9,910 research outputs found
Symmetries, Horizons, and Black Hole Entropy
Black holes behave as thermodynamic systems, and a central task of any
quantum theory of gravity is to explain these thermal properties. A statistical
mechanical description of black hole entropy once seemed remote, but today we
suffer an embarrassment of riches: despite counting very different states, many
inequivalent approaches to quantum gravity obtain identical results. Such
``universality'' may reflect an underlying two-dimensional conformal symmetry
near the horizon, which can be powerful enough to control the thermal
characteristics independent of other details of the theory. This picture
suggests an elegant description of the relevant degrees of freedom as
Goldstone-boson-like excitations arising from symmetry breaking by the
conformal anomaly.Comment: 6 pages; first prize essay, 2007 Gravity Research Foundation essay
contes
Ten easy steps to conducting transparent, reproducible meta‐analyses for infant researchers
Meta-analyses provide researchers with an overview of the body of evidence in a topic, with quantified estimates of effect sizes and the role of moderators, and weighting studies according to their precision. We provide a guide for conducting a transparent and reproducible meta-analysis in the field of developmental psychology within the framework of the MetaLab platform, in 10 steps: (1) Choose a topic for your meta-analysis, (2) Formulate your research question and specify inclusion criteria, (3) Preregister and document all stages of your meta-analysis, (4) Conduct the literature search, (5) Collect and screen records, (6) Extract data from eligible studies, (7) Read the data into analysis software and compute effect sizes, (8) Visualize your data, (9) Create meta-analytic models to assess the strength of the effect and investigate possible moderators, (10) Write up and promote your meta-analysis. Meta-analyses can inform future studies, through power calculations, by identifying robust methods and exposing research gaps. By adding a new meta-analysis to MetaLab, datasets across multiple topics of developmental psychology can be synthesized, and the dataset can be maintained as a living, community-augmented meta-analysis to which researchers add new data, allowing for a cumulative approach to evidence synthesis
Lepton number violating interactions and their effects on neutrino oscillation experiments
Mixing between bosons that transform differently under the standard model
gauge group, but identically under its unbroken subgroup, can induce
interactions that violate the total lepton number. We discuss four-fermion
operators that mediate lepton number violating neutrino interactions both in a
model-independent framework and within supersymmetry (SUSY) without R-parity.
The effective couplings of such operators are constrained by: i) the upper
bounds on the relevant elementary couplings between the bosons and the
fermions, ii) by the limit on universality violation in pion decays, iii) by
the data on neutrinoless double beta decay and, iv) by loop-induced neutrino
masses. We find that the present bounds imply that lepton number violating
neutrino interactions are not relevant for the solar and atmospheric neutrino
problems. Within SUSY without R-parity also the LSND anomaly cannot be
explained by such interactions, but one cannot rule out an effect
model-independently. Possible consequences for future terrestrial neutrino
oscillation experiments and for neutrinos from a supernova are discussed.Comment: 28 pages, 2 figures, Late
Effects of new physics in neutrino oscillations in matter
A new flavor changing electron neutrino interaction with matter would always
dominate the nu_e oscillation probability at sufficiently high neutrino
energies. Being suppressed by theta_{13}, the energy scale at which the new
effect starts to be relevant may be within the reach of realistic experiments,
where the peculiar dependence of the signal with energy could give rise to a
clear signature in the nu_e --> nu_tau channel. The latter could be observed by
means of a coarse large magnetized detector by exploiting tau --> mu decays. We
discuss the possibility of identifying or constraining such effects with a high
energy neutrino factory. We also comment on the model independent limits on
them.Comment: 11 pages, 5 figure
Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias
A standard drift-diffusion model of space charge wave propagation in
semiconductors has been studied numerically and analytically under dc voltage
bias. For sufficiently long samples, appropriate contact resistivity and
applied voltage - such that the sample is biased in a regime of negative
differential resistance - we find chaos in the propagation of nonlinear fronts
(charge monopoles of alternating sign) of electric field. The chaos is always
low-dimensional, but has a complex spatial structure; this behavior can be
interpreted using a finite dimensional asymptotic model in which the front
(charge monopole) positions and the electrical current are the only dynamical
variables.Comment: 12 pages, 8 figure
The muonic longitudinal shower profiles at production
In this paper the longitudinal profile of muon production along the shower
axis is studied. The characteristics of this distribution is investigated for
different primary masses, zenith angles, primary energies, and different high
energy hadronic models. It is found that the shape of this distribution
displays universal features similarly to what is known for the electromagnetic
profile. The relation between the muon production distribution and the
longitudinal electromagnetic evolution is also discussed
Zeeman effect of the hyperfine structure levels in hydrogenlike ions
The fully relativistic theory of the Zeeman splitting of the hyperfine
structure levels in hydrogenlike ions is considered for the magnetic field
magnitude in the range from 1 to 10 T. The second-order corrections to the
Breit -- Rabi formula are calculated and discussed. The results can be used for
a precise determination of nuclear magnetic moments from factor
experiments.Comment: 13 page
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