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1. Line defects in fermionic CFTs

   https://doi.org/10.1007/JHEP08(2023)224  

   Giombi, Simone; Helfenberger, Elizabeth; Khanchandani, Himanshu (August 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> We study line defects in the fermionic CFTs in the Gross-Neveu-Yukawa universality class in dimensions 2< d <4. These CFTs may be described as the IR fixed points of the Gross-Neveu-Yukawa (GNY) model ind= 4 −ϵ, or as the UV fixed points of the Gross-Neveu (GN) model, which can be studied using the largeNexpansion in 2< d <4. These models admit natural line defects obtained by integrating over a line either the scalar field in the GNY description, or the fermion bilinear operator in the GN description. We compute the beta function for the defect RG flow using both the epsilon expansion and the largeNapproach, and find IR stable fixed points for the defect coupling, thus providing evidence for a non-trivial IR DCFT. We also compute some of the DCFT observables at the fixed point, and check that theg-function associated with the circular defect is consistent with theg-theorem for the defect RG flow. 

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2. A plane defect in the 3d O(N) model

   https://doi.org/10.21468/SciPostPhys.15.3.090  

   Krishnan, Abijith; Metlitski, Max A (September 2023, SciPost Physics)

   It was recently found that the classical 3d O(N) model in the semi-infinite geometry can exhibit an “extraordinary-log” boundary universality class, where the spin-spin correlation function on the boundary falls off as < S(x) S(0)> ~ 1/ (log x)^q. This universality class exists for a range 2 ≤ N < Nc and Monte-Carlo simulations and conformal bootstrap indicate Nc > 3. In this work, we extend this result to the 3d O(N) model in an infinite geometry with a plane defect. We use renormalization group (RG) to show that in this case the extraordinary-log universality class is present for any finite N ≥ 2. We additionally show, in agreement with our RG analysis, that the line of defect fixed points which is present at infinite N is lifted to the ordinary, special (no defect) and extraordinary-log universality classes by 1/N corrections. We study the “central charge” a for the O(N) model in the boundary and interface geometries and provide a non-trivial detailed check of an a-theorem by Jensen and O’Bannon. Finally, we revisit the problem of the O(N) model in the semi-infinite geometry. We find evidence that at N = Nc the extraordinary and special fixed points annihilate and only the ordinary fixed point is left for N > Nc . 

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3. Broken conformal window

   https://doi.org/10.1007/JHEP04(2025)152  

   Kondo, Dan; Murayama, Hitoshi; Noether, Bea; Varier, Digvijay Roy (April 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We show that near the edges of the conformal window of supersymmetric SU(N_c) QCD, perturbed by Anomaly Mediated Supersymmetry Breaking (AMSB), chiral symmetry can be broken depending on the initial conditions of the RG flow. We do so by perturbatively expanding around Banks-Zaks fixed points and taking advantage of Seiberg duality. Interpolating between the edges of the conformal window, we predict that non-supersymmetric QCD breaks chiral symmetry up toN_f≤ 3N_c− 1, while we cannot say anything definitive forN_f≥ 3N_cat this moment. 

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4. Flowing to $$ \mathcal{N} $$ = 3 Chern-Simons-matter theory

   https://doi.org/10.1007/JHEP03(2020)100  

   Guarino, Adolfo; Tarrío, Javier; Varela, Oscar (March 2020, Journal of High Energy Physics)

   null (Ed.)

   A bstract New renormalisation group flows of three-dimensional Chern-Simons theories with a single gauge group SU( N ) and adjoint matter are found holographically. These RG flows have an infrared fixed point given by a CFT with $$ \mathcal{N} $$ N = 3 supersymmetry and SU(2) flavour symmetry. The ultraviolet fixed point is again described by a CFT with either $$ \mathcal{N} $$ N = 2 and SU(3) symmetry or $$ \mathcal{N} $$ N = 1 and G 2 symmetry. The gauge/gravity duals of these RG flows are constructed as domain-wall solutions of a gauged supergravity model in four dimensions that enjoys an embedding into massive IIA supergravity. A concrete RG flow that brings a mass deformation of the $$ \mathcal{N} $$ N = 2 CFT into the $$ \mathcal{N} $$ N = 3 CFT at low energies is described in detail. 

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5. Fermions in AdS and Gross-Neveu BCFT

   https://doi.org/10.1007/JHEP07(2022)018  

   Giombi, Simone; Helfenberger, Elizabeth; Khanchandani, Himanshu (July 2022, Journal of High Energy Physics)

   A bstract We study the boundary critical behavior of conformal field theories of interacting fermions in the Gross-Neveu universality class. By a Weyl transformation, the problem can be studied by placing the CFT in an anti de Sitter space background. After reviewing some aspects of free fermion theories in AdS, we use both large N methods and the epsilon expansion near 2 and 4 dimensions to study the conformal boundary conditions in the Gross-Neveu CFT. At large N and general dimension d , we find three distinct boundary conformal phases. Near four dimensions, where the CFT is described by the Wilson-Fisher fixed point of the Gross-Neveu-Yukawa model, two of these phases correspond respectively to the choice of Neumann or Dirichlet boundary condition on the scalar field, while the third one corresponds to the case where the bulk scalar field acquires a classical expectation value. One may flow between these boundary critical points by suitable relevant boundary deformations. We compute the AdS free energy on each of them, and verify that its value is consistent with the boundary version of the F-theorem. We also compute some of the BCFT observables in these theories, including bulk two-point functions of scalar and fermions, and four-point functions of boundary fermions. 

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