Abstract: We build an infinite class of exact axisymmetric solutions of a metric-affine gravity theory, namely, Eddington-inspired Born-Infeld gravity, coupled to an anisotropic fluid as a matter source. The solution-generating method employed is not unique of this theory but can be extended to other Ricci-Based Gravity theories (RBGs), a class of theories built out of contractions of the Ricci tensor with the metric. This method exploits a correspondence between the space of solutions of General Relativity and that of RBGs, and is independent of the symmetries of the problem. For the particular case in which the fluid is identified with non-linear electromagnetic fields we explicitly derive the corresponding axisymmetric solutions. Finally, we use this result to work out the counterpart of the Kerr-Newman black hole when Maxwell electrodynamics is set on the metric-affine side. Our results open up an exciting new avenue for testing new gravitational phenomenology in the fields of gravitational waves and shadows out of rotating black holes.

Abstract: We examine the impact of Lorentz Invariance Violation (LIV) in measuring the octant of theta(23) and CP phases in the context of the Deep Underground Neutrino Experiment (DUNE). We consider the CPT-violating LIV parameters involving e-mu(a(e mu)) and e-tau (a(e tau)) flavors, which induce an additional interference term in neutrino and antineutrino appearance probabilities. This newinterference term depends on both the standard CP phase delta and the new dynamical CP phase phi(e mu)/phi(e tau), giving rise to new degeneracies among (theta(23), delta, phi). Taking one LIV parameter at-a-time and considering a small value of vertical bar a(e mu)vertical bar = vertical bar a(e tau)vertical bar = 5 x 10(-24) GeV, we find that the octant discovery potential of DUNE gets substantially deteriorated for unfavorable combinations of delta and phi(e mu)/phi(e tau). The octant of theta(23) can only be resolved at 3 sigma if the true value of sin(2) theta(23) less than or similar to 0.42 or >= 0.62 for any choices of delta and phi. Interestingly, we also observe that when both the LIV parameters a(e mu) and a(e tau) are present together, they cancel out the impact of each other to a significant extent, allowing DUNE to largely regain its octant resolution capability. We also reconstruct the CP phases delta and phi(e mu)/phi(e tau). The typical 1 sigma uncertainty on delta is 10-15 degrees. and the same on phi(e mu)/phi(e tau) is 25-30 degrees depending on the choices of their true values.

Abstract: The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising gravitational sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of the workshop “Challenges and opportunities of high-frequency gravitational wave detection” held at ICTP Trieste, Italy in October 2019, that set up the stage for the recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW) initiative.