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

Galactic Shapiro Delay to the Crab Pulsar and limit on Einstein's Equivalence Principle Violation

We calculate the total galactic Shapiro delay to the Crab pulsar by including the contributions from the dark matter as well as baryonic matter along the line of sight. The total delay due to dark matter potential is about 3.4 days. For baryonic matter, we included the contributions from both the bulge and the disk, which are approximately 0.12 and 0.32 days respectively. The total delay from all the matter distribution is therefore 3.84 days. We also calculate the limit on violations of Einstein's equivalence principle by using observations of "nano-shot" giant pulses from the Crab pulsar with time-delay $<0.4$~ns as well as using time differences between radio and optical photons observed from this pulsar. Using the former, we obtain a limit on violation of Einstein's equivalence principle in terms of the PPN parameter $\Delta \gamma < 2.41\times 10^{-15}$. From the time-difference between simultaneous optical and radio observations, we get $\Delta \gamma < 1.54\times 10^{-9}$. We also point out differences in our calculation of Shapiro delay and that from two recent papers (arXiv:1612.00717 and arXiv:1608.07657), which used the same observations to obtain a corresponding limit on $\Delta \gamma$.Comment: 4 pages, 1 figure. Accepted for publication in Eur. Phys. Journal

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

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