arXiv subjects

Daniele Musso

Publications and source records attributed to Daniele Musso.

44 records · Page 3Linked to original sources

arXiv2014

Coexistence of two vector order parameters: a holographic model for ferromagnetic superconductivity

We study a generalization of the standard holographic p-wave superconductor featuring two interacting vector order parameters. Basing our argument on the symmetry and linear response properties of the model, we propose it as a holographic effective theory describing a strongly coupled ferromagnetic superconductor. We show that the two order parameters undergo concomitant condensations as a manifestation of an intrinsically interlaced electric/magnetic dynamics. Such intertwined dynamics is confirmed by the study of the transport properties. We characterize thoroughly the equilibrium and the linear response (i.e. optical conductivity and magnetic susceptibility) of the model at hand by means of a probe approximation analysis. Some insight about the effects of backreaction in the normal phase can be gained by analogy with the s-wave unbalanced holographic superconductor.

hep-th↗

arXiv2013

Minimal Model for an Unbalanced Holographic Superconductor

We describe the simplest holographic model for an s-wave unbalanced superconductor in 2+1 dimensions. We study its phase diagram and linear response features with particular attention to the possibility of spatially modulated phases (LOFF) and mixed spin-electric properties. The normal phase of the model at hand allows us to analyze a strong-coupling generalization of Mott two-current model for spintronic systems; the superconducting phase features an interesting DC spin-superconductivity without spin-symmetry breaking .

hep-th↗

arXiv2013

Competition/Enhancement of Two Probe Order Parameters in the Unbalanced Holographic Superconductor

We introduce and study a simple unbalanced holographic superconductor model with two scalar order parameters. The attention is focused on the possibility of coexisting orderings corresponding to the concomitant condensation of two scalar operators. Through a probe analysis we show that an attractive or repulsive direct interaction between the two bulk scalars leads respectively to competition and enhancement of the associated condensates. The system at hand is a toy model for studying generic multiple ordering in a strongly coupled context and some comments are given about its applicability to the ferromagnetic unconventional superconductors.

hep-th↗

arXiv2012

Field Theory Interpretation of N=2 Stringy Instantons

We consider stringy instanton contributions to the prepotential of low-energy N=2 theories engineered by D-brane set ups at orbifold and orientifold singularities. We show that such contributions can always be reproduced in a purely field theoretic UV completion. We perform the explicit check up to instanton number three, both for Sp(0) and U(1) stringy instantons, the latter being introduced for the purpose. We further argue that the UV completion that we propose, though weakly coupled, can be smoothly mapped to a gravity-dual inspired UV completion consisting of a cascade of baryonic root transitions.

hep-th↗

arXiv2012

D-branes and Non-Perturbative Quantum Field Theory: Stringy Instantons and Strongly Coupled Spintronics

The non-perturbative dynamics of quantum field theories is studied using theoretical tools inspired by string formalism. Two main lines are developed: the analysis of stringy instantons in a class of four-dimensional N=2 gauge theories and the holographic study of the minimal model for a strongly coupled unbalanced superconductor. The field theory instanton calculus admits a natural and efficient description in terms of D-brane models. In addition, the string viewpoint offers the possibility of generalizing the ordinary instanton configurations. Even though such generalized, or stringy, instantons would be absent in a purely field-theoretical, low-energy treatment, we demonstrate that they do alter the IR effective description of the brane dynamics by introducing contributions related to the string scale. In the first part of this thesis we compute explicitly the stringy instanton corrections to the effective prepotential in a class of quiver gauge theories. In the second part of the thesis, we present a detailed analysis of the minimal holographic setup yielding an effective description of a superconductor with two Abelian currents. The model contains a scalar field whose condensation produces a spontaneous symmetry breaking which describes the transition to a superfluid phase. This system has important applications in both QCD and condensed matter physics; moreover, it allows us to study mixed electric-spin transport properties (i.e. spintronics) at strong coupling.

hep-th↗

arXiv2012

Unbalanced Holographic Superconductors and Spintronics

We present a minimal holographic model for s-wave superconductivity with unbalanced Fermi mixtures, in 2+1 dimensions at strong coupling. The breaking of a U(1)_A "charge" symmetry is driven by a non-trivial profile for a charged scalar field in a charged asymptotically AdS_4 black hole. The chemical potential imbalance is implemented by turning on the temporal component of a U(1)_B "spin" field under which the scalar field is uncharged. We study the phase diagram of the model and comment on the eventual (non) occurrence of LOFF-like inhomogeneous superconducting phases. Moreover, we study "charge" and "spin" transport, implementing a holographic realization (and a generalization thereof to superconducting setups) of Mott's two-current model which provides the theoretical basis of modern spintronics. Finally we comment on possible string or M-theory embeddings of our model and its higher dimensional generalizations, within consistent Kaluza-Klein truncations and brane-anti brane setups.

hep-th↗

arXiv2011

Stringy Instantons in SU(N) N=2 Non-Conformal Gauge Theories

In this paper we explicitly obtain the leading corrections to the SU(N) N=2 prepotential due to stringy instantons both in flat space-time and in the presence of a non-trivial graviphoton background field. We show that the stringy corrections to the prepotential are expressible in terms of the elementary symmetric polynomials. For N>2 the theory is not conformal; we discuss the introduction of an explicit dependence on the string scale α' in the low-energy effective action through the stringy non-perturbative sector.

hep-th↗

arXiv2010

Stringy instanton effects in N=2 gauge theories

We study the non-perturbative effects induced by stringy instantons on N=2 SU}(N) gauge theories in four dimensions, realized on fractional D3 branes in a C^3/Z_3 orientifold. The stringy instantons, corresponding to D(-1) branes that occupy a node of the orientifold quiver diagram where no D3 brane is present, have the right content of zero-modes to produce non-perturbative terms in the four-dimensional effective action. In the SU(2) theory these terms have the same structure for all instanton numbers and yield a series of non-perturbative corrections to the prepotential. We explicitly compute these corrections up to instanton number k=5 using localization methods.

hep-th↗