This volume celebrates the 30th anniversary of the first very-high energy (VHE) gamma-ray Source detection: the Crab Nebula, observed by the pioneering ground-based Cherenkov telescope Whipple, at ...teraelectronvolts (TeV) energies, in 1989. As we entered a new era in TeV astronomy, with the imminent start of operations of the Cherenkov Telescope Array (CTA) and new facilities such as LHAASO and the proposed Southern Wide-Field Gamma-ray Observatory (SWGO), we conceived of this volume as a broad reflection on how far we have evolved in the astrophysics topics that dominated the field of TeV astronomy for much of recent history.In the past two decades, H.E.S.S., MAGIC and VERITAS pushed the field of TeV astronomy, consolidating the field of TeV astrophysics, from few to hundreds of TeV emitters. Today, this is a mature field, covering almost every topic of modern astrophysics. TeV astrophysics is also at the center of the multi-messenger astrophysics revolution, as the extreme photon energies involved provide an effective probe in cosmic-ray acceleration, propagation and interaction, in dark matter and exotic physics searches. The improvement that CTA will carry forward and the fact that CTA will operate as the first open observatory in the field, mean that gamma-ray astronomy is about to enter a new precision and productive era.This book aims to serve as an introduction to the field and its state of the art, presenting a series of authoritative reviews on a broad range of topics in which TeV astronomy provided essential contributions, and where some of the most relevant questions for future research lie.
It is well-known that the universe is opaque to the propagation of Ultra-High-Energy Cosmic Rays (UHECRs) since these particles dissipate energy during their propagation interacting with the ...background fields present in the universe, mainly with the Cosmic Microwave Background (CMB) in the so-called GZK cut-off phenomenon. Some experimental evidence seems to hint at the possibility of a dilation of the GZK predicted opacity sphere. It is well-known that kinematical perturbations caused by supposed quantum gravity (QG) effects can modify the foreseen GZK opacity horizon. The introduction of Lorentz Invariance Violation can indeed reduce, and in some cases making negligible, the CMB-UHECRs interaction probability. In this work, we explore the effects induced by modified kinematics in the UHECR lightest component phenomenology from the QG perspective. We explore the possibility of a geometrical description of the massive fermions interaction with the supposed quantum structure of spacetime in order to introduce a Lorentz covariance modification. The kinematics are amended, modifying the dispersion relations of free particles in the context of a covariance-preserving framework. This spacetime description requires a more general geometry than the usual Riemannian one, indicating, for instance, the Finsler construction and the related generalized Finsler spacetime as ideal candidates. Finally we investigate the correlation between the magnitude of Lorentz covariance modification and the attenuation length of the photopion production process related to the GZK cut-off, demonstrating that the predicted opacity horizon can be dilated even in the context of a theory that does not require any privileged reference frame.
Searching for local Lorentz invariance violation (LIV) is a method to probe general relativity (GR), since local Lorentz invariance is a key ingredient for GR. Here, we first review the work we have ...done on LIV in the pure‐gravity sector involving quadratic couplings of Riemann curvature through short‐range pendulum experiments, especially focusing on the theoretical model we established for the transfer matrix linking the experimentally measured torque signal to the 14 LIV coefficients. Based on this model, we analyze the LIV effect in HUST‐2011 and HUST‐2015 experiments again, and give the constraints for the 14 measurable violating coefficients in both experiments. Furthermore, we propose a new experimental design aiming at exploring LIV, which may independently constrain the 14 LIV coefficients with higher sensitivity (improved by about an order of magnitude over earlier results) using the striped geometry.
Local Lorentz invariance is an important component of General Relativity. Testing for Local Lorentz invariance can not only probe the foundation stone of General Relativity but also help to explore ...the unified theory for General Relativity and quantum mechanics. In this paper, we search the Local Lorentz invariance violation associated with operators of mass dimension d = 6 in the pure-gravity sector with short-range gravitational experiments. To enlarge the Local Lorentz invariance violation signal effectively, we design a new experiment in which the constraints of all fourteen violation coefficients may be improved by about one order of magnitude.
Spontaneous Lorentz violation realized through a nonlinear vector field constraint of the type
A
μ
A
μ
=
M
2
(
M is the proposed scale for Lorentz violation) is shown to generate massless vector ...Goldstone bosons, gauging the starting global internal symmetries in arbitrary relativistically invariant theories. The gauge invariance appears in essence as a necessary condition for these bosons not to be superfluously restricted in degrees of freedom, apart from the constraint due to which the true vacuum in a theory is chosen by the Lorentz violation. In the Abelian symmetry case the only possible theory proves to be QED with a massless vector Goldstone boson naturally associated with the photon, while the non-Abelian symmetry case results in a conventional Yang–Mills theory. These theories, both Abelian and non-Abelian, look essentially nonlinear and contain particular Lorentz (and
CPT) violating couplings when expressed in terms of the pure Goldstone vector modes. However, they do not lead to physical Lorentz violation due to the simultaneously generated gauge invariance.
This paper deals with the violation of Lorentz symmetry. The approach is based on Compton scattering which becomes modified due to a modified dispersion relation arising from a minimum spacetime cut ...off as in modern Quantum Gravity approaches. With this amendment, we find that two high-energy rays of different energies develop a time-lag. This time separation becomes prominent when the energies of the considered photons is ≥ 1
GeV
. Extending our approach to gamma rays of cosmic origin we predict that they undergo innumerable such scattering processes before reaching us. Therefore, it accounts for the time-lag phenomena of
gamma ray bursts
(
GRB
)’s which have been claimed to be observed. Also, we find that resorting to the modified
Snyder-Sidharth Hamiltonian
it is possible to extend the
GZK cut off
beyond its normal limit, 10
20
eV
. Some observations of ultra high energy cosmic rays support this. This extends the limits of special theory of relativity.
In the present work, an expression for Planck mass or Planck energy is derived by equating the Compton wavelength with the gravitational radius of the Kerr rotating body. Using the modified photon ...energy–momentum dispersion relation, the variation of the photon propagation speed with photon frequency is derived. It is found that, the photon propagation speed, depends on the frequency of the photon, the rotation parameter of the Kerr rotating body and also on the polarization state of the photon. Quantum gravity effect could be seen from the derived results for the photon propagation speed.
The connection between Lorentz invariance violation and noncommutativity of fields in a quantum field theory is investigated. A new dispersion relation for a free field theory with just one ...additional noncommutative parameter is obtained. While values for the noncommutative scale much larger than 10−20 eV−1 are ruled out by the present experimental status, cosmic ray physics would be compatible with and sensible to a noncommutativity arising from quantum gravity effects. We explore the matter–antimatter asymmetry which is naturally present in this framework.
We show for the first time that the induced parity-even Lorentz invariance violation can be unambiguously calculated in the physically justified and minimally broken, dimensional regularization ...scheme, suitably tailored for a spontaneous Lorentz symmetry breaking in a field theory model. The quantization of the Lorentz invariance violating quantum electrodynamics is critically examined and shown to be consistent either for a light-like cosmic anisotropy axial-vector or for a time-like one, when in the presence of a bare photon mass.
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