arXiv subjects

Alberto Mariotti

Publications and source records attributed to Alberto Mariotti.

At least 55 records · Page 3Linked to original sources

arXiv2014

Anatomy of the Amplituhedron

We initiate a comprehensive investigation of the geometry of the amplituhedron, a recently found geometric object whose volume calculates the integrand of scattering amplitudes in planar N=4 SYM theory. We do so by introducing and studying its stratification, focusing on four-point amplitudes. The new stratification exhibits interesting combinatorial properties and positivity is neatly captured by permutations. As explicit examples, we find all boundaries for the two and three loop amplitudes and related geometries. We recover the stratifications of some of these geometries from the singularities of the corresponding integrands, providing a non-trivial test of the amplituhedron/scattering amplitude correspondence. We finally introduce a deformation of the stratification with remarkably simple topological properties.

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arXiv2014

Novel Higgs Potentials from Gauge Mediation of Exact Scale Breaking

We present a gauge mediation principle for BSM theories where exact UV scale invariance is broken in a hidden sector. The relevant configurations are those in which the Standard Model and a hidden sector emanate from a scale invariant pair of UV theories that communicate only via gauge interactions. We compute the radiatively induced Higgs potential which contains logarithmic mass-squared terms that lead to unusual Higgs self-couplings. Its other couplings are unchanged.

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arXiv2014

Multiphoton signatures of goldstini at the LHC

We study models of gauge mediated SUSY breaking with more than one hidden sector. In these models the neutralino sector of the MSSM is supplemented with additional light neutral fermions, the nearly massless gravitino and the massive pseudo-goldstini. For the case where the Bino is the lightest ordinary SUSY particle, its preferred decay is to a photon and the heaviest pseudo-goldstino, which generically cascades down to lighter pseudo-goldstini, or to the gravitino, in association with photons. This gives rise to multiphoton plus missing energy signatures at the LHC. We investigate in detail simplified models where the SUSY spectrum consists of the right-handed sleptons, a Bino-like neutralino, the pseudo-goldstini and the gravitino. We compare against existing LHC searches and show that the sensitivity to our models could be significantly improved by relaxing the kinematic cuts and requiring additional final state particles. We propose inclusive searches in the final state with at least three photons plus missing energy and in the final state with at least two photons plus two leptons plus missing energy, the former being sensitive to any production mode and the latter being optimized for slepton pair production. We show that they could lead to an observation (or strong constraints) already with the data set from LHC Run I, and present prospects for LHC Run II.

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arXiv2014

Selectron NLSP in Gauge Mediation

We discuss gauge mediation models in which the smuon and the selectron are mass-degenerate co-NLSP, which we, for brevity, refer to as selectron NLSP. In these models, the stau, as well as the other superpartners, are parametrically heavier than the NLSP. We start by taking a bottom-up perspective and investigate the conditions under which selectron NLSP spectra can be realized in the MSSM. We then give a complete characterization of gauge mediation models realizing such spectra at low energies. The splitting between the slepton families is induced radiatively by the usual hierarchies in the Standard Model Yukawa couplings and hence, no new sources of flavour misalignment are introduced. We construct explicit weakly coupled messenger models which give rise to selectron NLSP, while accommodating a 126 GeV MSSM Higgs mass, both within the framework of General Gauge Mediation and in extensions where direct couplings between the messengers and the Higgs fields are present. In the latter class of models, large A-terms and relatively light stops can be achieved. The collider signatures of these models typically involve multilepton final states. We discuss the relevant LHC bounds and provide examples of models where the decay of the NLSP selectron is prompt, displaced or long-lived. The prompt case can be viewed as an ultraviolet completion of a simplified model recently considered by the CMS collaboration.

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arXiv2014

Bipartite Field Theories, Cluster Algebras and the Grassmannian

We review recent progress in Bipartite Field Theories. We cover topics such as their gauge dynamics, emergence of toric Calabi-Yau manifolds as master and moduli spaces, string theory embedding, relationships to on-shell diagrams, connections to cluster algebras and the Grassmannian, and applications to graph equivalence and stratification of the Grassmannian.

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arXiv2014

Multilepton signals of gauge mediated supersymmetry breaking at the LHC

We investigate multilepton LHC signals arising from electroweak processes involving sleptons. We consider the framework of general gauge mediated supersymmetry breaking, focusing on models where the low mass region of the superpartner spectrum consists of the three generations of charged sleptons and the nearly massless gravitino. We demonstrate how such models can provide an explanation for the anomalous four lepton events recently observed by the CMS collaboration, while satisfying other existing experimental constraints. The best fit to the CMS data is obtained for a selectron/smuon mass of around 145 GeV and a stau mass of around 90 GeV. These models also give rise to final states with more than four leptons, offering alternative channels in which they can be probed and we estimate the corresponding production rates at the LHC.

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arXiv2013

The Geometry of On-Shell Diagrams

The fundamental role of on-shell diagrams in quantum field theory has been recently recognized. On-shell diagrams, or equivalently bipartite graphs, provide a natural bridge connecting gauge theory to powerful mathematical structures such as the Grassmannian. We perform a detailed investigation of the combinatorial and geometric objects associated to these graphs. We mainly focus on their relation to polytopes and toric geometry, the Grassmannian and its stratification. Our work extends the current understanding of these connections along several important fronts, most notably eliminating restrictions imposed by planarity, positivity, reducibility and edge removability. We illustrate our ideas with several explicit examples and introduce concrete methods that considerably simplify computations. We consider it highly likely that the structures unveiled in this article will arise in the on-shell study of scattering amplitudes beyond the planar limit. Our results can be conversely regarded as an expansion in the understanding of the Grassmannian in terms of bipartite graphs.

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arXiv2013

Phenomenology of General Gauge Mediation in light of a 125 GeV Higgs

We explore the phenomenology of the full General Gauge Mediation parameter space in the MSSM focusing on the consequences of having a fundamental Higgs around 125 GeV. Assuming GUT-complete structure of the hidden sector, we allow for deviations from the strict definition of gauge mediated SUSY-breaking coming from mild violations of messenger-parity and from extra couplings between the Higgs multiplets and the hidden sector. Relaxing the GUT assumption, our parameter space is defined by the property of having vanishing A-terms at the messenger scale. In this extended setup we focus on the possibility of splitting the SU(3) mass parameters of GGM. In all these scenarios we investigate the possible spectra, discussing to what extent having an Higgs mass around 125 GeV is constraining the GGM parameter space and what are the possible signatures at LHC.

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arXiv2013

A Zig-Zag Index

We study the large N superconformal index of quiver gauge theories describing the worldvolume of D3 branes probing toric Calabi Yau singularities. The index has been previously noticed to factorize over the set of the extremal BPS mesonic operators of the gauge theory. We review this factorization and reformulate it in terms of zig-zag paths in the dimer model associated to the quiver. By using this reformulation, we argue that the factorization is valid not only for the exact R charge but for every set of R_{trial} respecting the marginality constraints. Moreover, we show the factorization of the index also in theories with orbifold singularities, previously not investigated. We conclude by providing an expression for the index in terms of the toric data of the dual geometry.

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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.

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arXiv2012

BPS states and their reductions

We develop a method to identify the BPS states in the Hilbert space of a supersymmetric field theory on a generic curved space which preserves at least two real supercharges. We also propose a one-to-one map between BPS states in d-dimensional field theories and states that contribute to the supersymmetric partition function of a corresponding (d-1)-dimensional field theory. As an application we obtain the superconformal index on rounded and squashed three spheres, and we show a natural reduction of the respective indices to the three-dimensional exact partition functions. We discuss the validity of the correspondence both at the perturbative and at the non-perturbative level and exploit the idea to uplift the computation of the exact supersymmetric partition function on a general manifold to a higher dimensional index.

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arXiv2012

Soft Spectrum in Yukawa-Gauge Mediation

We introduce a model independent parametrization for a subclass of gauge mediated theories, which we refer to as Yukawa-gauge mediation. Within this formalism we study the resulting soft masses in the visible spectrum. We find general expressions for the gaugino and scalar masses. Under generic conditions, the gaugino mass is screened, vanishing at first order in the SUSY breaking scale.

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arXiv2012

Collider signatures of goldstini in gauge mediation

We investigate the collider signatures of the multiple goldstini scenario in the framework of gauge mediation. This class of models is characterized by a visible sector (e.g. the MSSM or any extension) coupled by gauge interactions to more than one SUSY breaking sector. The spectrum consists of a light gravitino LSP, behaving as a goldstino, and a number of neutral fermions (the pseudo-goldstini) with a mass between that of the LSP and that of the lightest particle of the observable sector (LOSP). We consider the two situations where the LOSP is either a gaugino-like neutralino or a stau and we assume only one pseudo-goldstino of a mass of O(100) GeV. The coupling of the LOSP to the pseudo-goldstino can be enhanced with respect to those of the gravitino giving rise to characteristic signatures. We show that the decay modes of the LOSP into a SM particle and a pseudo-goldstino can be significant. For both LOSP scenarios we analyze (pseudo)-goldstini production at colliders. Compared to standard gauge mediation the final state spectrum is softer and more structured.

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arXiv2012

Integrability on the Master Space

It has been recently shown that every SCFT living on D3 branes at a toric Calabi-Yau singularity surprisingly also describes a complete integrable system. In this paper we use the Master Space as a bridge between the integrable system and the underlying field theory and we reinterpret the Poisson manifold of the integrable system in term of the geometry of the field theory moduli space.

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arXiv2011

Negative Refractive Index in Hydrodynamical Systems

We discuss the presence of exotic electromagnetic phenomena in systems with finite charge density which are described by hydrodynamics. We show that such systems generically have negative refractive index for low frequency electromagnetic waves, i.e. the energy flux and the phase velocity of the wave propagate in opposite directions. We comment on possible phenomenological applications, focusing on the Quark Gluon Plasma.

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arXiv2011

Negative Refraction and Superconductivity

We discuss exotic properties of charged hydrodynamical systems, in the broken superconducting phase, probed by electromagnetic waves. Motivated by general arguments from hydrodynamics, we observe that negative refraction, namely the propagation in opposite directions of the phase velocities and of the energy flux, is expected for low enough frequencies. We corroborate this general idea by analyzing a holographic superconductor in the AdS/CFT correspondence, where the response functions can be explicitly computed. We study the dual gravitational theory both in the probe and in the backreacted case. We find that, while in the first case the refractive index is positive at every frequency, in the second case there is negative refraction at low enough frequencies. This is in agreement with hydrodynamic considerations.

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arXiv2011

Pseudo-Goldstini in Field Theory

We consider two SUSY-breaking hidden sectors which decouple when their respective couplings to the visible particles are switched off. In such a scenario one expects to find two light fermions: the Goldstino and the pseudo-Goldstino. While the former remains massless in the rigid limit, the latter becomes massive due to radiative effects which we analyze from several different points of view. This analysis is greatly facilitated by a version of the Goldberger-Treiman relation, which allows us to write a universal non-perturbative formula for the mass. We carry out the analysis in detail in the context of gauge mediation, where we find that the pseudo-Goldstino mass is at least around the GeV scale and can be easily at the electroweak range, even in low scale models. This leads to interesting and unconventional possibilities in collider physics and it also has potential applications in cosmology.

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arXiv2010

Unscreening the Gaugino Mass with Chiral Messengers

Gaugino screening, the absence of next-to-leading order corrections to gaugino masses, is a generic feature of gauge mediation models of supersymmetry breaking. We show that in a specific class of models, known as semi-direct gauge mediation, it is possible to avoid gaugino screening by allowing for a chiral messenger sector. Messengers then acquire a mass at some scale, for instance by higgsing or by some auxiliary strong coupling dynamics. We implement this idea in a simple model which we work out explicitly.

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