33,385 research outputs found
Quantum Gravity Effects around Sagittarius A*
Recent VLBI observations have resolved Sagittarius A* at horizon scales. The
Event Horizon Telescope is expected to provide increasingly good images of the
region around the Schwarzschild radius of Sgr A* soon. A number of
authors have recently pointed out the possibility that non-perturbative quantum
gravitational phenomena could affect the space surrounding a black hole. Here
we point out that the existence of a region around where these
effects should be maximal.Comment: 5 pages; Received honorable mention in the Gravity Research
Foundation 2016 Awards for Essays on Gravitatio
Death and resurrection of the zeroth principle of thermodynamics
The zeroth principle of thermodynamics in the form "temperature is uniform at
equilibrium" is notoriously violated in relativistic gravity. Temperature
uniformity is often derived from the maximization of the total number of
microstates of two interacting systems under energy exchanges. Here we discuss
a generalized version of this derivation, based on informational notions, which
remains valid in the general context. The result is based on the observation
that the time taken by any system to move to a distinguishable (nearly
orthogonal) quantum state is a universal quantity that depends solely on the
temperature. At equilibrium the net information flow between two systems must
vanish, and this happens when two systems transit the same number of
distinguishable states in the course of their interaction.Comment: 5 pages, 2 figure
Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling
We show that there is a classical metric satisfying the Einstein equations
outside a finite spacetime region where matter collapses into a black hole and
then emerges from a white hole. We compute this metric explicitly. We show how
quantum theory determines the (long) time for the process to happen. A black
hole can thus quantum-tunnel into a white hole. For this to happen, quantum
gravity should affect the metric also in a small region outside the horizon: we
show that contrary to what is commonly assumed, this is not forbidden by
causality or by the semiclassical approximation, because quantum effects can
pile up over a long time. This scenario alters radically the discussion on the
black hole information puzzle.Comment: 10 pages, 5 figure
Drift Correction Methods for gas Chemical Sensors in Artificial Olfaction Systems: Techniques and Challenges
In this chapter the authors introduce the main challenges faced when developing drift correction techniques and will propose a deep overview of state-of-the-art methodologies that have been proposed in the scientific literature trying to underlying pros and cons of these techniques and focusing on challenges still open and waiting for solution
Emergent Higgsless Superconductivity
We present a new Higgsless model of superconductivity, inspired from anyon
superconductivity but P- and T-invariant and generalizable to any dimension.
While the original anyon superconductivity mechanism was based on
incompressible quantum Hall fluids as average field states, our mechanism
involves topological insulators as average field states. In D space dimensions
it involves a (D-1)-form fictitious pseudovector gauge field which originates
from the condensation of topological defects in compact low-energy effective BF
theories. There is no massive Higgs scalar as there is no local order
parameter. When electromagnetism is switched on, the photon acquires mass by
the topological BF mechanism. Although the charge of the gapless mode (2) and
the topological order (4) are the same as those of the standard Higgs model,
the two models of superconductivity are clearly different since the origins of
the gap, reflected in the high-energy sectors are totally different. In 2D this
type of superconductivity is explicitly realized as global superconductivity in
Josephson junction arrays. In 3D this model predicts a possible phase
transition from topological insulators to Higgsless superconductors.Comment: Prepared for the proceedings of the XII Quark Confinement and the
Hadron Spectrum, 29 August to 3 September 2016, Thessaloniki, Greece. arXiv
admin note: substantial text overlap with arXiv:1408.506
- …