5,165 research outputs found
New probe of gravity: strongly lensed gravitational wave multi-messenger approach
Strong gravitational lensing by galaxies provides us with a unique
opportunity to understand the nature of gravity on galactic and extra-galactic
scales. In this paper, we propose a new multimessenger approach using data from
both gravitational wave (GW) and the corresponding electromagnetic (EM)
counterpart to infer the constraint of the modified gravity (MG) theory denoted
by the scale dependent phenomenological parameter. To demonstrate the
robustness of this approach, we calculate the time-delay predictions by
choosing various values of the phenomenological parameters and then compare
them with that from the general relativity (GR). For the third generation
ground-based GW observatory, with one typical strongly lensed GW+EM event, and
assuming that the dominated error from the stellar velocity dispersions is 5\%,
the GW time-delay data can distinguish an 18\% MG effect on a scale of tens of
kiloparsecs with a confidence level. Assuming GR and a Singular
Isothermal Sphere mass model, there exists a simplified consistency
relationship between time-delay and imaging data. This relationship does not
require for the velocity dispersion measurement, and hence can avoid major
uncertainties. By using this relationship, the multimessenger approach is able
to distinguish an MG effect. Our results show that the GW multimessenger
approach can play an important role in revealing the nature of gravity on the
galactic and extra-galactic scales.Comment: references update
Influence of electric fields on absorption spectra of AAB-stacked trilayer graphene
The band structures and optical properties of AAB-stacked trilayer graphenes
(AAB-TLG) are calculated by the tight-binding model and gradient approximation.
Three pairs of the energy bands exhibit very different energy dispersions at
low energy and saddle points at the middle energy. At zero electric field,
excitation channels exist in both the low and middle frequencies, and
cause the very rich joint density of states (JDOS). However, the structures in
the JDOS do not appear in the absorption spectra completely. Due to the
different contributions from the velocity metric elements, some excitation
transitions disappear in the spectra. Furthermore, the frequency and the
existence of the absorption structures are affected by the increase of the
electric field from zero.Comment: arXiv admin note: substantial text overlap with arXiv:1503.07958 by
other author
Testing the QCD fragmentation mechanism on heavy quarkonium production at LHC
We calculate the fragmentation function for charm quark into J/psi at the QCD
next-to-leading-order (NLO) and find that the produced J/psi is of larger
momentum fraction than it is at the leading-order. Based on the fragmentation
function and partonic processes calculated at the NLO, the transverse momentum
distribution on J/psi hadroproduction associated with a charm c (or \bar{c})
jet are predicted. We find that the distribution is enhanced by a factor of
2.0--3.3 at the NLO as p_t increased from 10 GeV to 100 GeV and it is
measurable at the LHC with charm tagger. The measurement at the LHC will supply
a first chance to directly test the QCD fragmentation mechanism on heavy
quarkonium production where the fragmentation function is calculable in
perturbative QCD. It is also applied to J/psi (Upsilon) production in the decay
of Z^0 (top quark).Comment: 4 pages, 3 figure
Deep Connection Between Thermodynamics and Gravity in Gauss-Bonnet Braneworld
We disclose the deep connection between the thermodynamics and gravity in a
general braneworld model with curvature correction terms on the brane and in
the bulk, respectively. We show that the Friedmann equations on the 3-brane
embedded in the 5D spacetime with curvature correction terms can be written
directly in the form of the first law of thermodynamics on the apparent
horizon. Using the first law, we extract the entropy expression of the apparent
horizon on the brane, which is useful in studying the thermodynamical
properties of the black hole horizon on the brane in Gauss-Bonnet gravity.Comment: 5 pages, revised version, accepted for publication in Phys. Rev.
CHAM: a fast algorithm of modelling non-linear matter power spectrum in the sCreened HAlo Model
We present a fast numerical screened halo model algorithm (CHAM) for modeling
non-linear power spectrum for the alternative models to LCDM. This method has
three obvious advantages. First of all, it is not being restricted to a
specific dark energy/modified gravity model. In principle, all of the screened
scalar-tensor theories can be applied. Second, the least assumptions are made
in the calculation. Hence, the physical picture is very easily understandable.
Third, it is very predictable and does not rely on the calibration from N-body
simulation. As an example, we show the case of Hu-Sawicki f(R) gravity. In this
case, the typical CPU time with the current parallel Python script (8 threads)
is roughly within minutes. The resulting spectra are in a good agreement
with N-body data within a few percentage accuracy up to k~1 h/Mpc.Comment: Python script is publicly available at
https://github.com/hubinitp/CHA
Entropy Perturbations in N-flation
In this paper we study the entropy perturbations in N-flation by using the
\d\ma{N} formalism. We calculate the entropy corrections to the power
spectrum of the overall curvature perturbation P_{\z}. We obtain an analytic
form of the transfer coefficient T^2_{\ma{R}\ma{S}}, which describes the
correlation between the curvature and entropy perturbations, and investigate
its behavior numerically. It turns out that the entropy perturbations cannot be
neglected in N-flation, because the amplitude of entropy components is
approximately in the same order as the adiabatic one at the end of inflation
T^2_{\ma{R}\ma{S}}\sim\ma{O}(1). The spectral index is calculated and
it becomes smaller after the entropy modes are taken into account, i.e., the
spectrum becomes redder, compared to the pure adiabatic case. Finally we study
the modified consistency relation of N-flation, and find that the
tensor-to-scalar ratio () is greatly suppressed by the entropy
modes, compared to the pure adiabatic one () at the end of
inflation.Comment: References added, some typos corrected and figures adjusted. Accepted
by Phys. Rev.
Scalar graviton in the healthy extension of Ho\v{r}ava-Lifshitz theory
In this note we study the linear dynamics of scalar graviton in a de Sitter
background in the infrared limit of the healthy extension of
Ho\v{r}ava-Lifshitz gravity with the dynamical critical exponent . Both
our analytical and numerical results show that the non-zero Fourier modes of
scalar graviton oscillate with an exponentially damping amplitude on the
sub-horizon scale, while on the super-horizon scale, the phases are frozen and
they approach to some asymptotic values. In addition, as the case of the
non-zero modes on super-horizon scale, the zero mode also initially decays
exponentially and then approaches to an asymptotic constant value.Comment: 12 pages, 1 figure, ghost free condition addressed, accepted by Phys.
Rev.
Acoustic signatures in the Cosmic Microwave Background bispectrum from primordial magnetic fields
Using the full radiation transfer function, we numerically calculate the CMB
angular bispectrum seeded by the compensated magnetic scalar density mode. We
find that, for the string inspired primordial magnetic fields characterized by
index and mean-field amplitude B_{\lam}=9{\rm nG}, the angular
bispectrum is dominated by two primordial magnetic shapes. The first magnetic
shape looks similar to the one from local-type primordial curvature
perturbations, so both the amplitude and profile of the Komatsu-Spergel
estimator (reduced bispectrum) seeded by this shape are almost the same as
those of the primary CMB anisotropies. However, for different parameter sets
(), this "local-type" reduced bispectrum oscillates around different
asymptotic values in the high- regime because of the effect of the Lorentz
force, which is exerted by the primordial magnetic fields on the charged
baryons. This feature is different from the standard case where all modes
approach to zero asymptotically in the high- limit. On the other hand, the
second magnetic shape appears only in the primordial magnetic field model. The
amplitude of the Komatsu-Spergel estimator sourced by the second shape diverges
in the low- regime because of the negative slope of shape. In the high-
regime, this amplitude is approximately equal to that of the first estimator,
but with a reversal phase.Comment: 37 pages, 11 figures, version published in JHE
Electron and hole lifetime in monolayer graphene
Excited conduction electrons, conduction holes, and valence holes in
monolayer electron-doped graphene exhibit unusual Coulomb decay rates. The
deexcitation processes are studied using the screened exchange energy. They
might utilize the intraband single-particle excitations (SPEs), the interband
SPEs, and the plasmon modes, depending on the quasiparticle states and the
Fermi energies. The low-lying valence holes can decay through the undamped
acoustic plasmon, so that they present very fast Coulomb deexcitations,
nonmonotonous energy dependence, and anisotropic behavior. However, the
low-energy conduction electrons and holes are similar to those in a
two-dimensional electron gas. The higher-energy conduction states and the
deeper-energy valence ones behave similarly in the available deexcitation
channels and have a similar dependence of decay rate on the wave vector
Characterization of microscopic deformation through two-point spatial correlation function
The molecular rearrangements of most fluids under flow and deformation do not
directly follow the macroscopic strain field. In this work, we describe a
phenomenological method for characterizing such non-affine deformation via the
anisotropic pair distribution function (PDF). We demonstrate now the
microscopic strain can be calculated in both simple shear and uniaxial
extension, by perturbation expansion of anisotropic PDF in terms of real
spherical harmonics. Our results, given in the real as well as the reciprocal
space, can be applied in spectrum analysis of small-angle scattering
experiments and non-equilibrium molecular dynamics simulations of soft matter
under flow
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