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 $68\%$ 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 $8\%$ 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, $3$$^2$ 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 $10$ 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 $n_S$ 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 ($r\simeq0.006$) is greatly suppressed by the entropy modes, compared to the pure adiabatic one ($r\simeq0.017$) 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 $z=3$. 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 $n_B=-2.9$ 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 ($l_1,l_2$), this "local-type" reduced bispectrum oscillates around different asymptotic values in the high-$l_3$ 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-$l$ 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-$l$ regime because of the negative slope of shape. In the high-$l$ 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 ${\bf k}$

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