A new approach to the study of lightlike manifolds

Proponemos un nuevo enfoque al estudio de las subvariedades luz, cuyo estudio hasta el momento dependía de una elección arbitraria de una distribución pantalla que hacía completamente inadecuado el estudio de la geometría intrínseca. Las técnicas utilizarán geometrías de Cartan.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Conjugate Points along lightlike geodesics of Lorentzian manifolds

En esta charla se muestran algunas propiedades que relacionan la distribución de los puntos conjugados en las geodésicas luz con propiedades globales tanto geométricas como topológicas de la variedad. Los resultados expuestos se aplican al estudio de las esferas de dimensión impar

Mean curvature of spacelike submanifolds in a Brinkmann spacetime

Several geometric properties of complete spacelike submanifolds, with codimension at least two, in a Brinkmann spacetime are shown from natural assumptions involving the mean curvature vector field \mcv of the spacelike submanifold. Especially, we get sufficient conditions that assure that a spacelike submanifold is contained in a leaf of the foliation of the Brinkmann spacetime defined by the orthogonal vectors to the parallel lightlike vector field. When this vector field is the gradient of a smooth function, a characterization of arbitrary codimension spacelike submanifolds contained in a leaf of this foliation is given. In the case of plane fronted wave spacetimes, relevant examples of Brinkmann spacetimes that generalize pp-waves spacetimes, several uniqueness results for codimension two spacelike submanifolds are obtained. In particular, it is proven that any compact codimension two spacelike submanifold with \mcv=0 in a plane fronted spacetime wave must be a (totally geodesic) front of wave.The first author has been partially supported by MINECO/FEDER project MTM2015-65430-P, Fundaci\'on S\'eneca project 19901/GERM/15 and research grant 19783/FPI/15 from Fundaci\'on S\'eneca, the second and the third authors by Spanish MINECO and ERDF project MTM2016-78807-C2-1-P and Andalusian and ERDF project A-FQM-494-UGR1

Rigidity results for complete spacelike submanifolds in plane fronted waves

New rigidity results for complete non-compact spacelike submanifolds of arbitrary codimension in plane fronted waves are obtained. Under appropriate assumptions, we prove that a complete spacelike submanifold in these spacetimes is contained in a characteristic lightlike hypersurface. Moreover, for a complete codimension two extremal submanifold in a plane fronted wave we show sufficient conditions to guarantee that it is a (totally geodesic) wavefront.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Funding for open access charge: Universidad de Málaga / CBU

Role of phosphorus on activated carbons used as catalytic support in steam reforming of pyrolysis liquids

Hydrogen production from steam reforming (SR) of the liquids resulting from biomass waste pyrolysis with nickel catalysts is a sustainable alternative for decarbonization. Chemical activation with H3PO4 provide activated carbons (ACs) with high surface area and porosity development, improved surface oxidation/gasification resistance and acid character due to the presence of stable surface phosphorus groups. In addition, they can be prepared from the same biomass waste making them sustainable supports for steam reforming Ni catalysts. However, little is known about the role of surface P groups on the activity of nickel. In this work ACs, with different amounts of P, have been used as support for steam reforming Ni catalysts in order to study the effect of P on the catalytic activity and stability. Pistachio shell (PS), a non-edible agroforestry waste, has been used as feedstock for both the preparation of the activated carbons (ACs) and the pyrolysis liquids. P-containing AC was obtained by chemical activation of PS with 3:1 acid to precursor mass ratio and activation temperature of 500 ºC (PS3P sample). The amount of surface P in PS3P was partially decreased by hydrogen treatment at 600 ºC for 4 h (PSLP sample). P-free AC was also prepared by CO2 physical activation of PS at 800 ºC for 3 h (PSG sample). 10 % wt. Ni nominal loading were supported onto the ACs by the incipient wetness impregnation method with Ni(NO3)2·6H2O and thermal annealing in N2 atmosphere at 700 ºC for 2 h. The resulting catalysts have been evaluated on SR of a mixture of oxygenated hydrocarbons (ethanol, acetone and acetic acid) usually found in pyrolysis liquids. Each of them was fed with a 0.75 % volume concentration, while the steam to carbon ratio was set on the stoichiometric value. The reaction was carried out in a fixed bed tubular reactor at a temperature ranging from 500 to 800 °C and using a space time of 50 gcat·s·mmol-1.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Los autores agradecen al MICCIN (RTI2018-097555-B-100) por la ayuda financiera

Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at √s = 13 TeV

Abstract The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d̂ t) and chromomagnetic (μ̂ t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable AFB(1) is used to approximate the asymmetry. Candidate t t ¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t t ¯ final states. The values found for the parameters are AFB(1)=0.048−0.087+0.095(stat)−0.029+0.020(syst),μ̂t=−0.024−0.009+0.013(stat)−0.011+0.016(syst), and a limit is placed on the magnitude of | d̂ t| < 0.03 at 95% confidence level. [Figure not available: see fulltext.

Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV

MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Measurement of prompt open-charm production cross sections in proton-proton collisions at root s=13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb(-1). The differential production cross sections of the D*(+/-), D-+/-, and D-0 ((D) over bar (0)) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < p(T) < 100 GeV and vertical bar eta vertical bar < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.Peer reviewe