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Badreddine Benhellal

Publications and source records attributed to Badreddine Benhellal.

10 recordsLinked to original sources
arXiv2026

MIT bag model and infinite mass limit in non-smooth domains

The work is devoted to the study of Dirac operators with MIT bag boundary conditions in Euclidean domains with compact Lipschitz boundaries in arbitrary dimensions. It is shown that such operators are self-adjoint on suitable definition domains and can be recovered as the norm-resolvent limits of Dirac operators in the whole space with a large mass term outside the domain, under the assumption that an associated Robin-Laplacian eigenvalue has a prescribed asymptotic behavior with respect to a parameter in the boundary condition. This assumption is shown to hold for a class of non-smooth domains, which includes convex domains and, more generally, domains that can be "locally convexified" by suitable diffeomorphisms. To the best of our knowledge, this represents the first infinite mass interpretation for the MIT bag model in the sense of resolvent convergence for non-smooth domains. Most results are extended to the generalized MIT bag boundary conditions with the help of the recently established congruence transform.

math.AP↗
arXiv2026

The Landau-Dirac operator with shell interactions: self-adjointness and clustering

We consider the two-dimensional Dirac operator with constant magnetic field that is perturbed by a combination of electrostatic and Lorentz-scalar delta interactions with variable coefficients supported on a smooth closed curve. Self-adjointness is studied in the so called non critical and critical cases. In the non-critical case the essential spectrum is unchanged - it remains to be the set of the Landau-Dirac levels, the eigenvalues of infinite multiplicity of the unperturbed operator - while in the critical case an additional interval of essential spectrum emerges in the spectral gap containing zero. Our main result concerns the discrete spectrum in the non-critical case: using the pseudodifferential properties of the involved boundary integral operators, we show that the eigenvalues accumulate at each Landau-Dirac level at a rate governed by the logarithmic capacity of the curve. A novel and surprising phenomenon is the change in the side of the accumulation depending on the position relative to the critical value. As a byproduct, clusters of eigenvalues for a family of exterior boundary value problems are obtained via confining couplings; the infinite-mass boundary condition arises as a special case.

math-ph↗
arXiv2025

Eigenvalue asymptotics for strong $\delta$-interactions supported on curves with corners

Let $\Gamma\subset\mathbb{R}^2$ be a piecewise smooth closed curve with corners. We discuss the asymptotic behavior of the individual eigenvalues of the two-dimensional Schr\"odinger operator $-\Delta-\alpha\delta_\Gamma$ for $\alpha\to\infty$, where $\delta_\Gamma$ is the Dirac $\delta$-distribution supported by $\Gamma$. It is shown that the asymptotics of several first eigenvalues is determined by the corner opening only, while the main term in the asymptotic expansion for the other eigenvalues is the same as for smooth curves. Under an additional assumption on the corners of $\Gamma$ (which is satisfied, in particular, if $\Gamma$ has no acute corners), a more detailed eigenvalue asymptotics is established in terms of a one-dimensional effective operator on the boundary.

math.SP↗
arXiv2023

On Neumann-Poincar\'e operators and self-adjoint transmission problems

We discuss the self-adjointness in $L^2$-setting of the operators acting as $-\nabla\cdot h\nabla$, with piecewise constant functions $h$ having a jump along a Lipschitz hypersurface $\Sigma$, without explicit assumptions on the sign of $h$. We establish a number of sufficient conditions for the self-adjointness of the operator with $H^s$-regularity for suitable $s\in[1,\frac{3}{2}]$, in terms of the jump value and the regularity and geometric properties of $\Sigma$. An important intermediate step is a link with Fredholm properties of the Neumann-Poincar\'e operator on $\Sigma$, which is new for the Lipschitz setting.

math.SP↗
arXiv2022

Curvature contribution to the essential spectrum of Dirac operators with critical shell interactions

We discuss the spectral properties of three-dimensional Dirac operators with critical combinations of electrostatic and Lorentz scalar shell interactions supported by a compact smooth surface. It turns out that the criticality of the interaction may result in a new interval of essential spectrum. The position and the length of the interval are explicitly controlled by the coupling constants and the principal curvatures of the surface. This effect is completely new compared to lower dimensional critical situations or special geometries considered up to now, in which only a single new point in the essential spectrum was observed.

math.SP↗
arXiv2022

A Poincar\'e-Steklov map for the MIT bag model

The purpose of this paper is to introduce and study Poincar\'e-Steklov (PS) operators associated to the Dirac operator $D_m$ with the so-called MIT bag boundary condition. In a domain $\Omega\subset\mathbb{R}^3$, for a complex number $z$ and for $U_z$ a solution of $(D_m-z)U_z=0$, the associated PS operator maps the value of $\Gamma_- U_z$, the MIT bag boundary value of $U_z$, to $\Gamma_+ U_z$, where $\Gamma_\pm$ are projections along the boundary $\partial\Omega$ and $(\Gamma_ - + \Gamma_+) = t_{\partial\Omega}$ is the trace operator on $\partial\Omega$. In the first part of this paper, we show that the PS operator is a zero-order pseudodifferential operator and give its principal symbol. In the second part, we study the PS operator when the mass $m$ is large, and we prove that it fits into the framework of $1/m$-pseudodifferential operators, and we derive some important properties, especially its semiclassical principal symbol. Subsequently, we apply these results to establish a Krein-type resolvent formula for the Dirac operator $H_M= D_m+ M\beta 1_{\mathbb{R}^3\setminus\overline{\Omega}}$ for large masses $M>0$, in terms of the resolvent of the MIT bag operator on $\Omega$. With its help, the large coupling convergence with a convergence rate of $\mathcal{O}(M^{-1})$ is shown.

math.AP↗
arXiv2021

Spectral Analysis of Dirac Operators with delta interactions supported on the boundaries of rough domains

Given an open set $\Omega\subset\mathbb{R}^3$. We deal with the spectral study of Dirac operators of the form $H_{a,\tau}=H+A_{a,\tau}\delta_{\partial\Omega}$, where $H$ is the free Dirac operator in $\mathbb{R}^3$, $A_{a,\tau}$ is a bounded invertible, self-adjoint operator in $\mathit{L}^{2}(\partial\Omega)^4$, depending on parameters $(a,\tau)\in\mathbb{R}\times\mathbb{R}^n$, $n\geqslant1$. We investigate the self-adjointness and the related spectral properties of $H_{a,\tau}$, such as the phenomenon of confinement and the Sobolev regularity of the domain in different situations. Our set of techniques, which is based on fundamental solutions and layer potentials, allows us to tackle the above problems under mild geometric measure theoretic assumptions on $\Omega$.

math.SP↗
arXiv2021

Spectral Properties of the Dirac Operator coupled with $\delta$-Shell Interactions

Let $\Omega\subset\mathbb{R}^3$ be an open set, we study the spectral properties of the free Dirac operator $\mathcal{H}$ coupled with the singular potential $V_\kappa=(\epsilon I_4 +\mu\beta+\eta(\alpha\cdot N))\delta_{\partial\Omega}$. The open set $\Omega$ can be either a $\mathcal{C}^2$-bounded domain or a locally deformed half-space. In both cases, self-adjointness is proved and several spectral properties are given. In particular, we give a complete description of the essential spectrum of $\mathcal{H}+V_\kappa$ for the so-called critical combinations of coupling constants, when $\Omega$ is a locally deformed half-space. Finally, we introduce a new model of Dirac operators with $\delta$-interactions and deals with its spectral properties. More precisely, we study the coupling $\mathcal{H}_{\upsilon}=\mathcal{H}+i\upsilon\beta(\alpha\cdot N)\delta_{\partial\Omega}$. In particular, we show that $\mathcal{H}_{\pm2}$ is essentially self-adjoint and generates confinement.

math.SP↗
arXiv2019

Spectral Asymptotic for the Infinite Mass Dirac Operator in bounded domain

In this paper, we study a singular perturbation of a problem used in dimension two to model graphene or in dimension three to describe the quark confinement phenomenon in hadrons. The operators we consider are of the form $H + M\beta V (x)$, where $H$ is the free Dirac operator, $\beta$ is a constant matrix, $V (x)$ is a real valued piecewise constant potential having a jump discontinuity across a smooth interface and $M$ is the mass that we can see as a coupling constant. In particular, we perform a complete asymptotic expansion of spectral quantities as the mass $M$ tends to $+\infty$.

math.SP↗