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The speed of light ($c$) in a vacuum is independent on a choice of frames to describe the propagation, according to the theory of relativity. We consider how light is characterised in a material, where the speed of light is different from…

Optics · Physics 2024-06-07 Shinichi Saito

In this work, I develop an alternative explanation for the acceleration of the cosmic expansion, which seems to be a result of recent high redshift Supernova data. In the current interpretation, this cosmic acceleration is explained by…

General Relativity and Quantum Cosmology · Physics 2007-05-23 J. -F. Pascual-Sánchez

General Relativistic Entropic Acceleration (GREA) theory provides a covariant formalism for out-of-equilibrium phenomena in GR, extending the Einstein equations with an entropic force that behaves like bulk viscosity with a negative…

Cosmology and Nongalactic Astrophysics · Physics 2024-05-28 Juan Garcia-Bellido

Bulk peculiar flows are commonplace in the universe, with many surveys reporting their presence on scales spanning between few hundred and several hundred Mpc. However, the sizes and the speeds of some of these bulk flows are well in excess…

General Relativity and Quantum Cosmology · Physics 2025-11-26 Christos G. Tsagas

In the context of a cosmological study of the bulk flows in the Universe, we present a detailed study of the statistical properties of the kinematic Sunyaev-Zel'dovich (kSZ) effect. We first compute analytically the correlation function and…

Astrophysics · Physics 2009-11-13 C. Hernandez-Monteagudo , L. Verde , Raul Jimenez , D. N. Spergel

Matter accreting onto black holes may develop shocks due to the centrifugal barrier. A part of inflowing matter in the post-shock flow is deflected along the axis in the form of jets. Post-shock flow which behaves like a Compton cloud has…

Astrophysics · Physics 2009-11-07 Indranil Chattopadhyay , Sandip K. Chakrabarti

Phenomenological models of cosmic-ray (CR) transport in the Milky Way (MW) can reproduce a wide range of observations assuming that CRs scatter off of magnetic-field fluctuations with spectrum $\propto k^{-\delta}$ and $\delta \sim…

High Energy Astrophysical Phenomena · Physics 2022-06-15 Philipp Kempski , Eliot Quataert

The meaning of "linear expansion" is explained. Particularly accurate relative distances are compiled and homogenized a) for 246 SNe Ia and 35 clusters with v<30,000 km/s, and b) for relatively nearby galaxies with 176 TRGB and 30 Cepheid…

Cosmology and Nongalactic Astrophysics · Physics 2015-03-13 A. Sandage , B. Reindl , G. A. Tammann

We review the increasing evidence for the cosmological relevance of the cold local Hubble flow. New observations, N-body simulations and other theoretical arguments are discussed, supporting our previous suggestion that the cosmological…

Astrophysics · Physics 2009-11-11 Pekka Teerikorpi , Arthur D. Chernin , Yurij V. Baryshev

We present the first general relativistic hydrodynamic models of the launch and evolution of relativistic jets and winds, driven by thermal energy deposition, possibly due to neutrino-antineutrino annihilation, in the close vicinity of…

Astrophysics · Physics 2015-06-24 M. A. Aloy , H. -T. Janka , E. Mueller

Recently, observational data and high precision mapping of the local velocity field of Local Group and Virgo cluster have revealed a linear velocity-distance relation of the outermost galaxies, properly referred to as Local Hubble Flow. By…

Astrophysics of Galaxies · Physics 2016-02-03 Martina Donnari , Marco Merafina , Manuel Arca-Sedda

Recent detections of high-energy $\gamma$-rays from behind-the-limb (BTL) solar flares by the \emph{Fermi $\gamma$-ray Space Telescope} pose a puzzle and challenge on the particle acceleration and transport mechanisms. In such events, the…

We study a phenomenological dark matter model described as a collisionless relativistic kinetic gas in a spatially flat Friedmann-Lema\^itre-Robertson-Walker universe. After normalization to the observed present-day dark matter abundance,…

General Physics · Physics 2026-02-10 Francisco X. Linares Cedeño , Ulises Nucamendi , Olivier Sarbach

A beginning end-point for galaxy motions within the 10-Mpc Local Volume is constructed by requiring a smooth distribution of (luminous) mass at the time of recombination, which is shown to be equivalent to a smooth Hubble flow at early…

Astrophysics · Physics 2008-11-26 Alan B. Whiting

Observed accretion rates onto the Milky-Way and other local spirals fall short of that required to sustain star formation for cosmological timescales. A potential avenue for this unseen accretion is an inflow in the volume-filling hot phase…

The cosmological peculiar velocity field (deviations from the pure Hubble flow) of matter carries significant information on dark energy, dark matter and the underlying theory of gravity on large scales. Peculiar motions of galaxies…

Cosmology and Nongalactic Astrophysics · Physics 2013-01-17 Adi Nusser , Enzo Branchini , Martin Feix

In this essay, I present an alternative explanation for the cosmic acceleration which appears as a consequence of recent high redshift Supernova data. In the usual interpretation, this cosmic acceleration is explained by the presence of a…

General Relativity and Quantum Cosmology · Physics 2009-10-31 J. -F. Pascual-Sánchez

Peculiar motion introduces systematic variations in the observed luminosity distribution of galaxies. This allows one to constrain the cosmic peculiar velocity field from large galaxy redshift surveys. Using around half a million galaxies…

Cosmology and Nongalactic Astrophysics · Physics 2016-10-19 Martin Feix , Adi Nusser , Enzo Branchini

With the next generation of big telescopes such as the ELT and SKA it might become possible to measure changes in the expansion rate of the Universe in real time by measuring the change of the redshifts of a large number of galaxies over a…

Cosmology and Nongalactic Astrophysics · Physics 2025-12-02 Nico Roos , Eric Sluimer , Bert van den Broek

On the basis of a previously established scalar-tensor extension of the $\Lambda$CDM model we develop an effective fluid approach for the matter growth function. This extended $\Lambda$CDM (henceforth $e_{\Phi}\Lambda$CDM) cosmology takes…

Cosmology and Nongalactic Astrophysics · Physics 2019-05-01 W. Zimdahl , H. E. S. Velten , W. C. Algoner