1,556 research outputs found
Proposal for an experiment to search for Randall-Sundrum type corrections to Newton's law of gravitation
String theory, as well as the string inspired brane-world models such as the
Randall-Sundrum (RS) one, suggest a modification of Newton's law of gravitation
at small distance scales. Search for modifications of standard gravity is an
active field of research in this context. It is well known that short range
corrections to gravity would violate the Newton-Birkhoff theorem. Based on
calculations of RS type non-Newtonian forces for finite size spherical bodies,
we propose a torsion balance based experiment to search for the effects of
violation of this celebrated theorem valid in Newtonian gravity as well as the
general theory of relativity. We explain the main principle behind the
experiment and provide detailed calculations suggesting optimum values of the
parameters of the experiment. The projected sensitivity is sufficient to probe
the Randall-Sundrum parameter up to 10 microns.Comment: 4 pages and 5 figures, figures improved, minor clarifications and few
references added, final version to appear in PRD (rapid communications
Evidence for Solar Influences on Nuclear Decay Rates
Recent reports of periodic fluctuations in nuclear decay data of certain
isotopes have led to the suggestion that nuclear decay rates are being
influenced by the Sun, perhaps via neutrinos. Here we present evidence for the
existence of an additional periodicity that appears to be related to the Rieger
periodicity well known in solar physics.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
K-Chameleon and the Coincidence Problem
In this paper we present a hybrid model of k-essence and chameleon, named as
k-chameleon. In this model, due to the chameleon mechanism, the directly strong
coupling between the k-chameleon field and matters (cold dark matters and
baryons) is allowed. In the radiation dominated epoch, the interaction between
the k-chameleon field and background matters can be neglected, the behavior of
the k-chameleon therefore is the same as that of the ordinary k-essence. After
the onset of matter domination, the strong coupling between the k-chameleon and
matters dramatically changes the result of the ordinary k-essence. We find that
during the matter-dominated epoch, only two kinds of attractors may exist: one
is the familiar {\bf K} attractor and the other is a completely {\em new},
dubbed {\bf C} attractor. Once the universe is attracted into the {\bf C}
attractor, the fraction energy densities of the k-chameleon and
dust matter are fixed and comparable, and the universe will undergo
a power-law accelerated expansion. One can adjust the model so that the {\bf K}
attractor do not appear. Thus, the k-chameleon model provides a natural
solution to the cosmological coincidence problem.Comment: Revtex, 17 pages; v2: 18 pages, two figures, more comments and
references added, to appear in PRD, v3: published versio
Galaxy clustering constraints on deviations from Newtonian gravity at cosmological scales II: Perturbative and numerical analyses of power spectrum and bispectrum
We explore observational constraints on possible deviations from Newtonian
gravity by means of large-scale clustering of galaxies. We measure the power
spectrum and the bispectrum of Sloan Digital Sky Survey galaxies and compare
the result with predictions in an empirical model of modified gravity. Our
model assumes an additional Yukawa-like term with two parameters that
characterize the amplitude and the length scale of the modified gravity. The
model predictions are calculated using two methods; the second-order
perturbation theory and direct N-body simulations. These methods allow us to
study non-linear evolution of large-scale structure. Using the simulation
results, we find that perturbation theory provides reliable estimates for the
power spectrum and the bispectrum in the modified Newtonian model. We also
construct mock galaxy catalogues from the simulations, and derive constraints
on the amplitude and the length scale of deviations from Newtonian gravity. The
resulting constraints from power spectrum are consistent with those obtained in
our earlier work, indicating the validity of the previous empirical modeling of
gravitational nonlinearity in the modified Newtonian model. If linear biasing
is adopted, the bispectrum of the SDSS galaxies yields constraints very similar
to those from the power spectrum. If we allow for the nonlinear biasing
instead, we find that the ratio of the quadratic to linear biasing
coefficients, b_2/b_1, should satisfy -0.4 < b_2/b_1<0.3 in the modified
Newtonian model.Comment: 12 pages, 7 figure
Probing long-range leptonic forces with solar and reactor neutrinos
In this work we study the phenomenological consequences of the existence of
long-range forces coupled to lepton flavour numbers in solar neutrino
oscillations. We study electronic forces mediated by scalar, vector or tensor
neutral bosons and analyze their effect on the propagation of solar neutrinos
as a function of the force strength and range. Under the assumption of one mass
scale dominance, we perform a global analysis of solar and KamLAND neutrino
data which depends on the two standard oscillation parameters, \Delta m^2_{21}
and \tan^2\theta_{12}, the force coupling constant, its range and, for the case
of scalar-mediated interactions, on the neutrino mass scale as well. We find
that, generically, the inclusion of the new interaction does not lead to a very
statistically significant improvement on the description of the data in the
most favored MSW LMA (or LMA-I) region. It does, however, substantially improve
the fit in the high-\Delta m^2 LMA (or LMA-II) region which can be allowed for
vector and scalar lepto-forces (in this last case if neutrinos are very
hierarchical) at 2.5\sigma. Conversely, the analysis allows us to place
stringent constraints on the strength versus range of the leptonic interaction.Comment: 20 pages, 8 figure
Impact of phonons on dephasing of individual excitons in deterministic quantum dot microlenses
Optimized light-matter coupling in semiconductor nanostructures is a key to
understand their optical properties and can be enabled by advanced fabrication
techniques. Using in-situ electron beam lithography combined with a
low-temperature cathodoluminescence imaging, we deterministically fabricate
microlenses above selected InAs quantum dots (QDs) achieving their efficient
coupling to the external light field. This enables to perform four-wave mixing
micro-spectroscopy of single QD excitons, revealing the exciton population and
coherence dynamics. We infer the temperature dependence of the dephasing in
order to address the impact of phonons on the decoherence of confined excitons.
The loss of the coherence over the first picoseconds is associated with the
emission of a phonon wave packet, also governing the phonon background in
photoluminescence (PL) spectra. Using theory based on the independent boson
model, we consistently explain the initial coherence decay, the zero-phonon
line fraction, and the lineshape of the phonon-assisted PL using realistic
quantum dot geometries
Testing the Dirac equation
The dynamical equations which are basic for the description of the dynamics
of quantum felds in arbitrary space--time geometries, can be derived from the
requirements of a unique deterministic evolution of the quantum fields, the
superposition principle, a finite propagation speed, and probability
conservation. We suggest and describe observations and experiments which are
able to test the unique deterministic evolution and analyze given experimental
data from which restrictions of anomalous terms violating this basic principle
can be concluded. One important point is, that such anomalous terms are
predicted from loop gravity as well as from string theories. Most accurate data
can be obtained from future astrophysical observations. Also, laboratory tests
like spectroscopy give constraints on the anomalous terms.Comment: 11 pages. to appear in: C. L\"ammerzahl, C.W.F. Everitt, and F.W.
Hehl (eds.): Gyros, Clocks, Interferometers...: Testing Relativistic Gravity
in Space, Lecture Notes in Physics 562, Springer 200
The Scattering Approach to the Casimir Force
We present the scattering approach which is nowadays the best tool for
describing the Casimir force in realistic experimental configurations. After
reminders on the simple geometries of 1d space and specular scatterers in 3d
space, we discuss the case of stationary arbitrarily shaped mirrors in
electromagnetic vacuum. We then review specific calculations based on the
scattering approach, dealing for example with the forces or torques between
nanostructured surfaces and with the force between a plane and a sphere. In
these various cases, we account for the material dependence of the forces, and
show that the geometry dependence goes beyond the trivial {\it Proximity Force
Approximation} often used for discussing experiments.Comment: Proceedings of the QFEXT'09 conference (Oklahoma, 2009
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