A Decisive test to confirm or rule out the existence of dark matter emulators using gravitational wave observations

We consider stable modified theories of gravity that reproduce galactic rotation curves and the observed amount of weak lensing without dark matter. In any such model gravity waves follow a different geodesic from that of other massless particles. For a specific class of models which we call "dark matter emulators," over cosmological distances this results in an easily detectable and difference between the arrival times of the pulse of gravity waves from some cosmic event and those of photons or neutrinos. For a repeat of SN 1987a (which took place in the Large Magellanic Cloud) the time lag is in the range of days. For the recent gamma ray burst, GRB 070201 (which seems to have taken place on the edge of the Andromeda galaxy) the time lag would be in the range of about two years.Comment: 4 Pages, no figures, Contributed to 12th Annual Gravitational Wave Data Analysis Workshop (GWDAW-12 2007): Connecting Gravitational Waves with Observational Astrophysics, Cambridge, Massachusetts, 13-16 Dec 200

The universe dominated by the extended Chaplygin gas

In this paper, we consider a universe dominated by the extended Chaplygin gas which recently proposed as the last version of Chaplygin gas models. Here, we only consider the second order term which recovers quadratic barotropic fluid equation of state. The density perturbations analyzed in both relativistic and Newtonian regimes and show that the model is stable without any phase transition and critical point. We confirmed stability of the model using thermodynamics point of view.Comment: 17 pages. Accepted in MPL

A useful guide for gravitational wave observers to test modified gravity models

We present an extension of a previously suggested test of all modified theories of gravity that would reproduce MOND at low accelerations. In a class of models, called "dark matter emulators", gravitational waves and other particles couple to different metrics. This leads to a detectable time lag between their detection at Earth from the same source. We calculate this time lag numerically for any event that occurs in our galaxy up to 400 kpc, and present a graph of this possible time lag. This suggests that, gravitational wave observers might have to consider the possibility of extending their analysis to non-coincident gravitational and electromagnetic signals, and the graph that we present might be a useful guideline for this effort.Comment: 5 pages, 2 figures, 2 tables, A New section is added and some equations were removed to avoid repetitio

Constraints on differential Shapiro delay between neutrinos and photons from IceCube-170922A

On 22nd September 2017, the IceCube Collaboration detected a neutrino with energy of about 290 TeV from the direction of the gamma-ray blazar TXS 0506+056, located at a distance of about 1.75 Gpc. During the same time, enhanced gamma-ray flaring was also simultaneously observed from multiple telescopes, giving rise to only the second coincident astrophysical neutrino/photon observation after SN 1987A. We point out that for this event, both neutrinos and photons encountered a Shapiro delay of about 6300 days along the way from the source. From this delay and the relative time difference between the neutrino and photon arrival times, one can constrain violations of Einstein's Weak Equivalence Principle (WEP) for TeV neutrinos. We constrain such violations of WEP using the Parameterized Post-Newtonian (PPN) parameter $\gamma$, which is given by $|\gamma_{\rm {\nu}}-\gamma_{\rm{EM}}|<5.5 \times 10^{-2}$, after assuming time difference of 175 days between neutrino and photon arrival times.Comment: 5 page

Interacting two-component fluid models with varying EoS parameter

In this paper, we consider Universe filled with two-component fluid. We study two different models. In the first model we assume barotropic fluid with the linear equation of state as the first component of total fluid. In the second model we assume Van der Waals gas as the first component of total fluid. In both models, the second component assumed generalized ghost dark energy. We consider also interaction between component and discuss, numerically, cosmological quantities for two different parametrization of EoS which varies with time. We consider this as a toy model of our Universe. We fix parameters of the model by using generalized second law of thermodynamics. Comparing our results with some observational data suggests interacting barotropic fluid with EoS parameter $\omega(t)=\omega_{0}\cos(tH)+\omega_{1}t\frac{\dot{H}}{H}$ and generalized ghost dark energy as an appropriate model to describe our Universe.Comment: 11 page, accepted in Int. J. of Geometric Methods in Modern Physic

Quantum gravity corrections to the conformally coupled scalar self-mass-squared on de Sitter II: kinetic-conformal cross terms

The present work is the second part of a series of computations for the self-mass-squared of the conformally coupled (CC) scalar interacting with gravitons. This work includes the kinetic-kinetic and kinetic-conformal parts, and thus completes the full scalar self-mass squared at one loop order in de Sitter background when combined with the conformal-conformal part previously evaluated. We use dimensional regularization and renormalize the results by subtracting appropriate counterterms. The self-mass squared is finally ready to quantum-correct the CC scalar field equation so that one can study the effect of inflationary produced gravitons on the CC scalar and its observational consequences.Comment: 44 pages, 31 tables, comments welcome, v2: made some clarifications, v3: matches the published version in PR

Higher Dimensional Metrics of Colliding Gravitational Plane Waves

We give a higher even dimensional extension of vacuum colliding gravitational plane waves with the combinations of collinear and non-collinear polarized four-dimensional metric. The singularity structure of space-time depends on the parameters of the solution.Comment: 4 pages RevTex