Pomeranchuk instabilities in holographic metals

We develop a method to detect instabilities leading to nematic phases in strongly coupled metallic systems. We do so by adapting the well-known Pomeranchuk technique to a weakly coupled system of fermions in a curved asymptotically AdS bulk. The resulting unstable modes are interpreted as corresponding to instabilities on the dual strongly coupled holographic metal. We apply our technique to a relativistic $3+1$-dimensional bulk with generic quartic fermionic couplings, and explore the phase diagram at zero temperature for finite values of the fermion mass and chemical potential, varying the couplings. We find a wide region of parameters where the system is stable, which is simply connected and localized around the origin of coupling space.Comment: Replaced by final version, published in JHE

Holographic phase transitions from higgsed, non abelian charged black holes

We find solutions of a gravity-Yang-Mills-Higgs theory in four dimensions that represent asymptotic anti-de Sitter charged black holes with partial/full gauge symme-try breaking. We then apply the AdS/CFT correspondence to study the strong coupling regime of a 2 + 1 quantum field theory at temperature T and finite chemical potential, which undergoes transitions to phases exhibiting the condensation of a composite charged vector operator below a critical temperature Tc, presumably describing p + ip/p-wave su-perconductors. In the case of p + ip-wave superconductors the transitions are always of second order. But for p-wave superconductors we determine the existence of a critical value αTc of the gravitational coupling (for fixed Higgs v.e.v. parameter mW) beyond which the transitions become of first order. As a by-product, we show that the p-wave phase is energetically favored over the p + ip one, for any values of the parameters. We also find the ground state solutions corresponding to zero temperature. Such states are described by domain wall geometries that interpolate between AdST4 spaces with different light velocities, and for a given mW, they exist below a critical value of the coupling. The behavior of the order parameter as function of the gravitational coupling near the critical coupling suggests the presence of second order quantum phase transitions. We finally study the dependence of the solution on the Higgs coupling, and find the existence of a critical value beyond which no condensed solution is present.Facultad de Ciencias ExactasInstituto de Física La Plat

Aplicaciones de la correspondencia AdS/CFT en el ámbito de la física de la materia condensada

En esta tesis se consideraron varios tópicos asociados a la aplicación de la correspondencia AdS/CFT a sistemas de materia condensada. En particular se estudiaron modelos holográficos de superconductores, metales extraños e inestabilidades fermiónicas que pueden presentar los mismos. El capı́tulo 1 es una introducción donde se exponen los objetivos y motivaciones para estudiar estos sistemas. En el capı́tulo 2 se resumen las ideas y conceptos fundamentales para entender la teorı́a de cuerdas y la correspondencia AdS/CFT . En el capı́tulo 3 se introducen conceptos básicos de la teorı́a de la Materia Condensada pertinentes a la Tesis. En primer lugar los superconductores, cuáles son los fenómenos fı́sicos detrás de ellos y cómo es el marco teórico-matemático para describirlos. Posteriormente se introducen los lı́quidos de Fermi, su descripción a través de la teorı́a de Landau, y la existencia de una fase denominada de metal extraño que experimentan los superconductores de alta temperatura, donde dicha teorı́a no es aplicable. En el capítulo 4 se introducen los modelos holográficos más básicos para describir superconductores, metales extraños y sistemas de electrones a potencial químico finito. En el capı́tulo 5 se presenta el análisis de un sistema del tipo gravedad-Yang-Mills-Higgs que modela holográficamente un superconductor de onda p/p + ip. En tal sistema se calculan varias propiedades fı́sicas de interés y se hace una comparación entre ellas. Se estudian además soluciones a temperatura y entropı́a nulas. En el capı́tulo 6 se analizan funciones espectrales de campos fermiónicos a temperatura finita en el fondo de un superconductor de onda p, teniendo en cuenta el efecto sobre la geometrı́a de los campos de calibre. En el capı́tulo 7 se estudia el cruce entre un lı́quido de Fermi y un metal extraño introduciendo una variable de dopaje desde el lado gravitatorio. Por último, en el capítulo 8 se generaliza el método de Pomeranchuk en un espacio-tiempo curvo específico, para poder estudiar inestabilidades de la superficie de Fermi de un sistema de electrones fuertemente acoplado que pueden dar lugar a fases nemáticas o esmécticas.Facultad de Ciencias Exacta

Desiccating stress-induced disruption of ocular surface immune tolerance drives dry eye disease

Dry eye is an allegedly autoimmune disorder for which the initiatingmechanisms and the targeted antigens in the ocular surface are not known,yet there is extensive evidence that a localized T helper type 1 (Th1)/Th17effector T cell response is responsible for its pathogenesis. In this work, weexplore the reconciling hypothesis that desiccating stress, which is usuallyconsidered an exacerbating factor, could actually be sufficient to skew theocular surface?s mucosal response to any antigen and therefore drive thedisease. Using a mouse model of dry eye, we found that desiccating stresscauses a nuclear factor kappa B (NF-jB)- and time-dependent disruption ofthe ocular surface?s immune tolerance to exogenous ovalbumin. Thispathogenic event is mediated by increased Th1 and Th17 T cells andreduced regulatory T cells in the draining lymph nodes. Conversely, topicalNF-jB inhibitors reduced corneal epithelial damage and interleukin (IL)-1band IL-6 levels in the ocular surface of mice under desiccating stress. Theobserved effect was mediated by an augmented regulatory T cell response, afinding that highlights the role of mucosal tolerance disruption in dry eyepathogenesis. Remarkably, the NF-jB pathway is also involved in mucosaltolerance disruption in other ocular surface disorders. Together, theseresults suggest that targeting of mucosal NF-jB activation could havetherapeutic potential in dry eye.Fil: Guzman, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Keitelman, Irene Angélica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Sabbione, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Trevani, Analía Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Giordano, Mirta Nilda. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Galletti, Jeremías Gastón. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Fermionic spectral functions in backreacting p-wave superconductors at finite temperature

We investigate the spectral function of fermions in a p-wave superconducting state, at finite both temperature and gravitational coupling, using the AdS/CFT correspondence and extending previous research. We found that, for any coupling below a critical value, the system behaves as its zero temperature limit. By increasing the coupling, the “peak-dip-hump” structure that characterizes the spectral function at fixed momenta disappears. In the region where the normal/superconductor phase transition is first order, the presence of a non-zero order parameter is reflected in the absence of rotational symmetry in the fermionic spectral function at the critical temperature.Facultad de Ciencias ExactasInstituto de Física La Plat

Restoring Conjunctival Tolerance by Topical Nuclear Factor–κB Inhibitors Reduces Preservative-Facilitated Allergic Conjunctivitis in Mice

Purpose.: To evaluate the role of nuclear factor–κB (NF-κB) activation in eye drop preservative toxicity and the effect of topical NF-κB inhibitors on preservative-facilitated allergic conjunctivitis. Methods.: Balb/c mice were instilled ovalbumin (OVA) combined with benzalkonium chloride (BAK) and/or NF-κB inhibitors in both eyes. After immunization, T-cell responses and antigen-induced ocular inflammation were evaluated. Nuclear factor–κB activation and associated inflammatory changes also were assessed in murine eyes and in an epithelial cell line after BAK exposure. Results.: Benzalkonium chloride promoted allergic inflammation and leukocyte infiltration of the conjunctiva. Topical NF-κB inhibitors blocked the disruptive effect of BAK on conjunctival immunological tolerance and ameliorated subsequent ocular allergic reactions. In line with these findings, BAK induced NF-κB activation and the secretion of IL-6 and granulocyte-monocyte colony-stimulating factor in an epithelial cell line and in the conjunctiva of instilled mice. In addition, BAK favored major histocompatibility complex (MHC) II expression in cultured epithelial cells in an NF-κB–dependent fashion after interaction with T cells. Conclusions.: Benzalkonium chloride triggers conjunctival epithelial NF-κB activation, which seems to mediate some of its immune side effects, such as proinflammatory cytokine release and increased MHC II expression. Breakdown of conjunctival tolerance by BAK favors allergic inflammation, and this effect can be prevented in mice by topical NF-κB inhibitors. These results suggest a new pharmacological target for preservative toxicity and highlight the importance of conjunctival tolerance in ocular surface homeostasis.Fil: Guzman, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Sabbione, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Gabelloni, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Vanzulli, Silvia. Academia Nacional de Medicina de Buenos Aires; ArgentinaFil: Trevani, Analía Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Giordano, Mirta Nilda. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Galletti, Jeremías Gastón. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Neutralidad valorativa y objetividad en la visión de la ciencia de Max Weber y Niklas Luhmann

Cuando Max Weber postula la idea de una neutralidad valorativa que debe seguir todo investigador en ciencias sociales para dotar a su trabajo de rasgos de cientificidad, discute uno de los sentidos que ha adquirido la noción de “objetividad”. De acuerdo con el autor, si los pasos metodológicos se despliegan de manera adecuada, es posible dejar a los valores por fuera de los resultados de toda labor sociológica. Desde una óptica diferente, Niklas Luhmann elabora una teoría de la sociedad sobre la base de sistemas de comunicación autorreferentes y autopoiéticos; en su descripción de la ciencia, reconoce un lugar cognitivo para los valores pero parece sostener una posición en la que la mirada sociológica puede hacer de ellos un objeto, sin quedar atrapada en sus condicionamientos. En este marco, el objetivo de nuestro trabajo consiste en analizar comparativamente los supuestos que subyacen a la tesis weberiana de la neutralidad valorativa y la objetividad cognoscitiva con el postulado de Luhmann que informa acerca del cierre autopoiético del sistema científico.Mesa 5: El Jardín de senderos que se bifurcan. Teoría Social, Teoría sociológica, Sociología: la pregunta por lo social y sus múltiples respuestasFacultad de Humanidades y Ciencias de la Educació

Strange metal crossover in the doped holographic superconductor

In a recent paper, Kiritsis and Li presented a holographic model to study the competition between different orders at finite doping in holographic superconductors. In the present work, we introduce fermions into such model and study the fermionic spectral functions in the normal phase at zero and finite temperatures. Combining analytic and numerical methods, we found that there is a crossover from a strange metal with short lived excitations at small doping, into a Fermi liquid with well defined quasiparticles at large doping. The critical doping at which excitations becomes long lived increases with temperature. The emerging phase diagram is qualitatively similar to that of High Temperature Superconductors.Instituto de Física La Plat

Thermodynamics of the classical spin-ice model with nearest neighbour interactions using the Wang-Landau algorithm

In this article we study the classical nearest-neighbour spin-ice model (nnSI) by means of Monte Carlo simulations, using the Wang-Landau algorithm. The nnSI describes several of the salient features of the spin-ice materials. Despite its simplicity it exhibits a remarkably rich behaviour. The model has been studied using a variety of techniques, thus it serves as an ideal benchmark to test the capabilities of the Wang Landau algorithm in magnetically frustrated systems. We study in detail the residual entropy of the nnSI and, by introducing an applied magnetic field in two different crystallographic directions ([111] and [100]), we explore the physics of the kagome-ice phase, the transition to full polarisation, and the three dimensional Kasteleyn transition. In the latter case, we discuss how additional constraints can be added to the Hamiltonian, by taking into account a selective choice of states in the partition function and, then, show how this choice leads to the realization of the ideal Kasteleyn transition in the system.Instituto de Física de Líquidos y Sistemas BiológicosFacultad de Ciencias Exacta

Pomeranchuk instabilities in holographic metals

We develop a method to detect instabilities leading to nematic phases in strongly coupled metallic systems. We do so by adapting the well-known Pomeranchuk technique to a weakly coupled system of fermions in a curved asymptotically AdS bulk. The resulting unstable modes are interpreted as corresponding to instabilities on the dual strongly coupled holographic metal. We apply our technique to a relativistic 3 + 1- dimensional bulk with generic quartic fermionic couplings, and explore the phase diagram at zero temperature for finite values of the fermion mass and chemical potential, varying the couplings. We find a wide region of parameters where the system is stable, which is simply connected and localized around the origin of coupling space.Instituto de Física La Plat