Apparent Correction to the Speed of Light in a Gravitational Potential

标量–Einstein–Gauss–Bonnet引力中引力波的传播速度

Propagation Speed of Gravitational Wave in Scalar--Einstein--Gauss-Bonnet Gravity

本文研究 sEGB 引力中的引力波速度，构造满足宇宙学光速传播且可现实暴胀的理论，并指出其与黑洞背景条件不相容。

Apparent horizon formation in the head-on collision of gyratons

The gyraton model describes a gravitational field of an object moving with the velocity of light which has finite energy and spin distributed during some finite time interval $L$. A gyraton may be considered as a classical toy model for a quantum wave packet of high-energy particles with spin. In this paper we study a head-on collision of two gyratons and black hole formation in this process. The goal of this study is to understand the role of the gravitational spin-spin interaction in the process of mini-black-hole formation in particle collisions. To simplify the problem we consider several …

Apparent Superluminal Muon-neutrino Velocity as a Manifestation of Weak Value

The result of the OPERA experiment revealed that the velocity of muon-neutrinos was larger than the speed of light. We argue that this apparent superluminal velocity can be interpreted as a weak value, which is a new concept recently studied in the context of quantum physics. The OPERA experiment setup forms a scheme that manifests the neutrino velocity as a weak value. The velocity defined in the scheme of weak measurement can exceed the speed of light. The weak velocity is not a concept associated to a single phenomenon but it is a statistical concept defined by accumulating data at separate…

Einstein's gravitational lensing and nonlinear electrodynamics

In 1936 Einstein predicted the phenomenon presently known as gravitational lensing (GL). A prime feature of GL is the magnification, because of the gravitational field, of the star visible surface as seen from a distant observer. We show here that nonlinear electrodynamics (NLED) modifies in a fundamental basis Einstein's general relativistic (GR) original derivation. The effect becomes apparent by studying the light propagation from a strongly magnetic ($B$) pulsar (SMP). Unlike its GR counterpart, the photon dynamics in NLED leads to a new effective GL, which depends also on the $B$-field pe…

Gauss-Bonnet耦合暴胀中的引力波声速共振

Sound Speed Resonance of Gravitational Waves in Gauss-Bonnet-coupled inflation

本文证明了在Gauss-Bonnet耦合暴胀中，暴胀子振荡引起的张量模式声速阻尼振荡会导致引力波共振放大，并指出该信号可被SKA、DECIGO和BBO等实验探测。

Sound speed resonance of the stochastic gravitational wave background

We propose a novel mechanism to test time variation of the propagation speed of gravitational waves (GWs) in light of GWs astronomy. As the stochastic GWs experience the whole history of cosmic expansion, they encode potential observational evidence of such variation. We report that, one feature of a varying GWs speed is that the energy spectrum of GWs will present resonantly-enhanced peaks if the GWs speed oscillates in time at high-energy scales. Such oscillatory behaviour arises in a wide class of modified gravity theories. The amplitude of these peaks can be at reach by current and forthco…

Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than $10^{-15}c$. Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range $…

Is Cosmic Speed-Up Due to New Gravitational Physics?

We show that cosmic acceleration can arise due to very tiny corrections to the usual gravitational action of General Relativity of the form $R^n$, with $n<0$. This eliminates the need for dark energy, though it does not address the cosmological constant problem. Since a modification to the Einstein-Hilbert action of the form $R^n$, with $n>0$, can lead to early-time inflation, our proposal provides a unified and purely gravitational origin for the early and late time accelerating phases of the Universe.

Speed of sound in cosmological phase transitions and effect on gravitational waves

The energy budget for gravitational waves of a cosmological first order phase transitions depends on the speed of sound in the thermal plasma in both phases around the bubble wall. Working in the real-singlet augmented Standard Model, which admits a strong two-step electroweak phase transition, we compute higher order corrections to the pressure and sound speed. We compare our result to lower-order approximations to the sound speed and the energy budget and investigate the impact on the gravitational wave signal. We find that deviations in the speed of sound from $c_s^2 = 1/3$ are enhanced up …

Implications of Cosmic Repulsion for Gravitational Theory

In this paper we present a general, model independent analysis of a recently detected apparent cosmic repulsion, and discuss its potential implications for gravitational theory. In particular, we show that a negatively spatially curved universe acts like a diverging refractive medium, to thus naturally cause galaxies to accelerate away from each other. Additionally, we show that it is possible for a cosmic acceleration to only be temporary, with some accelerating universes actually being able to subsequently recontract.

Horndeski 速度测试与标量-光子耦合

Horndeski speed tests with scalar-photon couplings

本文重新审视了中子星合并多信使观测对 Horndeski 及 beyond Horndeski 理论中引力波与电磁波速度的约束，研究了暗能量场与电磁场的非平凡耦合如何改变唯象限制，并指出标量-光子高阶耦合与多信使速度测试及引力波衰变约束不相容。