Recently it has become clear that the resonant amplification of quantum field fluctuations at preheating must be accompanied by resonant amplification of scalar metric perturbations, since the two are united by Einstein's equations. Furthermore, this "metric preheating" enhances particle production and leads to gravitational rescattering effects even at linear order. In multi-field models with strong preheating (q \gg 1), metric perturbations are driven nonlinear, with the strongest amplification typically on super-Hubble scales (k \to 0). This amplification is causal, being due to the super- Hubble coherence of the inflaton condensate, and is accompanied by resonant growth of entropy perturbations. The amplification invalidates the use of the linearized Einstein field equations, irrespective of the amount of fine-tuning of the initial conditions. This has serious implications at all scales - from the large-angle cosmic microwave background (CMB) anisotropies to primordial black holes. We investigate the (q,k) parameter space in a two-field model, and introduce the time to nonlinearity, t_{nl}, as the timescale for the breakdown of the linearized Einstein equations. Backreaction effects are expected to shut down the linear resonances, but cannot remove the existing amplification, which threatens the viability of strong preheating when confronted with the CMB. We discuss ways to escape the above conclusions, including secondary phases of inflation and preheating solely to fermions. Finally we rank known classes of inflation from strongest (chaotic and strongly coupled hybrid inflation) to weakest (hidden sector, warm inflation) in terms of the distortion of the primordial spectrum due to these resonances in preheating.Comment: 31 pages, 16 figures, Revtex. Final version. Nuclear Physics B (in press

We present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum (OAM). This physical observable allows a direct measurement of the rotation of the black hole. We extracted the OAM spectra from the radio intensity data collected by the Event Horizon Telescope from around the black hole M87* by using wavefront reconstruction and phase recovery techniques and from the visibility amplitude and phase maps. This method is robust and complementary to black-hole shadow circularity analyses. It shows that the M87* rotates clockwise with an estimated rotation parameter a = 0.90 ± 0.05 with ∼ 95% confidence level (c.l.) and inclination i = 17 • ± 2 • , equivalent to a magnetic arrested disk with inclination i = 163 • ± 2 • . From our analysis we conclude, within a 6 σ c.l., that the M87* is rotating.

Einstein's equations of general relativity (GR) can describe the connection between events within a given hypervolume of size L larger than the Planck length L P in terms of wormhole connections where metric fluctuations give rise to an indetermination relationship that involves the Riemann curvature tensor. At low energies (when L ≫ L P ), these connections behave like an exchange of a virtual graviton with wavelength λ G = L as if gravitation were an emergent physical property. Down to Planck scales, wormholes avoid the gravitational collapse and any superposition of events or space-times become indistinguishable. These properties of Einstein's equations can find connections with the novel picture of quantum gravity (QG) known as the "Einstein-Rosen (ER)=Einstein-Podolski-Rosen (EPR)" (ER = EPR) conjecture proposed by Susskind and Maldacena in Anti-de-Sitter (AdS) space-times in their equivalence with conformal field theories (CFTs). In this scenario, non-traversable wormhole connections of two or more distant events in space-time through Einstein-Rosen (ER) wormholes that are solutions of the equations of GR, are supposed to be equivalent to events connected with non-local Einstein-Podolski-Rosen (EPR) entangled states that instead belong to the language of quantum mechanics. Our findings suggest that if the ER = EPR conjecture is valid, it can be extended to other different types of space-times and that gravity and space-time could be emergent physical quantities if the exchange of a virtual graviton between events can be considered connected by ER wormholes equivalent to entanglement connections.

Grand unified theories may display multiply interacting fields with strong coupling dynamics. This poses two new problems: (1) what is the nature of chaotic reheating after inflation, and (2) how is reheating sensitive to the mass spectrum of these theories ? We answer these questions in two interesting limiting cases and demonstrate an increased efficiency of reheating which strongly enhances non-thermal topological defect formation, including monopoles and domain walls. Nevertheless, the large fluctuations may resolve this monopole problem via a modified Dvali-Liu-Vachaspati mechanism in which non-thermal destabilsation of discrete symmetries occurs at reheating. An ideal inflationary scenario should arise naturally from within supergravity or a Grand Unified Theory (GUT) without fine-tuning. It should solve the plethora of problems of standard cosmology while simultaneously diltuting the monopoles inevitably produced due to the homotopic content π 2 (G/U (1)) ≃ π 1 (U (1)) ≃ Z of the standard model. Significant progress has been made within GUT's and supersymmetric theories towards this utopic vision [1,2]. However, the issue of reheating after inflation in these theories, where the universe is revived, phoenix-like, from the frozen vacuum state, has remained relatively unexplored [3]. This is precisely one area where the full symmetry and particle content of the underlying theory is likely to be crucial. SISSA-42Indeed reheating poses a severe threat to the simple ideal presented above since non-perturbative effects are typically dominant [4][5][6][7]. Reheating is therefore not a minor phase at the end of inflation, of little dynamical interest. The large quantum fluctuations allow for GUT baryogenesis [8,5] and, as pointed out by Kofman et al [4], may cause the monopole and domain wall problems to reappear due to non-thermal symmetry restoration. This last possibility is actually rather difficult in simple models of reheating with only two fields [6]. As we shall show, however, this situation changes dramatically in the case of multiple fields, relevant for GUT models.The main motivation of this work then is to understand what new effects multiple fields have on reheating. This issue encompasses two particularly interesting unknowns. (i) The nature of reheating at strong coupling when the fields evolve chaotically. This is relevant for GUT's with divergent UV fixed points [9,10] and models such as softly broken Seiberg-Witten inflation [11] where reheating occurs in the strongly coupled, confining, regime. Setting aside the subtle issue of the quantum behaviour of gauge theories at strong coupling [12], in the two and three scalar-field cases studied so far, (classical) chaotic motion has been typical [13], especially at reheating. This chaotic evolution parallels results in the Einstein-Yang-Mills equations [14], semi-classical QCD and lattice gauge theory [15]. Thus a natural question is "what is the nature of chaotic reheating ?"The second issue is (ii) the sensitivity of reheating to the mass spectrum ...

In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.X-ray, Black holes physics, accretion PACS number(s): 97.60. Lf, 98.54.Cm, 98.62.Js, 98.62.Mw, 97.80.Jp, 95.55.Ka, 04.80.y