scholarly journals Photon–Photon Interactions and the Opacity of the Universe in Gamma Rays

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 146
Author(s):  
Alberto Franceschini
Keyword(s):  
Gamma Rays ◽  
Personal Account ◽  
Fundamental Physics ◽  
Extragalactic Background Light ◽  
Substantial Modification ◽  
Global Coherence ◽  
Photon Interactions ◽  
Available Information ◽  
The Universe ◽  
Present Understanding

We discuss the topic of the transparency of the Universe in gamma rays due to extragalactic background light, and its cosmological and physical implications. Rather than a review, this is a personal account on the development of 30 years of this branch of physical science. Extensive analysis of the currently available information appears to us as revealing a global coherence among the astrophysical, cosmological, and fundamental physics data, or, at least, no evident need so far of substantial modification of our present understanding. Deeper data from future experiments will verify to what extent and in which directions this conclusion should be modified.

scholarly journals Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 220
Author(s):  
Emil Khalikov
Keyword(s):  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Cascade Model ◽  
Point Sources ◽  
Spectral Energy ◽  
Observation Data ◽  
Cherenkov Telescopes ◽  
The Universe

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

scholarly journals Background Light from Population III Stars

1987 ◽  
Vol 117 ◽  
pp. 414-414
Author(s):  
Jonathan C. McDowell
Keyword(s):  
Dark Matter ◽  
Background Radiation ◽  
Large Fraction ◽  
Rest Mass ◽  
Critical Density ◽  
Density Parameter ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Far Ultraviolet ◽  
The Universe

It has been proposed (e.g. Carr, Bond and Arnett 1984) that the first generation of stars may have been Very Massive Objects (VMOs, of mass above 200 M⊙) which existed at large redshifts and left a large fraction of the mass of the universe in black hole remnants which now provide the dynamical ‘dark matter’. The radiation from these stars would be present today as extragalactic background light. For stars with density parameter Ω* which convert a fraction ϵ of their rest-mass to radiation at a redshift of z, the energy density of background radiation in units of the critical density is ΩR = εΩ* / (1+z). The VMOs would be far-ultraviolet sources with effective temperatures of 105 K. If the radiation is not absorbed, the constraints provided by measurements of background radiation imply (for H =50 km/s/Mpc) that the stars cannot close the universe unless they formed at a redshift of 40 or more. To provide the dark matter (of one-tenth closure density) the optical limits imply that they must have existed at redshifts above 25.

A Tale of Two Infinities

2021 ◽  
Author(s):  
Gianfranco Bertone
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Gravitational Waves ◽  
Direct Detection ◽  
Traditional Approach ◽  
Fundamental Physics ◽  
Modern Cosmology ◽  
Nobel Prize In Physics ◽  
The Universe ◽  
Modern Astronomy

The spectacular advances of modern astronomy have opened our horizon on an unexpected cosmos: a dark, mysterious Universe, populated by enigmatic entities we know very little about, like black holes, or nothing at all, like dark matter and dark energy. In this book, I discuss how the rise of a new discipline dubbed multimessenger astronomy is bringing about a revolution in our understanding of the cosmos, by combining the traditional approach based on the observation of light from celestial objects, with a new one based on other ‘messengers’—such as gravitational waves, neutrinos, and cosmic rays—that carry information from otherwise inaccessible corners of the Universe. Much has been written about the extraordinary potential of this new discipline, since the 2017 Nobel Prize in physics was awarded for the direct detection of gravitational waves. But here I will take a different angle and explore how gravitational waves and other messengers might help us break the stalemate that has been plaguing fundamental physics for four decades, and to consolidate the foundations of modern cosmology.

scholarly journals CTA sensitivity for probing cosmology and fundamental physics with gamma rays

2021 ◽  
Author(s):  
Ievgen Vovk ◽  
Jonathan Biteau ◽  
Humberto - Martínez-Huerta ◽  
Manuel Meyer ◽  
Santiago Pita
Keyword(s):  
Gamma Rays ◽  
Fundamental Physics

scholarly journals The Search for Feebly Interacting Particles

2021 ◽  
Vol 71 (1) ◽  
pp. 279-313
Author(s):  
Gaia Lanfranchi ◽  
Maxim Pospelov ◽  
Philip Schuster
Keyword(s):  
Dark Matter ◽  
Particle Physics ◽  
Interaction Strength ◽  
New Physics ◽  
Fine Tuning ◽  
Experimental Program ◽  
Interacting Particles ◽  
Fundamental Physics ◽  
The Standard Model ◽  
The Universe

At the dawn of a new decade, particle physics faces the challenge of explaining the mystery of dark matter, the origin of matter over antimatter in the Universe, the apparent fine-tuning of the electroweak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves New Physics at mass scales comparable to that of familiar matter—below the GeV scale but with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and existing data may even provide hints of this possibility. Emboldened by the lessons of the LHC, a vibrant experimental program to discover such physics is underway, guided by a systematic theoretical approach that is firmly grounded in the underlying principles of the Standard Model. We give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs, and we focus in particular on accelerator-based experiments.

scholarly journals The gravitational-wave physics

2017 ◽  
Vol 4 (5) ◽  
pp. 687-706 ◽  
Author(s):  
Rong-Gen Cai ◽  
Zhoujian Cao ◽  
Zong-Kuan Guo ◽  
Shao-Jiang Wang ◽  
Tao Yang
Keyword(s):  
Gravitational Wave ◽  
Gravitational Waves ◽  
Laser Interferometer ◽  
Direct Detection ◽  
Fundamental Physics ◽  
First Order ◽  
Compact Binary ◽  
First Order Phase Transition ◽  
First Order Phase ◽  
The Universe

Abstract The direct detection of gravitational wave by Laser Interferometer Gravitational-Wave Observatory indicates the coming of the era of gravitational-wave astronomy and gravitational-wave cosmology. It is expected that more and more gravitational-wave events will be detected by currently existing and planned gravitational-wave detectors. The gravitational waves open a new window to explore the Universe and various mysteries will be disclosed through the gravitational-wave detection, combined with other cosmological probes. The gravitational-wave physics is not only related to gravitation theory, but also is closely tied to fundamental physics, cosmology and astrophysics. In this review article, three kinds of sources of gravitational waves and relevant physics will be discussed, namely gravitational waves produced during the inflation and preheating phases of the Universe, the gravitational waves produced during the first-order phase transition as the Universe cools down and the gravitational waves from the three phases: inspiral, merger and ringdown of a compact binary system, respectively. We will also discuss the gravitational waves as a standard siren to explore the evolution of the Universe.

scholarly journals Physical Constraints on Models of Gamma-Ray Bursters

1986 ◽  
Vol 89 ◽  
pp. 305-321
Author(s):  
Richard I. Epstein
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
Burst Source ◽  
Gamma Ray Burst ◽  
Physical Constraints ◽  
Low Energies ◽  
Energy Gamma ◽  
Photon Interactions

AbstractThe power per logarithmic bandwidth in gamma-ray burst spectra generally increases rapidly with energy through the x-ray range and does not cut off sharply above a few MeV. This spectral form indicates that a very small fraction of the energy from a gamma-ray burst source is emitted at low energies or is reprocessed into x-rays and that the high-energy gamma rays are not destroyed by photon-photon interactions. The implications are that the emission mechanism for the gamma-ray bursts is not synchrotron radiation from electrons that lose most of their energy before being re-accelerated and that either the regions from which the gamma rays are emitted are large compared to the size of a neutron star or the emission is collimated and beamed away from the stellar surface.

scholarly journals Summary Talk : Multi-Wavelength Sky Surveys

1998 ◽  
Vol 179 ◽  
pp. 493-499
Author(s):  
O. Lahav
Keyword(s):  
Gamma Rays ◽  
Dimensional Space ◽  
Instrument Design ◽  
List Type ◽  
Type Number ◽  
Sky Surveys ◽  
3 Dimensional ◽  
Multi Wavelength ◽  
The Universe ◽  
Summary Talk

An astronomer's career can be viewed in a 3-dimensional space where the (nearly orthogonal) axes are : – the objects of interest (from planets to the Universe),– techniques (from instrument design to analytic calculations),– the wavelength (from the radio to gamma rays).

Cosmology: evidence for a ‘big bang’

1994 ◽  
Vol 2 (2) ◽  
pp. 155-164
Author(s):  
Martin J. Rees
Keyword(s):  
Present State ◽  
Background Radiation ◽  
Cosmic Background Radiation ◽  
Big Bang ◽  
Fundamental Physics ◽  
Cosmic Expansion ◽  
Cosmic Background ◽  
The Universe

During the last 25 years, evidence has accumulated that our universe has evolved, over a period of 10–15 billion years, from a hot dense fireball to its present state. Telescopes can detect objects so far away that the universe had only a tenth its present age when the light we now receive set out towards us. The cosmic background radiation, and the abundances of elements such as helium and lithium, permit quantitative inferences about what the universe was like when it had been expanding for only a few seconds. The laws of physics established in the laboratory apparently suffice for interpreting all astronomical phenomena back to that time. In the initial instants of cosmic expansion, however, the particle energies and densities were so extreme that terrestrial experiments offer no firm guidance. We will not understand why the universe contains the observed ‘mix’ of matter and radiation, nor why it is expanding in the observed fashion, without further progress in fundamental physics.

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