Asenjo, F. A., & Hojman, S. A. (2023). Time-domain supersymmetry for massless scalar and electromagnetic fields in anisotropic cosmologies. Phys. Scr., 98(10), 105302.
Abstract: It is shown that any cosmological anisotropic model produces supersymmetric theories for both massless scalar and electromagnetic (abelian) fields. This supersymmetric theory is the time-domain analogue of a supersymmetric quantum mechanics algebra theory. In this case, the variations of the anisotropic scale factors of the Universe are responsible for triggering the supersymmetry. For scalar fields, the superpartner fields evolve in two different cosmological scenarios (Universes). On the other hand, for propagating electromagnetic fields, supersymmetry is manifested through its polarization degrees of freedom in one Universe. In this case, polarization degrees of freedom of electromagnetic waves, which are orthogonal to its propagation direction, become superpartners from each other. This behavior can be measured, for example, through the rotation of the plane of polarization of cosmological light.
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Berkovits, N., & Chandia, O. (2014). Simplified pure spinor b ghost in a curved heterotic superstring background. J. High Energy Phys., (6), 12 pp.
Abstract: Using the RNS-like fermionic vector variables introduced in arXiv:1305.0693, the pure spinor b ghost in a curved heterotic superstring background is easily constructed. This construction simplifies and completes the b ghost construction in a curved background of arXiv:1311.7012.
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Bevilacqua, M., Caamano-Carrillo, C., Arellano-Valle, R. B., & Gomez, C. (2022). A class of random fields with two-piece marginal distributions for modeling point-referenced data with spatial outliers. Test, 31(3), 644–674.
Abstract: In this paper, we propose a new class of non-Gaussian random fields named two-piece random fields. The proposed class allows to generate random fields that have flexible marginal distributions, possibly skewed and/or heavy-tailed and, as a consequence, has a wide range of applications. We study the second-order properties of this class and provide analytical expressions for the bivariate distribution and the associated correlation functions. We exemplify our general construction by studying two examples: two-piece Gaussian and two-piece Tukey-h random fields. An interesting feature of the proposed class is that it offers a specific type of dependence that can be useful when modeling data displaying spatial outliers, a property that has been somewhat ignored from modeling viewpoint in the literature for spatial point referenced data. Since the likelihood function involves analytically intractable integrals, we adopt the weighted pairwise likelihood as a method of estimation. The effectiveness of our methodology is illustrated with simulation experiments as well as with the analysis of a georeferenced dataset of mean temperatures in Middle East.
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Bevilacqua, M., Camano-Carrillo, C., & Porcu, E. (2022). Unifying compactly supported and Matern covariance functions in spatial statistics. J. Multivar. Anal., 189, 104949.
Abstract: The Matern family of covariance functions has played a central role in spatial statistics for decades, being a flexible parametric class with one parameter determining the smoothness of the paths of the underlying spatial field. This paper proposes a family of spatial covariance functions, which stems from a reparameterization of the generalized Wendland family. As for the Matern case, the proposed family allows for a continuous parameterization of the smoothness of the underlying Gaussian random field, being additionally compactly supported.
More importantly, we show that the proposed covariance family generalizes the Matern model which is attained as a special limit case. This implies that the (reparametrized) Generalized Wendland model is more flexible than the Matern model with an extra-parameter that allows for switching from compactly to globally supported covariance functions.
Our numerical experiments elucidate the speed of convergence of the proposed model to the Matern model. We also inspect the asymptotic distribution of the maximum likelihood method when estimating the parameters of the proposed covariance models under both increasing and fixed domain asymptotics. The effectiveness of our proposal is illustrated by analyzing a georeferenced dataset of mean temperatures over a region of French, and performing a re-analysis of a large spatial point referenced dataset of yearly total precipitation anomalies.
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Blasi, F., Caamano-Carrillo, C., Bevilacqua, M., & Furrer, R. (2022). A selective view of climatological data and likelihood estimation. Spat. Stat., 50(SI), 100596.
Abstract: This article gives a narrative overview of what constitutes climatological data and their typical features, with a focus on aspects relevant to statistical modeling. We restrict the discussion to univariate spatial fields and focus on maximum likelihood estimation. To address the problem of enormous datasets, we study three common approximation schemes: tapering, direct misspecification, and composite likelihood for Gaussian and nonGaussian distributions. We focus particularly on the so-called 'sinh-arcsinh distribution', obtained through a specific transformation of the Gaussian distribution. Because it has flexible marginal distributions – possibly skewed and/or heavy-tailed – it has a wide range of applications. One appealing property of the transformation involved is the existence of an explicit inverse transformation that makes likelihood-based methods straightforward. We describe a simulation study illustrating the effects of the different approximation schemes. To the best of our knowledge, a direct comparison of tapering, direct misspecification, and composite likelihood has never been made previously, and we show that direct misspecification is inferior. In some metrics, composite likelihood has a minor advantage over tapering. We use the estimation approaches to model a high-resolution global climate change field. All simulation code is available as a Docker container and is thus fully reproducible. Additionally, the present article describes where and how to get various climate datasets. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
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Canfora, F., Gomberoff, A., Oh, S. H., Rojas, F., & Salgado-Rebolledo, P. (2019). Meronic Einstein-Yang-Mills black hole in 5D and gravitational spin from isospin effect. J. High Energy Phys., (6), 32 pp.
Abstract: We construct an analytic black hole solution in SU(2) Einstein-Yang-Mills theory in five dimensions supporting a Meron field. The gauge field is proportional to a pure gauge and has a non-trivial topological charge. The would-be singularity at the Meron core gets shielded from the exterior by the black hole horizon. The metric has only one integration constant, namely, its ADM mass, which is shown to be finite once an appropriate boundary term is added to the action. The thermodynamics is also worked out, and a first-order phase transition, similar to the one occurring in the Reissner-Nordstrom case is identified. We also show that the solution produces a spin from isospin effect, i.e., even though the theory is constructed out of bosons only, the combined system of a scalar field and this background may become fermionic. More specifically, we study scalar excitations in this purely bosonic background and find that the system describes fermionic degrees of freedom at spatial infinity. Finally, for the asymptotically AdS(5) case, we study its consequences in the context of the AdS/CFT correspondence.
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Chandia, O. (2014). The non-minimal heterotic pure spinor string in a curved background. J. High Energy Phys., (3), 16 pp.
Abstract: We study the non-minimal pure spinor string in a curved background. We find that the minimal BRST invariance implies the existence of a non-trivial stress-energy tensor for the minimal and non-minimal variables in the heterotic curved background. We find constraint equations for the b ghost. We construct the b ghost as a solution of these constraints.
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Chandia, O., & Vallilo, B. C. (2015). Non-minimal fields of the pure spinor string in general curved backgrounds. J. High Energy Phys., (2), 16 pp.
Abstract: We study the coupling of the non-minimal ghost fields of the pure spinor superstring in general curved backgrounds. The coupling is found solving the consistency relations from the nilpotency of the non-minimal BRST charge.
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Chandia, O., Bevilaqua, L. I., & Vallilo, B. C. (2014). AdS pure spinor superstring in constant backgrounds. J. High Energy Phys., (6), 16 pp.
Abstract: In this paper we study the pure spinor formulation of the superstring in AdS(5) x S-5 around point particle solutions of the classical equations of motion. As a particular example we quantize the pure spinor string in the BMN background.
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Chandia, O., Linch, W. D., & Vallilo, B. C. (2017). Master symmetry in the AdS(5) x S-5 pure spinor string. J. High Energy Phys., (1), 15 pp.
Abstract: We lift the set of classical non-local symmetries recently studied by Klose, Loebbert, and Winkler in the context of Z(2) cosecs to the pure spinor description of the superstring in the AdS(5) x S-5 background.
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Chandia, O., Mikhailov, A., & Vallilo, B. C. (2013). A construction of integrated vertex operator in the pure spinor sigma-model in AdS(5) x S-5. J. High Energy Phys., 2013(11), 11 pp.
Abstract: Vertex operators in string theory me in two varieties: integrated and unintegrated. Understanding both types is important for the calculation of the string theory amplitudes. The relation between them is a descent procedure typically involving the b-ghost. In the pure spinor formalism vertex operators can be identified as cohomology classes of an infinite-dimensional Lie superalgebra formed by covariant derivatives. We show that in this language the construction of the integrated vertex from an unintegrated vertex is very straightforward, and amounts to the evaluation of the cocycle on the generalized Lax currents.
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Faouzi, T., Porcu, E., Kondrashuk, I., & Bevilacqua, M. (2023). Convergence arguments to bridge cauchy and matern covariance functions. Stat. Pap., Early Access.
Abstract: The Matern and the Generalized Cauchy families of covariance functions have a prominent role in spatial statistics as well as in a wealth of statistical applications. The Matern family is crucial to index mean-square differentiability of the associated Gaussian random field; the Cauchy family is a decoupler of the fractal dimension and Hurst effect for Gaussian random fields that are not self-similar. Our effort is devoted to prove that a scale-dependent family of covariance functions, obtained as a reparameterization of the Generalized Cauchy family, converges to a particular case of the Matern family, providing a somewhat surprising bridge between covariance models with light tails and covariance models that allow for long memory effect.
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Gonzalez, H., A., & Rojas, F. (2021). The structure of IR divergences in celestial gluon amplitudes. J. High Energy Phys., (6), 171.
Abstract: The all-loop resummation of SU(N) gauge theory amplitudes is known to factorize into an IR-divergent (soft and collinear) factor and a finite (hard) piece. The divergent factor is universal, whereas the hard function is a process-dependent quantity.We prove that this factorization persists for the corresponding celestial amplitudes. Moreover, the soft/collinear factor becomes a scalar correlator of the product of renormalized Wilson lines defined in terms of celestial data. Their effect on the hard amplitude is a shift in the scaling dimensions by an infinite amount, proportional to the cusp anomalous dimension. This leads us to conclude that the celestial-IR-safe gluon amplitude corresponds to a expectation value of operators dressed with Wilson line primaries. These results hold for finite N.In the large N limit, we show that the soft/collinear correlator can be described in terms of vertex operators in a Coulomb gas of colored scalar primaries with nearest neighbor interactions. In the particular cases of four and five gluons in planar N = 4 SYM theory, where the hard factor is known to exponentiate, we establish that the Mellin transform converges in the UV thanks to the fact that the cusp anomalous dimension is a positive quantity. In other words, the very existence of the full celestial amplitude is owed to the positivity of the cusp anomalous dimension.
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Gonzalez, H. A., Puhm, A.,, & Rojas, F. (2020). Loop corrections to celestial amplitudes. Phys. Rev. D., 102, 126027.
Abstract: We study the effect of loop corrections to conformal correlators on the celestial sphere at null infinity. We first analyze finite one-loop celestial amplitudes in pure Yang-Mills theory and Einstein gravity. We then turn to our main focus: infrared divergent loop amplitudes in planar N=4
super–Yang-Mills theory. We compute the celestial one-loop amplitude in dimensional regularization and show that it can be recast as an operator acting on the celestial tree-level amplitude. This extends to any loop order, and the resummation of all planar loops enables us to write down an expression for the all-loop celestial amplitude. Finally, we show that the exponentiated all-loop expression given by the Bern-Dixon-Smirnov (BDS) formula gets promoted on the celestial sphere to an operator acting on the tree-level conformal correlation function, thus yielding, the celestial BDS formula.
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Ibarra, C., O'Ryan, R., & Silva, B. (2018). Applying knowledge governance to understand the role of science in environmental regulation: The case of arsenic in Chile. Environ. Sci. Policy, 86, 115–124.
Abstract: The relationship between scientific knowledge and decision-making surrounding environmental issues is complex and represents a flourishing area of scholarship and practice. However, a sense of frustration persists regarding efforts to increase the use of science for decision-making. Regulations of copper smelter arsenic emissions developed in Chile during the 1990s represent a successful example of science informing policy making. The case involved production and use of local science in contrast to the common practice of copying international ambient standards. In this paper, we investigate arsenic regulation in Chile in the 1990s and focus on the role of the major science intervention during the process, project FONDEF 2-24. The case is examined through the lens of knowledge governance (van Kerkhoff and Pilbeam, 2017). This theoretically-oriented approach guides our critical reflection on the relationship between knowledge and policy making, taking into consideration the formal and informal rules that shape the intervention and the underlying social and cultural patterns. The success of the science intervention's influence on policy is better understood with such a perspective. We expand the knowledge governance approach by scrutinizing the relations of coherence between levels of analysis to assess their alignment. The approach could be helpful for studying other cases, particularly at times when a new field of policy is emerging.
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Mahajan, S. M., & Asenjo, F. A. (2022). Interacting quantum and classical waves: Resonant and non-resonant energy transfer to electrons immersed in an intense electromagnetic wave. Phys. Plasmas, 29(2), 022107.
Abstract: Dynamics of electrons subjected to a constant amplitude classical electromagnetic (EM) wave is investigated as a fundamental, representative problem in the physics of interacting quantum and classical waves. In the nonrelativistic regime (electrons as Schrodinger waves), the electron energy acquires a constant and a time dependent part. Driven by EM waves, both parts scale strongly with the amplitude, but we expect no resonant enhancement since the parallel electron “speed ” of nonrelativistic electrons could never match the wave phase velocity. In the relativistic regime (electron as a Klein-Gordon wave), however, a class of electron waves (with parallel speed matching the EM phase speed) are resonantly excited to extremely high energies. Such a direct resonant energy transfer from intense electromagnetic waves constitutes a mechanism that could, in principle, power the most energetic of cosmic rays (this mechanism will work on protons just as well). Some predictions of the theory will, hopefully, be tested in laboratory laser experiments. The nonrelativistic calculations will also be examined in the context of recent experiments using photon-induced near-field electron microscopy in detail.
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Mahajan, S. M., Asenjo, F. A., & Hazeltine, R. D. (2015). Comparison of the electron-spin force and radiation reaction force. Mon. Not. Roy. Astron. Soc., 446(4), 4112–4115.
Abstract: It is shown that the forces that originate from the electron-spin interacting with the electromagnetic field can play, along with the Lorentz force, a fundamentally important role in determining the electron motion in a high energy density plasma embedded in strong high-frequency radiation, a situation that pertains to both laser-produced and astrophysical systems. These forces, for instance, dominate the standard radiation reaction force as long as there is a 'sufficiently' strong ambient magnetic field for affecting spin alignment. The inclusion of spin forces in any advanced modelling of electron dynamics pertaining to high energy density systems (for instance in particle-in-cell codes), therefore, is a must.
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Morales-Navarrete, D., Bevilacqua, M., Caamano-Carrillo, C., & Castro, L. M. (2023). Modeling Point Referenced Spatial Count Data: A Poisson Process Approach. J. Am. Stat. Assoc., Early Access.
Abstract: Random fields are useful mathematical tools for representing natural phenomena with complex dependence structures in space and/or time. In particular, the Gaussian random field is commonly used due to its attractive properties and mathematical tractability. However, this assumption seems to be restrictive when dealing with counting data. To deal with this situation, we propose a random field with a Poisson marginal distribution considering a sequence of independent copies of a random field with an exponential marginal distribution as “inter-arrival times ” in the counting renewal processes framework. Our proposal can be viewed as a spatial generalization of the Poisson counting process. Unlike the classical hierarchical Poisson Log-Gaussian model, our proposal generates a (non)-stationary random field that is mean square continuous and with Poisson marginal distributions. For the proposed Poisson spatial random field, analytic expressions for the covariance function and the bivariate distribution are provided. In an extensive simulation study, we investigate the weighted pairwise likelihood as a method for estimating the Poisson random field parameters. Finally, the effectiveness of our methodology is illustrated by an analysis of reindeer pellet-group survey data, where a zero-inflated version of the proposed model is compared with zero-inflated Poisson Log-Gaussian and Poisson Gaussian copula models. for this article, including technical proofs and R code for reproducing the work, are available as an online supplement.
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Morales-Onate, V., Crudu, F., & Bevilacqua, M. (2021). Blockwise Euclidean likelihood for spatio-temporal covariance models. Econ. Stat., 20, 176–201.
Abstract: A spatio-temporal blockwise Euclidean likelihood method for the estimation of covariance models when dealing with large spatio-temporal Gaussian data is proposed. The method uses moment conditions coming from the score of the pairwise composite likelihood. The blockwise approach guarantees considerable computational improvements over the standard pairwise composite likelihood method. In order to further speed up computation, a general purpose graphics processing unit implementation using OpenCL is implemented. The asymptotic properties of the proposed estimator are derived and the finite sample properties of this methodology by means of a simulation study highlighting the computational gains of the OpenCL graphics processing unit implementation. Finally, there is an application of the estimation method to a wind component data set. (C) 2021 EcoSta Econometrics and Statistics. Published by Elsevier B.V. All rights reserved.
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Nastase, H., Rojas, F., & Rubio, C. (2022). Celestial IR divergences in general most-subleading-color gluon and gravity amplitudes. J. High Energy Phys., (1), 136.
Abstract: Gluon amplitudes at most-subleading order in the 1/N expansion share a remarkable simplicity with graviton amplitudes: collinear divergences are completely absent in both and, as a consequence, their full IR behavior arises from soft gluon/graviton exchange among the external states. In this paper we study the effect of all-loop IR divergences of celestial most-subleading color gluon amplitudes and their similarities with the celestial gravity case. In particular, a simple celestial exponentiation formula for the dipole part can be written. We also analize how this exponentiation is modified by non-dipole contributions. Finally we also show that, in the Regge limit, the soft factor satisfies the Knizhnik-Zamolodchikov equation hinting at the possibility that, in this limit, an effective Wess-Zumino-Witten model would describe the dynamics of the infrared sector.
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