High Energy Physics Theory

We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results valid only at small magnetic fields. Surprisingly, at large magnetic field, we observe the appearance of two plasmon-like modes whose corresponding effective plasma frequency grows with the magnetic field and is not supported by any background charge density. Finally, we identify a mode collision which allows us to study the radius of convergence of the linearized hydrodynamics expansion as a function of the external magnetic field. We find that the radius of convergence in momentum space, related to the diffusive transverse electromagnetic mode, increases quadratically with the strength of the magnetic field.

Following Natanzon-Zabrodin, we explore the Kadomtsev-Petviashvili hierarchy as an infinite system of mutually consistent relations on the second derivatives of the free energy with some universal coefficients. From this point of view, various combinatorial properties of these coefficients naturally highlight certain non-trivial properties of the KP hierarchy. Furthermore, this approach allows us to suggest several interesting directions of the KP deformation via a deformation of these coefficients. We also construct an eigenvalue matrix model, whose correlators fully describe the universal KP coefficients, which allows us to further study their properties and generalizations.

Recently, [JHEP 20 131 (2020)] obtained (a similar, scaled version of) the (a,b)-phase diagram derived from the Kazakov--Zinn-Justin solution of the Hermitian two-matrix model with interactionsTr{a4(A4+B4)+b2ABAB},starting from Functional Renormalization. We comment on something unexpected: the phase diagram of [JHEP 20 131 (2020)] is based on aβb-function that does not have the one-loop structure of the Wetterich-Morris Equation. This raises the question of how to reproduce the phase diagram from a set ofβ-functions that is, in its totality, consistent with Functional Renormalization. A non-minimalist, yet simple truncation that could lead to the phase diagram is provided. Additionally, we identify the ensemble for which the result of op. cit. would be entirely correct.

String theory on AdS3with NS-NS fluxes admits a solvable irrelevant deformation which is close to theTT¯deformation of the dual CFT2. This consists of deforming the worldsheet action, namely the action of theSL(2,R)WZW model, by adding to it the operatorJ??J¯??, constructed with two Kac-Moody currents. The geometrical interpretation of the resulting theory is that of strings on a conformally flat background that interpolates between AdS3in the IR and a flat linear dilaton spacetime with Hagedorn spectrum in the UV, having passed through a transition region of positive curvature. Here, we study the properties of this string background both from the point of view of the low-energy effective theory and of the worldsheet CFT. We first study the geometrical properties of the semiclassical geometry, then we revise the computation of correlation functions and of the spectrum of theJ??J¯??-deformed worldsheet theory, and finally we discuss how to extend this type of current-current deformation to other conformal models.

We start from an attractive consideration of the negative cosmological constant of an AdS background as a thermodynamic positive pressure, to find some interesting thermodynamic comparisons between regular(Bardeen and Hayward)-AdS black holes in the extended phase space. It mainly shows as following: \textit{i)} the Hayward-AdS black hole with a magnetic charge and pressure constant is accommodate a smaller exist remnant mass; \textit{ii)} the Bardeen-AdS black hole has a smaller critical magnetic chargeQc; \textit{iii)} the Bardeen-AdS black hole always leaves a smaller zero temperature remnant. Meanwhile, it is surprising to discover that the Bardeen-AdS black hole is smaller than the Hayward-AdS black hole for the universal ratioε, which may indicate that the Hayward-AdS black hole with a magnetic charge and pressure constant is easier to produce phase transition in comparison with the Bardeen-AdS black hole. These interesting thermodynamic properties further show the subtle differences and relations between the structures of the Hayward-AdS and Bardeen-AdS black holes in the extended phase space.

We propose and investigate several complex versions of extensions and restrictions of the Skyrme model with a well-defined Bogomolny-Prasad-Sommerfield (BPS) limit. The models studied possess complex kink, anti-kink, semi-kink, massless and purely imaginary compacton BPS solutions that all have real energies. The reality of the energies for a particular solution is guaranteed when a modified antilinear CPT-symmetry maps the Hamiltonian functional to its parity time-reversed complex conjugate and the solution field to itself or a new field with degenerate energy. In addition to the known BPS Skyrmion configurations we find new types that we refer to as step, cusp, shell, and purely imaginary compacton solutions.

We use the SYK family of models withNMajorana fermions to study the complexity of time evolution, formulated as the shortest geodesic length on the unitary group manifold between the identity and the time evolution operator, in free, integrable, and chaotic systems. Initially, the shortest geodesic follows the time evolution trajectory, and hence complexity grows linearly in time. We study how this linear growth is eventually truncated by the appearance and accumulation of conjugate points, which signal the presence of shorter geodesics intersecting the time evolution trajectory. By explicitly locating such "shortcuts" through analytical and numerical methods, we demonstrate that: (a) in the free theory, time evolution encounters conjugate points at a polynomial time; consequently complexity growth truncates atO(N??????), and we find an explicit operator which "fast-forwards" the freeN-fermion time evolution with this complexity, (b) in a class of interacting integrable theories, the complexity is upper bounded byO(poly(N)), and (c) in chaotic theories, we argue that conjugate points do not occur until exponential timesO(eN), after which it becomes possible to find infinitesimally nearby geodesics which approximate the time evolution operator. Finally, we explore the notion of eigenstate complexity in free, integrable, and chaotic models.

We study notions of complexity for link complement states in Chern Simons theory with compact gauge groupG. Such states are obtained by the Euclidean path integral on the complement ofn-component links inside a 3-manifoldM3. For the Abelian theory at levelkwe find that a natural set of fundamental gates exists and one can identify the complexity as differences of linking numbers modulok. Such linking numbers can be viewed as coordinates which embeds all link complement states intoZ?�n(n??)/2kand the complexity is identified as the distance with respect to a particular norm. For non-Abelian Chern Simons theories, the situation is much more complicated. We focus here on torus link states and show that the problem can be reduced to defining complexity for a single knot complement state. We suggest a systematic way to choose a set of minimal universal generators for single knot complement states and then evaluate the complexity using such generators. A detailed illustration is shown forSU(2)kChern Simons theory and the results can be extended to general compact gauge group.

We derive the component structure of 11D,N=1/8supergravity linearized around eleven-dimensional Minkowski space. This theory represents 4 local supersymmetries closing onto 4 of the 11 spacetime translations without the use of equations of motion. It may be interpreted as adding201auxiliary bosons and56auxiliary fermions to the physical supergravity multiplet for a total of376+376components. These components and their transformations are organized into representations ofSL(2;C)?G2.

In a close look at the replica wormhole derivation of the island conjecture, we note a discrepancy in the derived matrix eigenvalues in the limit where the Hawking radiation entropy goes to zero. The small corrections to the density matrix for the radiation infer thattr(?2R), equally a sum over the eigenvalues squared, must be small (??) at all times. This is in contradiction with an ensemble dominated by a density matrix with an eigenvalue close to unity. Also, the radiation entropy has been approximated by the ensemble averaged entropy, as in a final state analysis. For?R=?R(?)with?the set of variables used in the average, the ensemble average is only an accurate estimate of the entropy after?has been measured. At the formation of each Hawking pair, there is a distribution over?that affects the entropy. Without a real time determination of?, the radiation entropy follows Hawking's result during the evaporation. A question remains of how quickly such determinations can be assumed to occur. A complete argument for that the radiation entropy follows the Page curve should address this.