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Andrea Addazi

Publications and source records attributed to Andrea Addazi.

At least 91 records · Page 5Linked to original sources

Self-dual formulation of gravity in topological M-theory

Inspired by the low wave-length limit of topological M-theory, which re-constructs the theory of $3+1$D gravity in the self-dual variables' formulation, and by the realization that in Loop Quantum Gravity the holonomy of a flat connection can be non-trivial if and only if a non-trivial (space-like) line defect is localized inside the loop, we argue that non-trivial gravitational holonomies can be put in correspondence with space-like M-branes. This suggests the existence of a new duality, which we call $H$ duality, interconnecting topological M-theory with Loop Quantum Gravity. We spell some arguments to show that fundamental S-strings are serious candidates to be considered in order to instantiate this correspondence to classes of LQG states. In particular, we consider the case of the holonomy flowers in LQG, and show that for this type of states the action of the Hamiltonian constraint, from the M-theory side, corresponds to a linear combination of appearance and disappearance of a SNS1- strings. Consequently, these processes can be reinterpreted, respectively, as enucleations or decays into open or closed strings.

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Testing Dark Matter Models with Radio Telescopes in light of Gravitational Wave Astronomy

In this Letter we put forward a novel phenomenological paradigm in which particle physics beyond the Standard Model may be tested by radio astronomy if they are related to a first order phase transition in the early Universe. For this type of Dark Matter models, the first order phase transition takes place at KeV scales, and hence, induces the production of a stochastic gravitational wave background that can be detected from Pulsar timing measures. We demonstrate this hypothetical feasibility by studying a class of Majoron Dark Matter model, which is related to a first order phase transition of the $U(1)_{L}$ or $U(1)_{B-L}$ symmetry and is consequently dubbed as {\it violent Majoron}. This phenomenon are expected to be examined by the ongoing and forthcoming radio experiments, including FAST, SKA and IPTA.

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Limiting Majoron self-interactions from Gravitational waves experiments

We show how Majoron models may be tested/limited in gravitational waves experiments. In particular, the Majoron self-interaction potential may induce a first order phase transition, producing gravitational waves from bubble collisions. We dubbed such a new scenario {\it violent Majoron model}, because it would be associated to a violent phase transition in the early Universe. Sphaleron constraints can be avoided if the global $U(1)_{B-L}$ is broken at scales lower than the electroweak scale, provided that the B-L spontaneously breaking scale is lower than $10\, {\rm TeV}$ in order to satisfy the cosmological mass density bound. The possibility of a sub-electroweak phase transition is practically unconstrained by cosmological bounds and it may be detected within the sensitivity of next generation of gravitational waves experiments: eLISA, DECIGO and BBO. We also comment on the possible detection in CEPC collider, where Majorons's production can be observed from Higgs' portals in missing transverse energy channels.

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Evaporation and Antievaporation instabilities

We review (anti)evaporation phenomena within the context of quantum gravity and extended theories of gravity. The (anti)evaporation effect is an instability of the black hole horizon discovered in many different scenarios: quantum dilaton-gravity, $f(R)$-gravity, $f(T)$-gravity, string inspired black holes and brane-world cosmology. Evaporating and antievaporating black holes seem to have completely different thermodynamical features compared to standard semiclassical black holes. The purpose of this review is to provide an introduction to conceptual and technical aspects of (anti)evaporation effects, while discussing problems that are still open.

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Super-light baryphotons, Weak Gravity Conjecture and Exotic instantons in Neutron-Antineutron transitions

In companion papers \cite{Addazi:2015pia,Addazi:2016rgo}, we have discussed current bounds of a new super-light baryo-photon, associated to a $U(1)_{B-L}$ gauged, from neutron-antineutron current data, which are competitive with Eötvös type experiments. Here, we discuss the implications of a possible baryo-photon detection in string theory and quantum gravity. The discovery of a very light gauge boson should imply the violation of the Weak Gravity Conjecture, carrying deep consequences in our understanding of holography, quantum gravity and black holes. On the other hand, we show how the detection of a baryo-photon would also exclude the generation of all $B{-}L$ violating operators from Exotic Stringy Instantons. We will disclaim the common statement in literature that neutron-antineutron may indirectly test at least a $300-1000\, \rm TeV$ scale. Searches of baryo-photons can provide indirect informations of the Planck (or String) scale (quantum black holes, holography and non-perturbative stringy effects). This strongly motivates new neutron-antineutron experiments with adjustable magnetic fields dedicated to the detection of super-light baryo-photons.

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Evaporation/Antievaporation and energy conditions in alternative gravity

We discuss the evaporation and antievaporation instabilities of Nariai solution in extended theories of gravity. These phenomena were explicitly shown in several different extensions of General Relativity, suggesting that a universal cause is behind them. We show that evaporation and antievaporation are originated from deformations of energy conditions on the Nariai horizon. Energy conditions get new contributions from the extra propagating degrees of freedom, which can provide extra focalizing or antifocalizing terms in the Raychanduri equation. We also show two explicit examples in $f(R)$-gravity and Gauss-Bonnet gravity.

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A new duality between Topological M-theory and Loop Quantum Gravity

Inspired by the long wave-length limit of topological M-theory, which re-constructs the theory of $3+1$D gravity in the self-dual variables' formulation, we conjecture the existence of a duality between Hilbert spaces, the ${\bf H}$-duality, to unify topological M-theory and loop quantum gravity (LQG). By ${\bf H}$-duality non-trivial gravitational holonomies of the kinematical Hilbert space of LQG correspond to space-like M-branes. The spinfoam approach captures the non-perturbative dynamics of space-like M-branes, and can be claimed to be dual to the S-branes foam. The Hamiltonian constraint dealt with in LQG is reinterpreted as a quantum superposition of SM-brane nucleations and decays.

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Suppression of Bekenstein-Hawking radiation in $f(T)$-gravity

We discuss semiclassical Nariai black holes in the framework of $f(T)$-gravity. For a diagonal choice of tetrades, stable Nariai metrics can be found, emitting Bekenstein-Hawking radiation in semiclassical limit. However, for a non-diagonal choice of tetrades, evaporation and antievaporation instabilities are turned on. In turn, this causes a back-reaction effect suppressing the Bekenstein-Hawking radiation. In particular, evaporation instabilities produce a new radiation -- different by Bekenstein-Hawking emission -- non-violating unitarity in particle physics sector.

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Kac-Moody instantons in space-time foam as an alternative solution to the black hole information paradox

Hawking, Perry and Strominger recently invoked BMS symmetry charges in an attempt to resolve the black hole information paradox. Here we propose an alternative scenario that is based on the Kac-Moody charges. We show that the role of BMS charges can be played by an infinite set of symmetries that emerge from the space-time foam predicted by quantum gravity. Specifically, we focus on Yang-Mills fields embedded in the gravity described by the Holst formulation, and argue that the Yang-Mills and gravitational self-duality conditions in space-time bubbles are related to a new infinite dimensional global symmetry, hidden in the Lagrangian. Such a symmetry is manifested by the Kac-Moody algebra, with zero central charges. This implies the existence, in the space-time foam, of an infinite number of different instantons that are interconnected by the Kac-Moody symmetry. These modes puncture the horizons of the building block of the space-time bubbles. On the other hand, the same Kac-Moody symmetry is retried in non-perturbative regime at the level of the gravitational quantum loops. The new result carries consequences on the no-hair theorem and on the study of quantum black holes. In particular, instantonic moduli of the Kac-Moody charges are quantum hairs encoding the missing black hole information, subtly compatible with the no hair theorem.

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Testing B-violating signatures from Exotic Instantons in future colliders

We discuss possible implications of Exotic Stringy instantons for Baryon-violating signatures in future colliders. In particular, we discuss high-energy quarks collisions and $Λ-\barΛ$ transitions. In principle, $Λ-\barΛ$ process can be probed by high-luminosity electron-positron colliders. However, we find that an extremely high luminosity is needed in order to provide a (somewhat) stringent bound compared to the current data on $NN\rightarrow ππ,KK$. On the other hand, (exotic) instanton-induced six quark interactions can be tested in near future high-energy colliders beyond LHC, at energies around $20-100\, \rm TeV$. Super proton-proton collider (SppC) is capable of such measurement given the proposed energy level of 50-90 TeV. Comparison with other channels is made. In particular, we show the compatibility of our model with neutron-antineutron and $NN\rightarrow ππ,KK$ bounds.

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Evaporation and anti-evaporation instability of a Schwarzschild-de Sitter braneworld: the case of five-dimensional F(R) gravity

We study the problem of a four-dimensional brane lying in the five-dimensional degenerate Schwarzschild-de Sitter (Nariai) black hole, in five-dimensional $F(R)$-gravity. We show that there cannot exist the brane in the Nariai bulk space except the case that the brane tension vanishes. We demonstrate that the five-dimensional Nariai bulk is unstable in a large region of the parameter space. In particular, the Nariai bulk can have classical (anti-)evaporation instabilities. The bulk instability back-reacts on the four-dimensional brane, in case that the brane tension vanishes, and the unstable modes propagate in their world-volume.

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Gravitational waves from dark first order phase transitions and dark photons

Cold Dark Matter particles may interact with ordinary particles through a dark photon, which acquires a mass thanks to a spontaneous symmetry breaking mechanism. We discuss a dark photon model in which the scalar singlet associated to the spontaneous symmetry breaking has an effective potential that induces a first order phase transition in the early Universe. Such a scenario provides a rich phenomenology for electron-positron colliders and gravitational waves interferometers, and may be tested in several different channels. The hidden first order phase transition implies the emission of gravitational waves signals, which may constrain the dark photon's space of parameters. Compared limits from electron-positron colliders, astrophysics, cosmology and future gravitational waves interferometers such as eLISA, U-DECIGO and BBO are discussed. This highly motivates a {\it cross-checking strategy} of data arising from experiments dedicated to gravitational waves, meson factories, the International Linear Collider (ILC), the Circular Electron Positron Collider (CEPC) and other underground direct detection experiments of cold dark matter candidates.

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Dark Matter from Starobinsky Supergravity

We review our recent results on dark matter from Starobinsky supergravity. In this context, a natural candidate for Cold Dark Matter is the gravitino. On the other hand, assuming the supersymmetry broken at scales much higher than the electroweak scale, gravitinos are super heavy particles. In this case, they may be non-thermally produced during inflation, in turn originated by the scalaron field with Starobinsky's potential.Assuming gravitinos as Lightest supersymmetric particles (LSSP), the non-thermal production naturally accounts for the right amount of cold dark matter. Metastability of the gravitino LSSP leads to observable effects of their decay, putting constraints on the corresponding Unstable or Decaying Dark Matters scenarios. In this model, the gravitino mass is controlled by the inflaton field and it runs with it. This implies that a continuous spectrum of superheavy gravitinos is produced during the slow-roll epoch. Implications in phenomenology, model building in GUT scenarios, intersecting D-branes models and instantons in string theories are discussed.

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Energy conditions in Starobinsky supergravity

We consider the classical energy conditions (strong, null and weak) in Starobinsky supergravity theories. We study in detail the simplest Starobinsky supergravity model in the "old-minimal" supergravity setup and find examples of violations of each energy condition for a certain range of the parameters due to extra scalar d.o.f. present in supergravity. We find the null and weak energy conditions to be preserved and the strong energy condition to be violated in the physically relevant examples such as inflation and dark energy.

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Dark Matter and Inflation in $R+ζR^{2}$ Supergravity

As is well known, the gravitational degrees of freedom contained in $R+ζR^{2}$ (super)gravity lead to Starobinsky's potential, in a one-field setting for inflationary Cosmology that appears favored by Planck data. In this letter we discuss another interesting aspect of this model, related to gravitino production, with emphasis on the corresponding mass spectrum. Assuming that supersymmetry is broken at a very high scale, Super Heavy Gravitino Dark Matter (SHGDM) and Starobinsky's inflation can be coherently unified in a $R+ζR^{2}$ supergravity. Gravitinos are assumed to be the Lightest Supersymmetric Particles (LSP) and are non-thermally produced during inflation, in turn originated by a scalar with a Starobinsky's potential. Gravitino mass runs with the inflaton field, so that a continuos spectrum of superheavy gravitinos emerges. The theory is implemented with a $U(1)_{R}$ gauge symmetry. However, in a string UV completion, $U(1)_{R}$-symmetry can be broken by non-perturbative string instantons, while for consistency of our scenario $U(1)_{R}$ gauge symmetry breaking must be broken in order to generate a soft mass terms for the gravitino and gauginos. R-parity violating operators can be generated at non-perturbative level. Gravitinos can decay into very energetic neutrinos and photons in cosmological time scale, with intriguing implications for high energy cosmic rays experiments.

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Dark matter and baryogenesis in the Fermi-bounce curvaton mechanism

We elaborate on a toy-model of matter bounce, in which the matter content is constituted by two fermion species endowed with four fermion interaction term. We describe the curvaton mechanism that is forth generated, and then argue that one of the two fermionic species may realize baryogenesis, while the other (lighter) one is compatible with constrains on extra hot dark matter particles.

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Glimpses of black hole formation/evaporation in highly inelastic, ultra-planckian string collisions

We revisit possible glimpses of black-hole formation by looking at ultra-planckian string-string collisions at very high final-state multiplicity. We compare, in particular, previous results using the optical theorem, the resummation of ladder diagrams at arbitrary loop order, and the AGK cutting rules, with the more recent study of $2 \rightarrow N$ scattering at $N \sim s M_P^{-2} \gg 1$. We argue that some apparent tension between the two approaches disappears once a reinterpretation of the latter's results in terms of suitably defined infrared-safe cross sections is adopted. Under that assumption, the typical final state produced in an ultra-planckian collision does indeed appear to share some properties with those expected from the evaporation of a black hole of mass $\sqrt{s}$, although no sign of thermalization is seen to emerge at this level of approximation.

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