8 research outputs found
Bending branes for DCFT in two dimensions
We consider a holographic dual model for defect conformal field theories
(DCFT) in which we include the backreaction of the defect on the dual geometry.
In particular, we consider a dual gravity system in which a two-dimensional
hypersurface with matter fields, the brane, is embedded into a
three-dimensional asymptotically Anti-de Sitter spacetime. Motivated by recent
proposals for holographic duals of boundary conformal field theories (BCFT), we
assume the geometry of the brane to be determined by Israel junction
conditions. We show that these conditions are intimately related to the energy
conditions for the brane matter fields, and explain how these energy conditions
constrain the possible geometries. This has implications for the holographic
entanglement entropy in particular. Moreover, we give exact analytical
solutions for the case where the matter content of the brane is a perfect
fluid, which in a particular case corresponds to a free massless scalar field.
Finally, we describe how our results may be particularly useful for extending a
recent proposal for a holographic Kondo model.Comment: 35 pages + appendices, 12 figures, v2: added references and a
paragraph on negative tension solutions, v3: updated reference
Quantum Quenches in a Holographic Kondo Model
We study non-equilibrium dynamics and quantum quenches in a recent
gauge/gravity duality model for a strongly coupled system interacting with a
magnetic impurity with spin. At large , it is convenient to write
the impurity spin as a bilinear in Abrikosov fermions. The model describes an
RG flow triggered by the marginally relevant Kondo operator. There is a phase
transition at a critical temperature, below which an operator condenses which
involves both an electron and an Abrikosov fermion field. This corresponds to a
holographic superconductor in AdS and models the impurity screening. We
study the time dependence of the condensate induced by quenches of the Kondo
coupling. The timescale for equilibration is generically given by the
lowest-lying quasinormal mode of the dual gravity model. This mode also governs
the formation of the screening cloud, which is obtained as the decrease of
impurity degrees of freedom with time. In the condensed phase, the leading
quasinormal mode is imaginary and the relaxation of the condensate is
over-damped. For quenches whose final state is close to the critical point of
the large phase transition, we study the critical slowing down and obtain
the combination of critical exponents . When the final state is exactly
at the phase transition, we find that the exponential ringing of the
quasinormal modes is replaced by a power-law behaviour of the form . This indicates the emergence of a discrete scale
invariance.Comment: 23 pages + appendices, 11 figure