Naturalness in emergent spacetime

Effective field theories (EFTs) have been widely used as a framework in order to place constraints on the Planck suppressed Lorentz violations predicted by various models of quantum gravity. There are however technical problems in the EFT framework when it comes to ensuring that small Lorentz violations remain small -- this is the essence of the "naturalness" problem. Herein we present an "emergent" space-time model, based on the "analogue gravity'' programme, by investigating a specific condensed-matter system that is in principle capable of simulating the salient features of an EFT framework with Lorentz violations. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. Furthermore our model explicitly avoids the "naturalness problem", and makes specific suggestions regarding how to construct a physically reasonable quantum gravity phenomenology.Comment: V1:4 pages, revtex4; V2: slight changes in title, presentation, and conclusions. This version to appear in Physical Review Letter

Iron fluorescence from within the innermost stable orbit of black hole accretion disks

The fluorescent iron Ka line is a powerful observational probe of the inner regions of black holes accretion disks. Previous studies have assumed that only material outside the radius of marginal stability can contribute to the observed line emission. Here, we show that fluorescence by material inside the radius of marginal stability, which is in the process of spiralling towards the event horizon, can have a observable influence on the iron line profile and equivalent width. For concreteness, we consider the case of a geometrically thin accretion disk, around a Schwarzschild black hole, in which fluorescence is excited by an X-ray source placed at some height above the disk and on the axis of the disk. Fully relativistic line profiles are presented for various source heights and efficiencies. It is found that the extra line flux generally emerges in the extreme red wing of the iron line, due to the large gravitational redshift experienced by photons from the region within the radius of marginal stability. We apply our models to the variable iron line seen in the ASCA spectrum of the Seyfert nucleus MCG-6-30-15. It is found that the change in the line profile, equivalent width, and continuum normalization, can be well explained as being due to a change in the height of the source above the disk. We discuss the implications of these results for distinguishing rapidly-rotating black holes from slowly rotating holes using iron line diagnostics.Comment: 20 pages, LaTeX. Accepted for publication in Astrophysical Journal. Figures 3 to 7 replaced with corrected versions (previous figures affected by calculational error). Some changes in the best fitting parameter

Time-reversible Born-Oppenheimer molecular dynamics

We present a time-reversible Born-Oppenheimer molecular dynamics scheme, based on self-consistent Hartree-Fock or density functional theory, where both the nuclear and the electronic degrees of freedom are propagated in time. We show how a time-reversible adiabatic propagation of the electronic degrees of freedom is possible despite the non-linearity and incompleteness of the self-consistent field procedure. Time-reversal symmetry excludes a systematic long-term energy drift for a microcanonical ensemble and the number of self-consistency cycles can be kept low (often only 2-4 cycles per nuclear time step) thanks to a good initial guess given by the adiabatic propagation of the electronic degrees of freedom. The time-reversible Born-Oppenheimer molecular dynamics scheme therefore combines a low computational cost with a physically correct time-reversible representation of the dynamics, which preserves a detailed balance between propagation forwards and backwards in time.Comment: 4 pages, 4 figure

Wave Equation for Sound in Fluids with Vorticity

We use Clebsch potentials and an action principle to derive a closed system of gauge invariant equations for sound superposed on a general background flow. Our system reduces to the Unruh (1981) and Pierce (1990) wave equations when the flow is irrotational, or slowly varying. We illustrate our formalism by applying it to waves propagating in a uniformly rotating fluid where the sound modes hybridize with inertial waves.Comment: RevTeX, 27page

Tolman mass, generalized surface gravity, and entropy bounds

In any static spacetime the quasi-local Tolman mass contained within a volume can be reduced to a Gauss-like surface integral involving the flux of a suitably defined generalized surface gravity. By introducing some basic thermodynamics and invoking the Unruh effect one can then develop elementary bounds on the quasi-local entropy that are very similar in spirit to the holographic bound, and closely related to entanglement entropy.Comment: V1: 4 pages. Uses revtex4-1; V2: Three references added; V3: Some notational changes for clarity; introductory paragraph rewritten; no physics changes. This version accepted for publication in Physical Review Letter

Fe K\alpha emission from photoionized slabs: the impact of the iron abundance

Iron K\alpha emission from photoionized and optically thick material is observed in a variety of astrophysical environments including X-ray binaries, active galactic nuclei, and possibly gamma-ray bursts. This paper presents calculations showing how the equivalent width (EW) of the Fe K line depends on the iron abundance of the illuminated gas and its ionization state -- two variables subject to significant cosmic scatter. Reflection spectra from a constant density slab which is illuminated with a power-law spectrum with photon-index \Gamma are computed using the code of Ross & Fabian. When the Fe K EW is measured from the reflection spectra alone, we find that it can reach values greater than 6 keV if the Fe abundance is about 10 times solar and the illuminated gas is neutral. EWs of about 1 keV are obtained when the gas is ionized. In contrast, when the EW is measured from the incident+reflected spectrum, the largest EWs are ~800 keV and are found when the gas is ionized. When \Gamma is increased, the Fe K line generally weakens, but significant emission can persist to larger ionization parameters. The iron abundance has its greatest impact on the EW when it is less than 5 times solar. When the abundance is further increased, the line strengthens only marginally. Therefore, we conclude that Fe K lines with EWs much greater than 800 eV are unlikely to be produced by gas with a supersolar Fe abundance. These results should be useful in interpreting Fe K emission whenever it arises from optically thick fluorescence.Comment: 5 pages, 5 figures, accepted by MNRAS Letter

THE IFC FILE FORMAT AS A MEANS OF INTEGRATING BIM AND GIS: THE CASE OF THE MANAGEMENT AND MAINTENANCE OF UNDERGROUND NETWORKS

Abstract. The construction sector is undergoing an important digital revolution. The integration between Building Information Modeling (BIM) and Geographical Information System (GIS) is a key component of this revolution and is increasingly discussed. Although benefits are already recognised, several challenges still remain. The purpose of this paper is to present the method proposed by the GEOBIMM project to overcome the existing barriers towards the integration between BIM and GIS domains and to present the first results applied to the maintenance of underground networks. The results are a set of guidelines essential for the integration of BIM files in GIS platforms within the GEOBIMM domain, to ensure: the appropriate geometric description of the elements; the correct georeferencing; the geospatial semantic and topological interoperability between the two systems; the appropriate definition of the information parameters. These pillars are further used to develop a guideline for planners and construction companies supporting them in developing compliant BIM models

Elementary analysis of the special relativistic combination of velocities, Wigner rotation, and Thomas precession

The purpose of this paper is to provide an elementary introduction to the qualitative and quantitative results of velocity combination in special relativity, including the Wigner rotation and Thomas precession. We utilize only the most familiar tools of special relativity, in arguments presented at three differing levels: (1) utterly elementary, which will suit a first course in relativity; (2) intermediate, to suit a second course; and (3) advanced, to suit higher level students. We then give a summary of useful results, and suggest further reading in this often obscure field.Comment: V1: 25 pages, 6 figures; V2: 22 pages, 5 figures. The revised version is shortened and the arguments streamlined. Minor changes in notation and figures. This version matches the published versio

The impact and correlation of the digital transformation on GDP growth in different regions Worldwide

[EN] Currently our society is experiencing a process of digital transfor- mation worldwide, in 2016 the digital economy accounted for 22.5% of the world economy. The digital transformation has enabled the creation of new business models, the generation of opportunities and the maximization of effi- ciency in traditional companies that have wanted to reconvert their business model towards a new digital environment and the culture of data orientation. This document contains an analysis of how the adoption of digital technologies has a positive influence on the growth of the world economy as a whole, and particularly on the growth of some regions of the world

Pentacene in 1,3,5-Tri(1-naphtyl)benzene: A Novel Standard for Transient EPR Spectroscopy at Room Temperature

Testing and calibrating an experimental setup with standard samples is an essential aspect of scientific research. Single crystals of pentacene in p-terphenyl are widely used for this purpose in transient electron paramagnetic resonance (EPR) spectroscopy. However, this sample is not without downsides: the crystals need to be grown and the EPR transitions only appear at particular orientations of the crystal with respect to the external magnetic field. An alternative host for pentacene is the glass-forming 1,3,5-tri(1-naphtyl)benzene (TNB). Due to the high glass transition point of TNB, an amorphous glass containing randomly oriented pentacene molecules is obtained at room temperature. Here we demonstrate that pentacene dissolved in TNB gives a typical “powder-like” transient EPR spectrum of the triplet state following pulsed laser excitation. From the two-dimensional data set, it is straightforward to obtain the zero-field splitting parameters and relative populations by spectral simulation as well as the B1 field in the microwave resonator. Due to the simplicity of preparation, handling and stability, this system is ideal for adjusting the laser beam with respect to the microwave resonator and for introducing students to transient EPR spectroscopy