asymmetries, which could be tested in the future high-precise
experiments.Comment: 13 pages, 5 figure
Non-minimal kinetic coupling and Chaplygin gas cosmology
In the frame of the scalar field model with non minimal kinetic coupling to
gravity, we study the cosmological solutions of the Chaplygin gas model of dark
energy. By appropriately restricting the potential, we found the scalar field,
the potential and coupling giving rise to the Chaplygin gas solution.
Extensions to the generalized and modified Chaplygin gas have been made.Comment: 18 pages, 2 figures. To appear in EPJ
Performance of prototypes for the ALICE electromagnetic calorimeter
The performance of prototypes for the ALICE electromagnetic sampling
calorimeter has been studied in test beam measurements at FNAL and CERN. A
array of final design modules showed an energy resolution of about
11% / 1.7 % with a uniformity of the response
to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV.
The electromagnetic shower position resolution was found to be described by 1.5
mm 5.3 mm /. For an electron identification
efficiency of 90% a hadron rejection factor of was obtained.Comment: 10 pages, 10 figure
MO analysis of the high statistics Belle results on with chiral constraints
We reconsider Muskhelishvili-Omn\`es (MO) dispersive representations of
photon-photon scattering to two pions, motivated by the very high statistics
results recently released by the Belle collaboration for charged as well as
neutral pion pairs and also by recent progress in the determination of the
low-energy scattering amplitude. Applicability of this formalism is
extended beyond 1 GeV by taking into account inelasticity due to . A
modified MO representation is derived which has the advantage that all
polynomial ambiguities are collected into the subtraction constants and have
simple relations to pion polarizabilities. It is obtained by treating
differently the exactly known QED Born term and the other components of the
left-hand cut. These components are approximated by a sum over resonances. All
resonances up to spin two and masses up to GeV are included. The
tensor contributions to the left-hand cut are found to be numerically
important. We perform fits to the data imposing chiral constraints, in
particular, using a model independent sum rule result on the chiral
coupling . Such theoretical constraints are necessary because the
experimental errors are dominantly systematic. Results on further
couplings and pion dipole and quadrupole polarizabilities are then derived from
the fit. The relevance of the new data for distinguishing between two possible
scenarios of isospin breaking in the region is discussed.Comment: 44 pages, 12 figure
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
Asymptotically Safe Gravitons in Electroweak Precision Physics
Asymptotic safety offers a field theory based UV completion to gravity. For
low Planck scales, gravitational effects on low-energy precision observables
cannot be neglected. We compute the contribution to the rho parameter from
asymptotically safe gravitons and find that in contrast to effective theory,
constraints on models with more than three extra dimensions are significantly
weakened. The relative size of the trans-Planckian contribution increases
proportional to the number of extra dimensions.Comment: Published version; added references and additional minor changes
including appendi
Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
A41 Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
In: Addiction Science & Clinical Practice 2017, 12(Suppl 1): A4