arXiv subjects

Stefano Bolognesi

Publications and source records attributed to Stefano Bolognesi.

At least 73 records · Page 4Linked to original sources

arXiv2012

Holographic Dual of the Lowest Landau Level

We describe the lowest Landau level of a quantum electron star in AdS4. In the presence of a suitably strong magnetic field, the dynamics of fermions in the bulk is effectively reduced from four to two dimensions. These two-dimensional fermions can subsequently be treated using the techniques of bosonization and the difficult many-body problem of building a gravitating, charged quantum star is reduced to solving the sine-Gordon model coupled to a gauge field and a metric. The kinks of the sine-Gordon model provide the holographic dual of the lowest Landau levels of the strongly-coupled d=2+1 dimensional boundary field theory. The system exhibits order one oscillations in the magnetic susceptibility, now arising as a classical effect in the bulk. Moreover, as the chemical potential is varied, we find jumps in the charge density, oscillations in the fractionalised charge density and plateaux in the cohesive charge density

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arXiv2012

A Gapless Hard Wall: Magnetic Catalysis in Bulk and Boundary

We study various aspects of fermions and their chiral condensates, both in the bulk of AdS4 spacetime and in the dual boundary theory. For the most part, we focus on a geometry with an infra-red hard wall. We show that, contrary to common lore, there exist boundary conditions in which the hard wall gives rise to a discrete, but gapless, fermionic spectrum. In such a setting, the presence of a magnetic field induces a bulk fermion condensate which spontaneously breaks CP invariance. We develop the holographic dictionary between composite operators and show that this bulk condensate has the interpretation of boundary magnetic catalysis involving a double-trace operator. Finally, we explain how one can replace the hard wall with bulk magnetic monopoles. In such a framework, magnetic catalysis can be viewed as a consequence of the Callan-Rubakov effect.

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arXiv2012

Magnetic Catalysis in AdS4

We study the formation of fermion condensates in Anti de Sitter space. In particular, we describe a novel version of magnetic catalysis that arises for fermions in asymptotically AdS4 geometries which cap off in the infra-red with a hard wall. We show that the presence of a magnetic field induces a fermion condensate in the bulk that spontaneously breaks CP symmetry. From the perspective of the dual boundary theory, this corresponds to a strongly coupled version of magnetic catalysis in d=2+1.

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arXiv2011

Instanton Partons in 5-dim SU(N) Gauge Theory

The circle compactification of the 6-dim (2,0) superconformal theory of $A_{N-1}$ type leads the 5-dim SU(N) maximally supersymmetric gauge theory. Instanton solitons embody Kaluza-Klein modes and are conjectured to be composed of partonic constituents. We realize such a parton of 1/N instanton topological charge at the intersection of magnetic flux sheets. After a further compactification with nontrivial Wilson line expectation value, instantons or calorons have been shown to be split into fundamental monopoles of fractional instanton charge. In the symmetric phase with trivial Wilson line expectation value, BPS instanton partons emerge more concretely as nonabelian BPS monopoles of minimum charge allowed in Dirac quantization.

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arXiv2011

1/4 BPS String Junctions and $N^3$ Problem in 6-dim (2,0) Superconformal Theories

We explore 1/4 BPS objects in the Coulomb phase of the ADE-type 6-dim (2,0) superconformal theories. By using the previous work on the junctions of strings in 5-dim gauge theories and 6-dim superconformal theories, we count the number of 1/4 BPS objects, which are made of waves on selfdual strings and junctions of selfdual strings and show that for all cases the number matches exactly one third of the anomaly constant $c_G=d_G h_G$ which is the product of dimension $d_G$ and dual Coxeter number $h_G$. This suggests the long sought after $N^3$ degrees of freedom are these 1/4 BPS objects at least in the Coulomb phase.

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arXiv2010

Monopoles and Holography

We present a holographic theory in AdS_4 whose zero temperature ground state develops a crystal structure, spontaneously breaking translational symmetry. The crystal is induced by a background magnetic field, but requires no chemical potential. This lattice arises from the existence of 't Hooft-Polyakov monopole solitons in the bulk which condense to form a classical object known as a monopole wall. In the infra-red, the magnetic field is screened and there is an emergent SU(2) global symmetry.

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arXiv2009

On the Possibility of a Trans-Planckian Duality

We investigate the possibility of a trans-Planckian duality, which exchanges a manifold of events (space-time), with a manifold of momenta (energy-momentum). Gravity has a dual counter-part, that is, a geometric theory defined on the manifold of momenta. We provide a mathematical framework that can possibly realize this idea, and analyze its classical behaviour.

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arXiv2009

On The Problem of the Quantum Heterotic Vortex

We address the problem of non-Abelian super-QCD, with a Fayet-Iliopoulos term, as seen from the vortex worldsheet perspective. Together with the FI term $ξ$, also a mass $μ$ for the adjoint superfield $Φ$ enters in the game. This mass allows the interpolation between $\N=2$ and $\N=1$ super-QCD. While the phenomenology of the $\N=2$ case ($μ=0$) is pretty much understood, much remains to be clarified for the finite-$μ$ case. We distinguish, inside the parameter space spanned by the FI term and the mass $μ$, four different corners where some quantitative statements can be made. These are the regions where the strong dynamics can, in some approximation, be quantitatively analyzed. We focus in particular on two questions: 1) Is the quantum vortex BPS or non-BPS? 2) What is the phase of the internal non-Abelian moduli? We find that the answer to these questions strongly depends upon the choice of the linear term in the superpotential. We also try to explain what happens in the most unexplored, and controversial, region of parameters, that of the quantum heterotic vortex, where $Λ\ll \sqrtξ \ll μ$.

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arXiv2009

Skyrmions in Orientifold and Adjoint QCD

This is a review of recent developments regarding the Skyrmion sector of higher representation QCD. Ordinary QCD is a SU(n) gauge theory with n_f Dirac quarks in the fundamental representation. Changing the representation of quarks leads to different and interesting theories, which are not as well studied as ordinary QCD. In order to be able to have a consistent asymptotically free large n limit, we must limit ourselves to three cases: two-index representation (symmetric or anti-symmetric) and adjoint representation. Skyrmions of the low-energy effective Lagrangian shall be the main subject of this review. There are puzzling aspects, both in orientifold and adjoint QCD, regarding the identification of the Skyrmion and its quantum stability, that have not yet been understood. We shall explain these problems and the solution we proposed for them. The first part is dedicated to the two-index representation. Here the challenge is to identify the correct particle in the spectrum that has to be identified with the Skyrmion. It turns out not to be the simplest baryon (as in ordinary QCD) but a baryonic state with higher charge, precisely composed by n(n\pm 1)/2 quarks. Although not the simplest among the baryons, it is the one that minimizes the mass per unit of baryonic charge and thus is the most stable among them. The second part is devoted to the quarks in the adjoint representation. The task here assume a different perspective. We do not have a baryon charge, like in ordinary QCD. An important role is now played by a massive fermion that must be considered in the low-energy effective Lagrangian. Through this fermion, the Skyrmion acquires an anomalous fermionic number (-1)^F and, as a consequence, an odd relationship between the latter and its spin/statistic. This implies a Z_2 stability of the Skyrmion.

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arXiv2008

A Coincidence Problem: How to Flow from N=2 SQCD to N=1 SQCD

We discuss, and propose a solution for, a still unresolved problem regarding the breaking from $\N=2$ super-QCD to $\N=1$ super-QCD. A mass term $W=μ\Tr Φ^2 / 2$ for the adjoint field, which classically does the required breaking perfectly, quantum mechanically leads to a relevant operator that, in the infrared, makes the theory flow away from pure $\N=1$ SQCD. To avoid this problem, we first need to extend the theory from $\SU (n_c)$ to $\U (n_c)$. We then look for the quantum generalization of the condition $W^{\prime}(m)=0$, that is, the coincidence between a root of the derivative of the superpotential $W(ϕ)$ and the mass $m$ of the quarks. There are $2n_c -n_f$ of such points in the moduli space. We suggest that with an opportune choice of superpotential, that selects one of these coincidence vacua in the moduli space, it is possible to flow from $\N=2$ SQCD to $\N=1$ SQCD. Various arguments support this claim. In particular, we shall determine the exact location in the moduli space of these coincidence vacua and the precise factorization of the SW curve.

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arXiv2008

A Note on Chern-Simons Solitons - a type III vortex from the wall vortex

We study some properties of topological Chern-Simons vortices in 2 + 1 dimensions. As has already been understood in the past, in the large magnetic flux limit, they are well described by a Chern-Simons domain wall, which has been compactified on a circle with the symmetric phase inside and the asymmetric phase on the outside. Our goal is two-fold. First we want to explore how the tension depends on the magnetic flux discretized by the integer n. The BPS case is already known, but not much has been explored about the non-BPS potentials. A generic renormalizable potential has two dimensionless parameters that can be varied. Variation of only one of them lead to a type I and type II vortex, very similar to the Abrikosov-Nielsen-Olesen (ANO) case. Variation of both the parameters leads to a much richer structure. In particular we have found a new type of vortex, which is type I-like for small flux and then turns type II-like for larger flux. We could tentatively denote it a type III vortex. This results in a stable vortex with number of fluxes which can be greater than one. Our second objective is to study the Maxwell-Chern-Simons theory and and understand how the large n limit of the CS vortex is smoothly connected with the large n limit of the ANO vortex.

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arXiv2006

Baryons and Skyrmions in QCD with Quarks in Higher Representations

We study the baryonic sector of QCD with quarks in the two index symmetric or antisymmetric representation. The minimal gauge invariant state that carries baryon number cannot be identified with the Skyrmion of the low energy chiral effective Lagrangian. Mass, statistics and baryon number do not match. We carefully investigate the properties of the minimal baryon in the large N limit and we find that it is unstable under formation of bound states with higher baryonic number. These states match exactly with the properties of the Skyrmion of the effective Lagrangian.

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arXiv2006

Soliton Junctions in the Large Magnetic Flux Limit

We study the flux tube junctions in the limit of large magnetic flux. In this limit the flux tube becomes a wall vortex which is a wall of negligible thickness (compared to the radius of the tube) compactified on a cylinder and stabilized by the flux inside. This wall surface can also assume different shapes that correspond to soliton junctions. We can have a flux tube that ends on a wall, a flux tube that ends on a monopole and more generic configurations containing all three of them. In this paper we find the differential equations that describe the shape of the wall vortex surface for these junctions. We will restrict to the cases of cylindrical symmetry. We also solve numerically these differential equations for various kinds of junctions. We finally find an interesting relation between soliton junctions and dynamical systems.

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arXiv2006

Multi-monopoles and Magnetic Bags

By analogy with the multi-vortices, we show that also multi-monopoles become magnetic bags in the large n limit. This simplification allows us to compute the spectrum and the profile functions by requiring the minimization of the energy of the bag. We consider in detail the case of the magnetic bag in the limit of vanishing potential and we find that it saturates the Bogomol'nyi bound and there is an infinite set of different shapes of allowed bags. This is consistent with the existence of a moduli space of solutions for the BPS multi-monopoles. We discuss the string theory interpretation of our result and also the relation between the 't Hooft large n limit of certain supersymmetric gauge theories and the large n limit of multi-monopoles. We then consider multi-monopoles in the cosmological contest and provide a mechanism that could lead to their production.

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arXiv2005

Multi-vortices are Wall Vortices: A Numerical Proof

We study the Abrikosov-Nielsen-Olesen multi-vortices. Using a numerical code we are able to solve the vortex equations with winding number up to n=25,000. We can thus check the wall vortex conjecture previously made in hep-th/0507273 and hep-th/0507286. The numerical results show a remarkable agreement with the theoretical predictions.

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arXiv2005

Large N, Z_N Strings and Bag Models

We study Z_N strings in nonabelian gauge theories, when they can be considered as domain walls compactified on a cylinder and stabilized by the flux inside. To make the wall vortex approximation reliable, we must take the 't Hooft large N limit. Our construction has many points in common with the phenomenological bag models of hadrons.

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arXiv2005

Domain Walls and Flux Tubes

We present a new vortex solution made of a domain wall compactified into a cylinder and stabilized by the magnetic flux within. When the thickness of the wall is much less than the radius of the vortex some precise results can be obtained, such as the tension spectrum and profile functions. This vortex can naturally end on the wall that has created it, making the simplest junction between a wall and a vortex. We then classify every kind of junction between a flux tube and domain wall. The criteria for classification are as follows: a flux can or can not end on the wall, and when it ends, the flux must go somewhere. Various examples are discussed, including abelian and non-ablelian theories, as well as supersymmetric and non-supersymmetric theories.

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arXiv2005

Stable vs Unstable Vortices in SQCD

We give a topological classification of stable and unconfined massive particles and strings (and some instantons) in worldvolume theories of M5-branes and their dimensional reductions, generalizing Witten's classification of strings in SYM. In particular 4d N=2 SQCD softly broken to N=1 contains torsion (Douglas-Shenker) Z_N-strings and nontorsion (Hanany-Tong) Z-strings. Some of the former are stable when the flavor symmetry is gauged, while those that are not stable confine quarks and in some vacua even dyons into baryons. The nontorsion strings are stable if and only if all colors are locked to flavors, which is weaker than the BPS condition. As a byproduct unstable string decay modes and approximate lifetimes are found. Cascading theories have no vortices stabilized by the topological charges treated here and in particular Gubser-Herzog-Klebanov axionic strings do not carry such a charge.

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