Search results for "Relativity"
showing 10 items of 1213 documents
Lepton number asymmetries and the lower bound on the reheating temperature
2017
We show that the reheating temperature of a matter-domination era in the early universe can be pushed down to the neutrino decoupling temperature at around $2 \ {\rm MeV}$ if the reheating takes place through non-hadronic decays of the dominant matter and neutrino-antineutrino asymmetries are still large enough, $|L| \gtrsim \mathcal{O}(10^{-2})$ (depending on the neutrino flavor) at the end of reheating.
Emergent Dark Energy, neutrinos and cosmological tensions
2020
The Phenomenologically Emergent Dark Energy model, a dark energy model with the same number of free parameters as the flat $\Lambda$CDM, has been proposed as a working example of a minimal model which can avoid the current cosmological tensions. A straightforward question is whether or not the inclusion of massive neutrinos and extra relativistic species may spoil such an appealing phenomenological alternative. We present the bounds on $M_{\nu}$ and $N_{\rm eff}$ and comment on the long standing $H_0$ and $\sigma_8$ tensions within this cosmological framework with a wealth of cosmological observations. Interestingly, we find, at $95\%$ confidence level, and with the most complete set of cos…
Search for Quantum Black Hole Production in High-Invariant-MassLepton+JetFinal States UsingppCollisions ats=8 TeVand the ATLAS Detector
2014
This Letter presents a search for quantum black-hole production using 20.3 fb(-1) of data collected with the ATLAS detector in pp collisions at the LHC at root s = 8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton + jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black hol…
Gravity and handedness of photons
2017
Vacuum fluctuations of quantum fields are altered in presence of a strong gravitational background, with important physical consequences. We argue that a non-trivial spacetime geometry can act as an optically active medium for quantum electromagnetic radiation, in such a way that the state of polarization of radiation changes in time, even in the absence of electromagnetic sources. This is a quantum effect, and is a consequence of an anomaly related to the classical invariance under electric-magnetic duality rotations in Maxwell theory.
Lens Effect and CMB Anisotropies: Simulations
2003
Cosmological structures deviate the photons of the Cosmic Microwave Background (CMB). The resulting deviations can be calculated moving photons in the gravitational field of realistic lens distributions obtained from numerical simulations. The main goal of this paper is answering the following question: Which types of numerical simulations are appropriate to study angular CMB deformations caused by lensing?
Spontaneous creation of circularly polarized photons in chiral astrophysical systems
2020
This work establishes a relation between chiral anomalies in curved spacetimes and the radiative content of the gravitational field. In particular, we show that a flux of circularly polarized gravitational waves triggers the spontaneous creation of photons with net circular polarization from the quantum vacuum. Using waveform catalogues we identify precessing binary black holes as astrophysical configurations that emit such gravitational radiation, and then solve the fully non-linear Einstein's equations with numerical relativity to evaluate the net effect. The quantum amplitude for a merger is comparable to the Hawking emission rate of the final black hole, and small to be directly observe…
Local Lorentz invariance tests for photons and hadrons at the Gamma Factory
2021
High-precision tests of local Lorentz invariance, via monitoring of the sidereal time variation of the photon energies emitted by ultrarelativistic heavy-ion beams and of the beam momentum, are proposed. This paper includes descriptions of the physics ideas and the concept for the detector. The experiment results will allow high-precision tests of LLI via anisotropy of the maximum attainable speed of a photon and an ion. The projected accuracy for the asymmetries interpreted in the framework of the anisotropic relativistic mechanics corresponds to the limit on sidereal time variation of the one-way maximum attainable speed at the levels between $10^{-14}$ and $10^{-17}$.
Photospheric response to an ellerman bomb-like event—an analogy of Sunrise/IMaX observations and MHD simulations
2017
S. Danilovic et. al.
Higher-order gravity in higher dimensions: geometrical origins of four-dimensional cosmology?
2017
Determining cosmological field equations represents a still very debated matter and implies a wide discussion around different theoretical proposals. A suitable conceptual scheme could be represented by gravity models that naturally generalize Einstein Theory like higher order gravity theories and higher dimensional ones. Both of these two different approaches allow to define, at the effective level, Einstein field equations equipped with source-like energy momentum tensors of geometrical origin. In this paper, it is discussed the possibility to develop a five dimensional fourth order gravity model whose lower dimensional reduction could provide an interpretation of cosmological four dimens…
Null conformal Killing-Yano tensors and Birkhoff theorem
2015
We study the space-times admitting a null conformal Killing-Yano tensor whose divergence defines a Killing vector. We analyze the similitudes and differences with the recently studied non null case (Gen. Relativ. Grav. (2015) {\bf 47} 1911). The results by Barnes concerning the Birkhoff theorem for the case of null orbits are analyzed and generalized.