Formalismo línea de mundo para un campo escalar en variedades curvas y con borde

El formalismo línea de mundo es un esquema útil en teoría cuántica de campos que también se ha convertido en una poderosa herramienta para realizar cálculos numéricos. El ingrediente principal de este formalismo consiste en la (primera) cuantización de una partícula puntual auxiliar cuyas amplitudes de transición se corresponden con el núcleo de calor (heat-kernel) del operador de fluctuaciones cuánticas de la teoría de campos. No obstante, para estudiar un campo cuántico en una variedad con borde es necesario restringir el dominio de integración de los caminos de la partícula auxiliar, tomando un subconjunto específico de líneas de mundo contenidas en dicha variedad. El principal objetivo del presente trabajo consiste en mostrar cómo implementar esta restricción para el caso de un campo escalar en ciertas geometrías con borde, poniendo a prueba los resultados al considerar que el campo se encuentra confinado en una esfera D-dimensional bajo condiciones de borde de Dirichlet, Neumann y Robin. Se computan explícitamente los primeros coeficientes del heat-kernel para el caso D=2 como verificación de la construcción empleada. Además de la tarea mencionada, se discuten aspectos varios de las teorías cuánticas de campos y sus aplicaciones, con énfasis en el formalismo línea de mundo. Es en base a estos aspectos que se construye el formalismo, primero en espacios sin borde y luego en variedades con borde. Al final se mencionan posibles generalizaciones de la construcción presentada.Facultad de Ciencias Exacta

Local Neumann semitransparent layers: Resummation, pair production, and duality

We consider local semitransparent Neumann boundary conditions for a quantum scalar field as imposed by a quadratic coupling to a source localized on a flat codimension-one surface. Upon a proper regularization to give meaning to the interaction, we interpret the effective action as a theory in a first-quantized phase space. We compute the relevant heat kernel to all order in a homogeneous background and quadratic order in perturbations, giving a closed expression for the corresponding effective action in D=4. In the dynamical case, we analyze the pair production caused by a harmonic perturbation and a Sauter pulse. Notably, we prove the existence of a strong/weak duality that links this Neumann field theory to the analog Dirichlet one.Fil: Ahmadiniaz, N.. Helmholtz-Zentrum Dresden-Rossendorf; AlemaniaFil: Franchino Viñas, Sebastián Alberto. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Manzo, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Worldline formalism for a confined scalar field

The worldline formalism is a useful scheme in quantum field theory which has also become a powerful tool for numerical computations. The key ingredient in this formalism is the first quantization of an auxiliary point-particle whose transition amplitudes correspond to the heat-kernel of the operator of quantum fluctuations of the field theory. However, to study a quantum field which is confined within some boundaries one needs to restrict the path integration domain of the auxiliary point-particle to a specific subset of worldlines enclosed by those boundaries. We show how to implement this restriction for the case of a scalar field confined to the D-dimensional ball under Dirichlet and Neumann boundary conditions, and compute the first few heat-kernel coefficients as a verification of our construction. We argue that this approach could admit different generalizations.Fil: Corradini, Olindo. Università Di Modena E Reggio Emilia.; Italia. Istituto Nazionale Di Fisica Nucleare; ItaliaFil: Edwards, James P.. Universidad Michoacana de San Nicolás de Hidalgo; MéxicoFil: Huet, Idrish. Universidad Nacional Autónoma de México; MéxicoFil: Manzo, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: González Pisani, Pablo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Local Neumann semitransparent layers: resummation, pair production and duality

We consider local semitransparent Neumann boundary conditions for a quantum scalar field as imposed by a quadratic coupling to a source localized on a flat codimension-one surface. Upon a proper regularization to give meaning to the interaction, we interpret the effective action as a theory in a first-quantized phase space. We compute the relevant heat-kernel to all order in a homogeneous background and to quadratic order in perturbations, giving a closed expression for the corresponding effective action in D=4. In the dynamical case, we analyze the pair production caused by a harmonic perturbation and by a Sauter pulse. Notably, we prove the existence of a strong/weak duality that links this Neumann field theory to the analogue Dirichlet one.Helmholtz-Zentrum Dresden-RossendorfDepartamento de FísicaInstituto de Física La PlataCentro Atómico BarilocheInstituto BalseiroConsejo Nacional de Investigaciones Científicas y Técnica

Worldline formalism for a confined scalar field

The worldline formalism is a useful scheme in quantum field theory which has also become a powerful tool for numerical computations. The key ingredient in this formalism is the first quantization of an auxiliary point-particle whose transition amplitudes correspond to the heat-kernel of the operator of quantum fluctuations of the field theory. However, to study a quantum field which is confined within some boundaries one needs to restrict the path integration domain of the auxiliary point-particle to a specific subset of worldlines enclosed by those boundaries. We show how to implement this restriction for the case of a scalar field confined to the D-dimensional ball under Dirichlet and Neumann boundary conditions, and compute the first few heat-kernel coefficients as a verification of our construction. We argue that this approach could admit different generalizations.Facultad de Ciencias ExactasInstituto de Física La Plat

Worldline approach for spinor fields in manifolds with boundaries

Abstract The worldline formalism is a useful scheme in Quantum Field Theory which has also become a powerful tool for numerical computations. It is based on the first quantisation of a point-particle whose transition amplitudes correspond to the heat-kernel of the operator of quantum fluctuations of the field theory. However, to study a quantum field theory in a bounded manifold one needs to restrict the path integration domain of the point-particle to a specific subset of worldlines enclosed by those boundaries. In the present article it is shown how to implement this restriction for the case of a spinor field in a two-dimensional curved half-plane under MIT bag boundary conditions, and compute the first few heat-kernel coefficients as a verification of the proposed construction. This construction admits several generalisations

Complex effects of reward upshift on consummatory behavior

Exposing rats to an upshift from a small reward to a larger reward sometimes yields evidence of consummatory successive positive contrast (cSPC), an effect that could be a suitable animal model of positive emotion. However, cSPC is an unreliable effect. Ten experiments explored the effects of an upshift in sucrose or saccharin concentration on consummatory behavior under several conditions. There was occasional evidence of cSPC, but mostly a combination of increased consummatory behavior relative to preshift reward concentrations and a reducedbehavioral level relative to unshifted controls. Such a pattern is consistent with processes causing opposite changes on behavior. Reward upshift may induce processes that suppress behavior, such as taste neophobia (induced by an intense sucrose taste) and generalization decrement (induced by novelty in reward conditions after the upshift). An experiment tested the role of such novelty-related effects by preexposing animals to either the upshift concentration(12% sucrose) or water during three days before the start of the experiment. Sucrosepreexposed animals drank significantly more than water-preexposed animals during the upshift, but just as much as unshifted controls (i.e., no evidence of cSPC). These results suggest that cSPC may be difficult to obtain reliably because reward upshift induces opposing processes.However, they also seriously question the ontological status of cSPC.Fil: Annicchiarico, Ivan. Texas Christian University; Estados UnidosFil: Glueck, Amanda C.. Texas Christian University; Estados UnidosFil: Cuenya, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; ArgentinaFil: Kawasaki, Katsuyoshi. Hoshi University; JapónFil: Conrad, Shannon E.. Texas Christian University; Estados UnidosFil: Papini, Mauricio Roberto. Texas Christian University; Estados Unido

The Pre-Aksumite Period: indigenous origins and development in the Horn of Africa

The Pre-Aksumite Period (mid-second to late first millennia BC) witnessed the rise of complex societies in the Horn of Africa. Archaeological survey and excavations in the Gulo Makeda region of Eastern Tigrai by the Eastern Tigrai Archaeological Project (ETAP) have produced new data and insights into this critical juncture in the cultural history of the region. Based on data from Mezber and other archaeological sites, we present a new Pre-Aksumite chronology and discuss the material culture, settlement, political organisation, economy, agricultural history and regional interactions of this period. We recommend the use of the term ‘Pre-Aksumite Period’ to encompass this time when the earliest polities developed in the region. Mezber provides us with a glimpse into the lifeways of indigenous peoples inhabiting the northern Horn of Africa who encountered South Arabian visitors to the region during the early first millennium BC. Data from Mezber shift our focus from external influences to considering the culture and development of autochthonous peoples of the Ethiopian/Eritrean highlands who had an active role in negotiating cultural contacts. This perspective constitutes a missing piece of the puzzle needed to better understand the broader socio-economic, political and cultural dynamics of the Pre-Aksumite Period.ETAP investigations at Mezber were financially supported by three grants from the Social Sciences and Humanities Research Council of Canada (SSHRC), including Standard Research Grants 410-2007-2472, 410-2011-1646 and Insight Grant 435-2014-01. Further support was obtained by grants from Simon Fraser University, including four SSHRC/SFU Institutional Grants and a VP Research SSHRC 4A grant. Field and laboratory microbotanical work completed by AR-G and CL was developed within the framework of the RAINDROPS project, funded by the European Research Council (ERC-Stg 759800) and both are part of CaSEs, a recognised research group of the Generalitat De Catalunya (AGAUR SGR-e-2017-212)

Separating actin-dependent chemokine receptor nanoclustering from dimerization indicates a role for clustering in CXCR4 signaling and function.

A current challenge in cell motility studies is to understand the molecular and physical mechanisms that govern chemokine receptor nanoscale organization at the cell membrane, and their influence on cell response. Using single-particle tracking and super-resolution microscopy, we found that the chemokine receptor CXCR4 forms basal nanoclusters in resting T cells, whose extent, dynamics, and signaling strength are modulated by the orchestrated action of the actin cytoskeleton, the co-receptor CD4, and its ligand CXCL12. We identified three CXCR4 structural residues that are crucial for nanoclustering and generated an oligomerization-defective mutant that dimerized but did not form nanoclusters in response to CXCL12, which severely impaired signaling. Overall, our data provide new insights to the field of chemokine biology by showing that receptor dimerization in the absence of nanoclustering is unable to fully support CXCL12-mediated responses, including signaling and cell function in vivoThis work was supported by grants from the Spanish Ministry of Economy and Competitiveness (SAF 2014-53416-R, SAF 2017-82940-R AEI/FEDER, EU) and the RETICS Program (RD16/0012/0006; RIER), Ministry of Economy and Competitiveness, Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2013-0347; SEV-2015-0522), and Fundación Privada Cellex and Generalitat de Catalunya (CERCA program). L.M.-M. is supported by the COMFUTURO program of the Spanish Research Council General Foundation.Peer reviewe