7,347 research outputs found
From amplitudes to gravitational radiation with cubic interactions and tidal effects
We study the effect of cubic and tidal interactions on the spectrum of gravitational waves emitted in the inspiral phase of the merger of two nonspinning objects. There are two independent parity-even cubic interaction terms, which we take to be
I
1
=
R
α
β
μ
ν
R
μ
ν
ρ
σ
R
ρ
σ
α
β
and
G
3
=
I
1
−
2
R
α
μ
β
ν
R
μ
ρ
ν
σ
R
ρ
α
σ
β
. The latter has vanishing pure graviton amplitudes but modifies mixed scalar/graviton amplitudes which are crucial for our study. Working in an effective field theory setup, we compute the modifications to the quadrupole moment due to
I
1
,
G
3
and tidal interactions, from which we obtain the power of gravitational waves radiated in the process to first order in the perturbations and leading order in the post-Minkowskian expansion. The
I
1
predictions are novel, and we find that our results for
G
3
are related to the known quadrupole corrections arising from tidal perturbations, although the physical origin of the
G
3
coupling is unrelated to the finite-size effects underlying tidal interactions. We show this by recomputing such tidal corrections and by presenting an explicit field redefinition. In the post-Newtonian expansion our results are complete at leading order, which for the gravitational-wave flux is 5PN for
G
3
and tidal interactions and 6PN for
I
1
. Finally, we compute the corresponding modifications to the waveforms
Note on the absence of R-2 corrections to Newton's potential
We consider Einstein gravity with the addition of and interactions in the context of effective field theory, and the
corresponding scattering amplitudes of gravitons and minimally-coupled heavy
scalars. First, we recover the known fact that graviton amplitudes are the same
as in Einstein gravity. Then we show that all amplitudes with two heavy scalars
and an arbitrary number of gravitons are also not affected by these
interactions. We prove this by direct computations, using field redefinitions
known from earlier applications in string theory, and with a combination of
factorisation and power-counting arguments. Combined with unitarity, these
results imply that, in an effective field theory approach, the Newtonian
potential receives neither classical nor quantum corrections from terms
quadratic in the curvature.Comment: 15 page
Complete form factors in Yang-Mills from unitarity and spinor helicity in six dimensions
We present a systematic procedure to compute complete, analytic form factors
of gauge-invariant operators at loop level in pure Yang-Mills. We consider
applications to operators of the form where is the
gluon field strength. Our approach is based on an extension to form factors of
the dimensional reconstruction technique, in conjunction with the
six-dimensional spinor-helicity formalism and generalised unitarity. For form
factors this technique requires the introduction of additional scalar
operators, for which we provide a systematic prescription. We also discuss a
generalisation of dimensional reconstruction to any number of loops, both for
amplitudes and form factors. Several novel results for one-loop minimal and
non-minimal form factors of with are presented.
Finally, we describe the \texttt{Mathematica} package
\texttt{SpinorHelicity6D}, which is tailored to handle six-dimensional
quantities written in the spinor-helicity formalism.Comment: 56 page
Measure of genuine multipartite entanglement with computable lower bounds
We introduce an intuitive measure of genuine multipartite entanglement which
is based on the well-known concurrence. We show how lower bounds on this
measure can be derived that also meet important characteristics of an
entanglement measure. These lower bounds are experimentally implementable in a
feasible way enabling quantification of multipartite entanglement in a broad
variety of cases.Comment: 5 pages, 2 figure
Perturbing exactly tri-bimaximal neutrino mixings with charged lepton mass matrices
We study perturbations of exactly tri-bimaximal neutrino mixings under the
assumption that they are coming solely from the charged lepton mass matrix.
This may be plausible in scenarios where the mass generation mechanisms of
neutrinos and charged leptons/quarks have a different origin. As a working
hypothesis, we assume mass textures which may be generated by the
Froggatt-Nielsen mechanism for the charged lepton and quark sectors, which
generically leads to strong hierarchies, whereas the neutrino sector is exactly
tri-bimaximal with a mild (normal) hierarchy. We find that in this approach,
deviations from maximal atmospheric mixing can be introduced without affecting
theta_13 and theta_12, whereas a deviation of theta_13 or theta_12 from its
tri-bimaximal value will inevitably lead to a similar-sized deviation of the
other parameter. Therefore, the already very precise knowledge of theta_12
points towards small sin^2(2 theta_13) <= 0.01. The magnitude of this deviation
can be controlled by the specific form of the charged lepton texture.Comment: 13 pages, 9 figures; matches published version, changes in notatio
Atomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study
We study the atomic oxygen adsorption on Pb(111) surface by using
density-functional theory within the generalized gradient approximation and a
supercell approach. The atomic and energetic properties of purely on-surface
and subsurface oxygen structures at the Pb(111) surface are systematically
investigated for a wide range of coverages and adsorption sites. The fcc and
tetra-II sites (see the text for definition) are found to be energetically
preferred for the on-surface and subsurface adsorption, respectively, in the
whole range of coverage considered. The on-surface and subsurface oxygen
binding energies monotonically increase with the coverage, and the latter is
always higher than the former, thus indicating the tendency to the formation of
oxygen islands (clusters) and the higher stability of subsurface adsorption.
The on-surface and subsurface diffusion-path energetics of atomic oxygen, and
the activation barriers for the O penetration from the on-surface to the
subsurface sites are presented at low and high coverages. In particular, it is
shown that the penetration barrier from the on-surface hcp to the subsurface
tetra-I site is as small as 65 meV at low coverage (=0.25). The other
properties of the O/Pb(111) system, including the charge distribution, the
lattice relaxation, the work function, and the electronic density of states,
are also studied and discussed in detail, which consistently show the gradually
stabilizing ionic O-Pb bond with increase of the oxygen coverage.Comment: 31 pages, 16 figure
Majorana neutrinos with split fermions in extra dimensions
We propose new solutions to the neutrino mass problem in theories with large
extra dimensions in a thick wall scenario. It has recently been argued that our
3-brane could be a thick wall at the boundary of the bulk. The gauge bosons and
the Higgs scalars have an almost flat profile on this wall, while fermions
could have localized profile with left-handed and right-handed components
displaced with respect to each other. We point out that with split fermions it
is possible to generate Majorana neutrino masses contributing to the
neutrinoless double beta decay. The almost degenerate neutrinos can also come
out naturally in this case. Unlike other models of neutrino masses in extra
dimensions there are no bulk fields in this scenario.Comment: 12 pages, 1 figure, revise
Robust artificial neural networks and outlier detection. Technical report
Large outliers break down linear and nonlinear regression models. Robust
regression methods allow one to filter out the outliers when building a model.
By replacing the traditional least squares criterion with the least trimmed
squares criterion, in which half of data is treated as potential outliers, one
can fit accurate regression models to strongly contaminated data.
High-breakdown methods have become very well established in linear regression,
but have started being applied for non-linear regression only recently. In this
work, we examine the problem of fitting artificial neural networks to
contaminated data using least trimmed squares criterion. We introduce a
penalized least trimmed squares criterion which prevents unnecessary removal of
valid data. Training of ANNs leads to a challenging non-smooth global
optimization problem. We compare the efficiency of several derivative-free
optimization methods in solving it, and show that our approach identifies the
outliers correctly when ANNs are used for nonlinear regression
Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry
We compute the branching ratios for mu-> e gamma, tau-> mu gamma and tau -> e
gamma in a supersymmetric model invariant under the flavour symmetry group A4 X
Z3 X U(1)_{FN}, in which near tri-bimaximal lepton mixing is naturally
predicted. At leading order in the small symmetry breaking parameter u, which
is of the same order as the reactor mixing angle theta_{13}, we find that the
branching ratios generically scale as u^2. Applying the current bound on the
branching ratio of mu -> e gamma shows that small values of u or tan(beta) are
preferred in the model for mass parameters m_{SUSY} and m_{1/2} smaller than
1000 GeV. The bound expected from the on-going MEG experiment will provide a
severe constraint on the parameter space of the model either enforcing u approx
0.01 and small tan(beta) or m_{SUSY} and m_{1/2} above 1000 GeV. In the special
case of universal soft supersymmetry breaking terms in the flavon sector a
cancellation takes place in the amplitudes and the branching ratios scale as
u^4, allowing for smaller slepton masses. The branching ratios for tau -> mu
gamma and tau -> e gamma are predicted to be of the same order as the one for
mu -> e gamma, which precludes the possibility of observing these tau decays in
the near future.Comment: 44 page
Limits on the Non-Standard Interactions of Neutrinos from Colliders
We provide an effective Lagrangian analysis of contact non-standard
interactions of neutrinos with electrons, which can be effectively mediated by
extra particles, and examine the associated experimental limits. At present,
such interactions are strongly constrained only for : the bounds are
loose for and absent for . We emphasize the unique role
played by the reaction in providing direct
constraints on such non-standard interactions.Comment: 15 LaTeX pages, 6 postscript figures, uses epsfig. New discussion on
bounds from reactor anti-neutrino scattering off electrons; minor changes. To
appear on Phys. Lett.
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