46 research outputs found
Higgs/amplitude mode dynamics from holography
Second order phase transitions are universally driven by an order parameter which becomes trivial at the critical point. At the same time, collective excitations which involve the amplitude of the order parameter develop a gap which smoothly closes to zero at criticality. We develop analytical techniques to study this âHiggsâ mode in holographic systems which undergo a continuous phase transition at finite temperature and chemical potential. This allows us to study the linear response of the system at energy scales of the order of the gap. We express the Greenâs functions of scalar operators in terms of thermodynamic quantities and a single transport coefficient which we fix in terms of black hole horizon data
Black hole excited states from broken translations in Euclidean time
We prepare an excited finite temperature state in SYM by means
of a Euclidean path integral with a relevant deformation. The deformation
explicitly breaks imaginary-time translations along the thermal circle whilst
preserving its periodicity. We then study how the state relaxes to thermal
equilibrium in real time. Computations are performed using real-time AdS/CFT,
by constructing novel mixed-signature black holes in numerical relativity
corresponding to Schwinger-Keldysh boundary conditions. These correspond to
deformed cigar geometries in the Euclidean, glued to a pair of dynamical
spacetimes in the Lorentzian.
The maximal extension of the Lorentzian black hole exhibits a `causal
shadow', a bulk region which is spacelike separated from both boundaries. We
show that causal shadows are generic in path-integral prepared states where
imaginary-time translations along the thermal circle are broken.Comment: 22 pages, 12 figures V2: references adde
Thermal three-point functions from holographic Schwinger-Keldysh contours
We compute fully retarded scalar three-point functions of holographic CFTs at
finite temperature using real-time holography. They describe the nonlinear
response of a holographic medium under scalar forcing, and display single and
higher-order poles associated to resonant QNM excitations. This involves
computing the bulk-to-bulk propagator on a piecewise mixed-signature spacetime,
the dual of the Schwinger-Keldysh contour. We show this construction is
equivalent to imposing ingoing boundary conditions on a single copy of a black
hole spacetime, similar to the case of the two-point function. We also compute
retarded scalar correlators with stress-tensor insertions in general CFTs by
solving Ward identities on the Schwinger-Keldysh contour.Comment: 21 pages, 4 figures. Typo fixed and discussed FDT with bulk-bulk
propagator
Holographic dissipation from the symplectic current
We develop analytic techniques to construct the leading dissipative terms in a derivative expansion of holographic fluids. Our basic ingredient is the Crnkovic-Witten symplectic current of classical gravity which we use to extract the dissipative transport coefficients of holographic fluids, assuming knowledge of the thermodynamics and the near horizon geometries of the bulk black hole geometries. We apply our techniques to non-conformal neutral fluids to reproduce previous results on the shear viscosity and generalise a known expression for the bulk viscosity
Towards a holographic quark matter crystal
We construct the gravity dual of d = 4, N=4N=4 , SU(Nc) super Yang-Mills theory, coupled to Nf flavors of dynamical quarks, at non-zero temperature T and nonzero quark density Nq. The supergravity solutions possess a regular horizon if T > 0 and include the backreaction of Nc color D3-branes and Nf flavor D7-branes with Nq units of electric flux on their worldvolume. At zero temperature the solutions interpolate between a Landau pole singularity in the ultraviolet and a Lifshitz geometry in the infrared. At high temperature the thermodynamics is directly sensitive to the Landau pole, whereas at low temperature it is not, as expected from effective field theory. At low temperature and sufficiently high charge density we find thermodynamic and dynamic instabilities towards the spontaneous breaking of translation invariance
Three-dimensional super Yang-Mills with compressible quark matter
We construct the gravity dual of three-dimensional, SU(Nc) super Yang-Mills theory with Nf flavors of dynamical quarks in the presence of a non-zero quark density Nq. The supergravity solutions include the backreaction of Nc color D2-branes and Nf flavor D6-branes with Nq units of electric flux on their worldvolume. For massless quarks, the solutions depend non-trivially only on the dimensionless combination Ïâ=âNc2Nq/λ2Nf4, with λâ=âgYM2Nc the ât Hooft coupling, and describe renormalization group flows between the super Yang-Mills theory in the ultraviolet and a non-relativistic theory in the infrared. The latter is dual to a hyperscaling-violating, Lifshitz-like geometry with dynamical and hyperscaling-violating exponents z = 5 and Ξ = 1, respectively. If Ï âȘ 1 then at intermediate energies there is also an approximate AdS4 region, dual to a conformal Chern-Simons-Matter theory, in which the flow exhibits quasi-conformal dynamics. At zero temperature we compute the chemical potential and the equation of state and extract the speed of sound. At low temperature we compute the entropy density and extract the number of low-energy degrees of freedom. For quarks of non-zero mass Mq the physics depends non-trivially on Ï and MqNc/λNf