On Loop Quantum Gravity Phenomenology and the Issue of Lorentz Invariance

A simple model is constructed which allows to compute modified dispersion relations with effects from loop quantum gravity. Different quantization choices can be realized and their effects on the order of corrections studied explicitly. A comparison with more involved semiclassical techniques shows that there is agreement even at a quantitative level. Furthermore, by contrasting Hamiltonian and Lagrangian descriptions we show that possible Lorentz symmetry violations may be blurred as an artifact of the approximation scheme. Whether this is the case in a purely Hamiltonian analysis can be resolved by an improvement in the effective semiclassical analysis.Comment: 16 pages, RevTeX

Controlled nucleation of topological defects in the stripe domain patterns of Lateral multilayers with Perpendicular Magnetic Anisotropy: competition between magnetostatic, exchange and misfit interactions

Magnetic lateral multilayers have been fabricated on weak perpendicular magnetic anisotropy amorphous Nd-Co films in order to perform a systematic study on the conditions for controlled nucleation of topological defects within their magnetic stripe domain pattern. A lateral thickness modulation of period $w$ is defined on the nanostructured samples that, in turn, induces a lateral modulation of both magnetic stripe domain periods $\lambda$ and average in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer period and in-plane applied field, thin and thick regions switch independently during in-plane magnetization reversal and domain walls are created within the in-plane magnetization configuration coupled to variable angle grain boundaries and disclinations within the magnetic stripe domain patterns. This process is mainly driven by the competition between rotatable anisotropy (that couples the magnetic stripe pattern to in-plane magnetization) and in-plane shape anisotropy induced by the periodic thickness modulation. However, as the structural period $w$ becomes comparable to magnetic stripe period $\lambda$, the nucleation of topological defects at the interfaces between thin and thick regions is hindered by a size effect and stripe domains in the different thickness regions become strongly coupled.Comment: 10 pages, 7 figures, submitted to Physical Review

Drell-Yan bounds on gapped continuum spectra

Theories with gapped continuum spectra have gotten some attention, either as pure 4D models like unparticles, or in 5D realizations as certain soft walls constructions. In this paper, we derive experimental bounds from Drell-Yan processes (pp → ℓ+ℓ−, pp → ℓ±ν) in a particular scenario where the electroweak bosons propagate in an extra dimension that produces a propagator with a continuum spectrum, on top of the isolated corresponding Standard Model pole. Using current LHC data we put a lower bound on the gap of 4.2 TeV (expected), 6.2 TeV (observed, bins with < 10 events combined) at 95% CL, with some dependence in the observed limit on how low statistics bins are treated. We also study the limits for HL-LHC.Atraccion de Talento program (Modalidad 1) of the Comunidad de Madrid (Spain) 2019-T1/TIC-14019Spanish Research Agency (Agencia Estatal de Investigacion) CEX2020-001007-S PID2021-124704NB-I00MCIN/AEIGerman Research Foundation (DFG) A-FQM-178-UGR18FSE Investing in your futureFEDER/Junta de Andalucia - Consejeria de Economia y Conocimiento FQM-225Junta de Andalucia 2021 SGR 00649Ramon y Cajal Program of the University of GranadaGeneralitat de Catalunya PID2020-115845GB-I00Spanish Government PHY-2112540National Science Foundation (NSF)CERCA program of the Generalitat de CatalunyaConsejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET)ANPCyT PICT 2018-03682 PID2020-114767GB-I00 RYC-2016-20678 PICT-2021-0037

Discriminación de bosques de Araucaria araucana en el Parque Nacional Conguillío, centro-sur de Chile, mediante datos Landsat TM

Martin, JS (San Martin, Jose). Univ Talca, Inst Biol Vegetal & Biotecnol, Talca, ChileAraucaria forests (Araucaria araucana) have a tremendous ecological relevance; however, the information concerning their spatial distribution is still insufficient. They have only been classified according to small management scales, using satellite photos and images processed through conventional methods. The present study had as its objective to discriminate and characterize types of A. araucana forests in the Conguillio National Park, located in the Southern-Center Chile, through data derived from the Landsat-5 TM satellite and geographic information systems. The normalized difference vegetation index (NDVI) was satisfactorily related with variables corresponding to crown coverage and the diameter at breast height; thus, these index values were incorporated to the classification process. Using the digital elevation model and the NDVI, the effect provoked by the shadow was minimized. Seven types of forests, between dense and semi-dense-open, were discriminated in accordance with the accompanying species. The global reliability of the classification was 83.8 %. The greatest reliability for the producer was for the medium crown density forest of A. araucana - N. dombeyi (B1) (87.5 %); and for the consumer, for the high crown density forests of A. araucana - N. dombeyi (B1) and also for those of medium density (B2) (93 %). It is concluded that incorporating NDVI values and data derived from the digital elevation model to the satellite classification process, it is possible to discriminate araucaria forests with satisfactory reliability in areas of rough relief, which is very useful information for the management of these forestry ecosystems

Free energy methods in Coupled Electron Ion Monte Carlo

Recent progress in simulation methodologies and in computer power allow first principle simulations of condensed systems with Born-Oppenheimer electronic energies obtained by Quantum Monte Carlo methods. Computing free energies and therefore getting a quantitative determination of phase diagrams is one step more demanding in terms of computer resources. In this paper we derive a general relation to compute the free energy of an ab-initio model with Reptation Quantum Monte Carlo (RQMC) energies from the knowledge of the free energy of the same ab-initio model in which the electronic energies are computed by the less demanding but less accurate Variational Monte Carlo (VMC) method. Moreover we devise a procedure to correct transition lines based on the use of the new relation. In order to illustrate the procedure, we consider the liquid-liquid phase transition in hydrogen, a first order transition between a lower pressure, molecular and insulating phase and a higher pressure, partially dissociated and conducting phase. We provide new results along the T = 600K isotherm across the phase transition and find good agreement between the transition pressure and specific volumes at coexistence for the model with RQMC accuracy between the prediction of our procedure and the values that can be directly inferred from the observed plateau in the pressure-volume curve along the isotherm. This work paves the way for future use of VMC in first principle simulations of high pressure hydrogen, an essential simplification when considering larger system sizes or quantum proton effects by Path Integral Monte Carlo methods.Comment: Accepted for publication in Molecular Physic

The Berry phase in inflationary cosmology

We derive an analogue of the Berry phase associated with inflationary cosmological perturbations of quantum mechanical origin by obtaining the corresponding wavefunction. We have further shown that cosmological Berry phase can be completely envisioned through the observable parameters, viz. spectral indices. Finally, physical significance of this phase is discussed from the point of view of theoretical and observational aspects with some possible consequences of this quantity in inflationary cosmology.Comment: 9 pages, Modified version to appear in Classical and Quantum Gravity. arXiv admin note: text overlap with arXiv:quant-ph/0307084 by other author

Asymptotic Properties of Difference Equations for Isotropic Loop Quantum Cosmology

In loop quantum cosmology, a difference equation for the wave function describes the evolution of a universe model. This is different from the differential equations that arise in Wheeler-DeWitt quantizations, and some aspects of general properties of solutions can appear differently. Properties of particular interest are boundedness and the presence of small-scale oscillations. Continued fraction techniques are used to show in different matter models the presence of special initial conditions leading to bounded solutions, and an explicit expression for these initial values is derived.Comment: 27 pages, 2 figure

Trial wave functions for High-Pressure Metallic Hydrogen

Many body trial wave functions are the key ingredient for accurate Quantum Monte Carlo estimates of total electronic energies in many electron systems. In the Coupled Electron-Ion Monte Carlo method, the accuracy of the trial function must be conjugated with the efficiency of its evaluation. We report recent progress in trial wave functions for metallic hydrogen implemented in the Coupled Electron-Ion Monte Carlo method. We describe and characterize several types of trial functions of increasing complexity in the range of the coupling parameter $1.0 \leq r_s \leq1.55$. We report wave function comparisons for disordered protonic configurations and preliminary results for thermal averages.Comment: 11 pages, 6 figures, submitted to Computer Physics Communication

Degenerate Configurations, Singularities and the Non-Abelian Nature of Loop Quantum Gravity

Degenerate geometrical configurations in quantum gravity are important to understand if the fate of classical singularities is to be revealed. However, not all degenerate configurations arise on an equal footing, and one must take into account dynamical aspects when interpreting results: While there are many degenerate spatial metrics, not all of them are approached along the dynamical evolution of general relativity or a candidate theory for quantum gravity. For loop quantum gravity, relevant properties and steps in an analysis are summarized and evaluated critically with the currently available information, also elucidating the role of degrees of freedom captured in the sector provided by loop quantum cosmology. This allows an outlook on how singularity removal might be analyzed in a general setting and also in the full theory. The general mechanism of loop quantum cosmology will be shown to be insensitive to recently observed unbounded behavior of inverse volume in the full theory. Moreover, significant features of this unboundedness are not a consequence of inhomogeneities but of non-Abelian effects which can also be included in homogeneous models.Comment: 28 pages, 1 figure; v2: extended discussion of singularity removal and summar