arXiv subjects

Octavian Micu

Publications and source records attributed to Octavian Micu.

33 records · Page 2Linked to original sources

arXiv2014

Black holes as self-sustained quantum states, and Hawking radiation

We employ the recently proposed formalism of the "horizon wave-function" to investigate the emergence of a horizon in models of black holes as Bose-Einstein condensates of gravitons. We start from the Klein-Gordon equation for a massless scalar (toy graviton) field coupled to a static matter current. The (spherically symmetric) classical field reproduces the Newtonian potential generated by the matter source, and the corresponding quantum state is given by a coherent superposition of scalar modes with continuous occupation number. Assuming an attractive self-interaction that allows for bound states, one finds that (approximately) only one mode is allowed, and the system can be confined in a region of the size of the Schwarzschild radius. This radius is then shown to correspond to a proper horizon, by means of the horizon wave-function of the quantum system, with an uncertainty in size naturally related to the expected typical energy of Hawking modes. In particular, this uncertainty decreases for larger black hole mass (with larger number of light scalar quanta), in agreement with semiclassical expectations, a result which does not hold for a single very massive particle. We finally speculate that a phase transition should occur during the gravitational collapse of a star, ideally represented by a static matter current and Newtonian potential, that leads to a black hole, again ideally represented by the condensate of toy gravitons, and suggest an effective order parameter that could be used to investigate this transition.

hep-th↗

arXiv2014

Quantum Black Holes Effects on the Shape of Extensive Air Showers

We investigate the possibility to find a characteristic TeV scale quantum black holes decay signature in the data recorded by cosmic rays experiments. TeV black holes can be produced via the collisions of ultra high energetic protons (E > $10^18$ eV) with nucleons the from atmosphere. We focus on the case when the black holes decay into two particles moving in the forward direction in the Earth reference frame (back-to-back in the center of mass reference frame) and induce two overlapping showers. When reconstructing both the energy and the shape of the resultant air shower, there is a significant difference between showers induced only via standard model interactions and showers produced via the back-to-back decay of black holes as intermediate states.

hep-ph↗

arXiv2014

Minimum length effects in black hole physics

We review the main consequences of the possible existence of a minimum measurable length, of the order of the Planck scale, on quantum effects occurring in black hole physics. In particular, we focus on the ensuing minimum mass for black holes and how modified dispersion relations affect the Hawking decay, both in four space-time dimensions and in models with extra spatial dimensions. In the latter case, we briefly discuss possible phenomenological signatures.

hep-th↗

arXiv2014

Quantum hoop conjecture: Black hole formation by particle collisions

We address the issue of (quantum) black hole formation by particle collision in quantum physics. We start by constructing the horizon wave-function for quantum mechanical states representing two highly boosted non-interacting particles that collide in flat one-dimensional space. From this wave-function, we then derive a probability that the system becomes a black hole as a function of the initial momenta and spatial separation between the particles. This probability allows us to extend the hoop conjecture to quantum mechanics and estimate corrections to its classical counterpart.

hep-th↗

arXiv2014

Back-to-Back Black Holes decay Signature at Neutrino Observatories

We propose a decay signature for non-thermal small black holes with masses in the TeV range which can be discovered by neutrino observatories. The black holes would result due to the impact between ultra high energy neutrinos with nuclei in water or ice and decay instantaneously. They could be produced if the Planck scale is in the few TeV region and the highly energetic fluxes are large enough. Having masses close to the Planck scale, the typical decay mode for these black holes is into two particles emitted back-to-back. For a certain range of angles between the emitted particles and the center of mass direction of motion, it is possible for the detectors to measure separate muons having specific energies and their trajectories oriented at a large enough angle to prove that they are the result of a back-to-back decay event.

hep-ph↗

arXiv2012

Quantum Black Holes from Cosmic Rays

We investigate the possibility for cosmic ray experiments to discover non-thermal small black holes with masses in the TeV range. Such black holes would result due to the impact between ultra high energy cosmic rays or neutrinos with nuclei from the upper atmosphere and decay instantaneously. They could be produced copiously if the Planck scale is in the few TeV region. As their masses are close to the Planck scale, these holes would typically decay into two particles emitted back-to-back. Depending on the angles between the emitted particles with respect to the center of mass direction of motion, it is possible for the simultaneous showers to be measured by the detectors.

hep-ph↗

arXiv2011

Lepton number violating effects in neutrino oscillations

We develop a non-adiabatic perturbation theory for oscillations involving an arbitrary number of neutrino and antineutrino species, including the possibility of lepton number violation which we treat as a small effect. We interpret the physics of such an approach for the one generation case by introducing the notion of adiabaticity for neutrino and antineutrino oscillations in analogy to flavor oscillations. We find that in a CP-odd matter environment a small lepton number violation in vacuo can be enhanced. Eventually, we apply the perturbation theory to the two generation case and work out an example for manifestations of lepton number violation, which can be solved both perturbatively as well as analytically thereby further clarifying the nature of the perturbation expansion.

hep-ph↗

arXiv2010

Affect of brane thickness on microscopic tidal-charged black holes

We study the phenomenological implications stemming from the dependence of the tidal charge on the brane thickness $L$ for the evaporation and decay of microscopic black holes. In general, the larger $L$, the longer are the black hole life-times and the greater their maximum mass for those cases in which the black hole can grow. In particular, we again find that tidal-charged black holes might live long enough to escape the detectors and even the gravitational field of the Earth, thus resulting in large amounts of missing energy. However, under no circumstances could TeV-scale black holes grow enough to enter the regime of Bondi accretion.

hep-ph↗

arXiv2010

Theoretical survey of tidal-charged black holes at the LHC

We analyse a family of brane-world black holes which solve the effective four-dimensional Einstein equations for a wide range of parameters related to the unknown bulk/brane physics. We first constrain the parameters using known experimental bounds and, for the allowed cases, perform a numerical analysis of their time evolution, which includes accretion through the Earth. The study is aimed at predicting the typical behavior one can expect if such black holes were produced at the LHC. Most notably, we find that, under no circumstances, would the black holes reach the (hazardous) regime of Bondi accretion. Nonetheless, the possibility remains that black holes live long enough to escape from the accelerator (and even from the Earth's gravitational field) and result in missing energy from the detectors.

hep-th↗

arXiv2009

Explaining LSND and MiniBooNE using altered neutrino dispersion relations

We investigate the possibility to explain the MiniBooNE anomaly by CPT and Lorentz symmetry violating neutrino-antineutrino oscillations in a two generation framework. We work with four non-zero CPT-violating parameters that allow for resonant enhancements in neutrino-antineutrino oscillation phenomena in vacuo which are suitably described in terms of charge conjugation eigenstates of the system. We study the relation between the flavor, charge conjugation and mass eigenbasis of neutrino-antineutrino oscillations and examine the interplay between the available CPT-violating parameter space and possible resonance structures.

hep-ph↗

arXiv2009

Explaining LSND using extra-dimensional shortcuts

We explore the possibility to explain the LSND result in the context of extra-dimensional theories. If sterile neutrinos take shortcuts through extra dimensions, this results in altered neutrino dispersion relations. Active-sterile neutrino oscillations thus are modified and new types of resonances occur.

hep-ph↗

arXiv2009

Neutrino-antineutrino oscillations as a possible solution for the LSND and MiniBooNE anomalies?

We investigate resonance structures in CPT and Lorentz symmetry violating neutrino-antineutrino oscillations in a two generation framework. We work with four non-zero CPT-violating parameters that allow for resonant enhancements in neutrino-antineutrino oscillation phenomena in vacuo which are suitably described in terms of charge conjugation eigenstates of the system. We study the relation between the flavor, charge conjugation and mass eigenbasis of neutrino-antineutrino oscillations and examine the interplay between the available CPT-violating parameter space and possible resonance structures. Eventually we remark on the consequences of such scenarios for neutrino oscillation experiments, namely possible solutions for the LSND and MiniBooNE anomalies.

hep-ph↗

arXiv2009

Baseline-dependent neutrino oscillations with extra-dimensional shortcuts

In extra-dimensional scenarios oscillations between active and sterile neutrinos can be governed by a new resonance in the oscillation amplitude. This resonance results when cancelation occurs between two phase differences, the usual kinematic one coming from the neutrino mass-squared difference, and a geometric one coming from the difference in travel times of the sterile neutrino through the bulk relative to the active neutrino confined to the brane. In this work we introduce a specific metric for the brane-bulk system, from which we explicitly derive extra-dimensional geodesics for the sterile neutrino, and ultimately the oscillation probability of the active-sterile two-state system. We find that for an asymmetrically-warped metric, the resonance condition involves both the neutrino energy E and the travel distance L on the brane. In other words, the resonant energy may be viewed as baseline-dependent. We show that to a good approximation, the resonance condition is not on E or on L, but rather on the product LE. The model is rich in implications, including the possibility of multiple solutions to the resonance condition, with ramifications for existing data sets, e.g., LSND and MiniBooNE. Some phenomenology with these brane-bulk resonances is discussed.

hep-ph↗

arXiv2007

Boundaries and the Casimir effect in non-commutative space-time

We calculate modifications to the scalar Casimir force between two parallel plates due to space-time non-commutativity. We devise a heuristic approach to overcome the difficulties of describing boundaries in non-commutative theories and predict that boundary corrections are of the same order as non-commutative volume corrections. Further, both corrections have the form of more conventional finite surface effects.

hep-th↗

arXiv2002

Microscopic Black Holes as a Source of Ultrahigh Energy gamma-rays

We investigate the idea that ultrahigh energy gamma-rays (E>10 TeV) can be produced when charged particles are accelerated by microscopic black holes. We begin by showing that microscopic black holes may exist as remnants of primordial black holes or as products of the collisions in the large extra dimensions scenario of high energy cosmic rays with atmospheric particles. We then solve Maxwell's equations on curved spacetime backgrounds in 4, 5 and 6 dimensions and use the solutions to calculate the energy distributions. From the latter we obtain the black hole parameters needed to produce the energies of the observed gamma-rays.

astro-ph↗