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Abstract A (toy) model for cold and luke-warm strongly-coupled nuclear matter at finite baryon density, is used to study neutrino transport. The complete charged current two-point correlators are computed in the strongly-coupled medium and their impact on neutrino transport is analyzed. The full result is compared with various approximations for the current correlators and the distributions, including the degenerate approximation, the hydrodynamic approximation as well as the diffusive approximation and we comment on their successes. Further improvements are discussed.

Abstract The single baryon solution of V-QCD is numerically computed. The spectrum of spin and isospin modes is also computed by quantizing the light fluctuations around the baryon. It is shown that there is a partial restoration of chiral symmetry at the baryon center.

Abstract We consider three related topics: (a) Holographic quantum field theories on AdS spaces. (b) Holographic interfaces of flat space QFTs. (c) Wormholes connecting generically different QFTs. We investigate in a concrete example how the related classical solutions explore the space of QFTs and we construct the general solutions that interpolate between the same or different CFTs with arbitrary couplings. The solution space contains many exotic flow solutions that realize unusual asymptotics, as boundaries of different regions in the space of solutions. We find phenomena like “walking” flows and the generation of extra boundaries via flow fragmentation.

Abstract The structure of the five-dimensional Tachyon-Chern-Simons action and its relevance to single-baryon states in the context of the V-QCD models for holographic QCD with backreacting flavor are analyzed. The most general form of the Tachyon-Chern-Simons 5-form, compatible with symmetries and flavor anomalies is determined. It is the sum of a non-trivial gauge-invariant 5-dimensional form and a non-invariant closed 5-form that reproduces the flavor anomalies. Single-baryon solutions of the gravity theory, arising from the DBI plus Tachyon-Chern-Simons actions are considered. The baryon is realised as a bulk axial instanton. The baryon ansatz and the field equations are derived and the boundary conditions are determined, which ensure that the solution has finite boundary energy and unit baryon charge. The boundary baryon number, which is computed from the universal (closed) part of the Tachyon-Chern-Simons action, is shown to coincide with the bulk axial instanton number.

Abstract Holographic RG flows dual to QFTs on a squashed S 3 are considered in the framework of Einstein dilaton gravity in four dimensions. A general dilaton potential is used and flows are driven by a scalar relevant operator. The general properties of such flows are analysed and the UV and IR asymptotics are computed. Exotic asymptotics are found, that are different from the standard Fefferman-Graham asymptotics.

Abstract We consider a class of tripartite systems for which two d-dimensional QFTs are cross-coupled via a third d + 1-dimensional “messenger” QFT. We analyse in detail the example of a pair of one-dimensional matrix quantum mechanics) coupled via a two­dimensional theory of the BF-type and compute its partition function and simple correlators. This construction is extendible in higher dimensions) using a Chern-Simons “messenger” theory. In all such examples, the exact partition function acquires a form, speculated to correspond to systems dual to Euclidean wormholes and the cross correlators are sufficiently soft and consistent with analogous gravitational calculations. Another variant of the tripartite system is studied, where the messenger theory is described by a non-self-interacting (matrix)-field, reaching similar conclusions. While the Euclidean theories we consider are perfectly consistent, the two possible analytic continuations into Lorentzian signature (messenger vs. boundary QFT directions) of the tripartite models, reveal physical features and “pathologies” resembling those of the expected Lorentzian gravitational backgrounds.

Abstract Hidden theories coupled to the SM may provide emergent (dark) vectors, that are composites/bound-states of the hidden fields. This is motivated by paradigms emerging from the AdS/CFT correspondence but it is a more general phenomenon. We explore the general setup and find that UV interactions among currents or charged fields give rise to emergent vectors in the IR. We study the general properties of such vectors and argue that they can be generically different from fundamental dark photons that have been studied so far.

Abstract Hidden theories coupled to the SM may provide emergent axions, that are composites/bound-states of the hidden fields. This is motivated by paradigms emerging from the AdS/CFT correspondence but it is a more general phenomenon. We explore the general setup and find that UV-sourced interactions of instanton densities give rise to emergent axions in the IR. We study the general properties of such axions and argue that they are generically different from both fundamental and composite axions that have been studied so far.

Abstract Asymptotically AdS wormhole solutions are considered in the context of holography. Correlation functions of local operators on distinct boundaries are studied. It is found that such correlators are finite at short distances. Correlation functions of non-local operators (Wilson loops) on distinct boundaries are also studied, with similar conclusions. Deformations of the theory with multi-trace operators on distinct boundaries are considered and studied. As a consequence of these results, the dual theory is expected to factorize in the UV, and the two sectors to be coupled by a soft non-local interaction. A simple field theory model with such behavior is presented.

Abstract We study F-functions in the context of field theories on S 3 using gauge-gravity duality, with the radius of S 3 playing the role of RG scale. We show that the on-shell action, evaluated over a set of holographic RG flow solutions, can be used to define good F-functions, which decrease monotonically along the RG flow from the UV to the IR for a wide range of examples. If the operator perturbing the UV CFT has dimension Δ > 3/2 these F -functions correspond to an appropriately renormalized free energy. If instead the perturbing operator has dimension Δ < 3/2 it is the quantum effective potential, i.e. the Legendre transform of the free energy, which gives rise to good F-functions. We check that these observations hold beyond holography for the case of a free fermion on S 3 (Δ = 2) and the free boson on S 3 (Δ = 1), resolving a long-standing problem regarding the non-monotonicity of the free energy for the free massive scalar. We also show that for a particular choice of entangling surface, we can define good F-functions from an entanglement entropy, which coincide with certain F-functions obtained from the on-shell action.

Abstract Maximally symmetric curved-brane solutions are studied in dilatonic braneworld models which realise the self-tuning of the effective four-dimensional cosmological constant. It is found that no vacua in which the brane has de Sitter or anti-de Sitter geometry exist, unless one modifies the near-boundary asymptotics of the bulk fields. In the holographic dual picture, this corresponds to coupling the UV CFT to a curved metric (possibly with a defect). Alternatively, the same may be achieved in a flat-space QFT with suitable variable scalar sources. With these ingredients, it is found that maximally symmetric, positive and negative curvature solutions with a stabilised brane position generically exist. The space of such solutions is studied in two different types of realisations of the self-tuning framework. In some regimes we observe a large hierarchy between the curvature on the brane and the boundary UV CFT curvature. This is a dynamical effect due to the self-stabilisation mechanism. This setup provides an alternative route to realising de Sitter space in string theory.

Abstract Holographic RG flows dual to QFTs on maximally symmetric curved manifolds (dS d , AdS d , and S d ) are considered in the framework of Einstein-dilaton gravity in d + 1 dimensions. A general dilaton potential is used and the flows are driven by a scalar relevant operator. The general properties of such flows are analyzed and the UV and IR asymptotics computed. New RG flows can appear at finite curvature which do not have a zero curvature counterpart. The so-called ‘bouncing’ flows, where the β-function has a branch cut at which it changes sign, are found to persist at finite curvature. Novel quantum first-order phase transitions are found, triggered by a variation in the d-dimensional curvature in theories allowing multiple ground states.

Input from QCD and string theory is used in order to elucidate basic features of the string theory dual of QCD, It is argued that the relevant string theory is a fivedimensional version of the type0 superstring. The vacuum solution is asymptotically AdS5, and the geometry near the boundary is stringy. The structure of YM perturbation theory however emerges near the boundary. In the IR, the theory is argued to be wellapproximated by a twoderivative truncation that takes into account strong coupling effects. This explains the success of previously proposed fivedimensional Eisteindilaton gravity with an appropriate potential to describe salient features of the strong YM dynamics. [ABSTRACT FROM AUTHOR]

The question of graviton cloning in the context of the bulk/boundary correspondence is considered. It is shown that multi-graviton theories can be obtained from products of large-N CFTs. No more than one interacting massless graviton is possible. There can be however, many interacting massive gravitons that can be arbitrarily light. This is achieved by coupling CFTs via multi-trace marginal or relevant perturbations. The geometrical structure of the gravitational duals of such theories is that of product manifolds with their boundaries identified. The interpretation of such theories is discussed. Potential applications to massive gravity and cosmology are briefly suggested. [ABSTRACT FROM AUTHOR]

According to the inflationary theory of cosmology, most elementary particles in the current Universe were created during a period of reheating after inflation. In this Letter, we self-consistently couple the Einstein-inflaton equations to a strongly coupled quantum field theory as described by holography. We show that this leads to an inflating universe, a reheating phase, and finally a universe dominated by the quantum field theory in thermal equilibrium.

The thermodynamics of 5D dilaton gravity duals to confining gauge theories is analyzed. We show that they exhibit a first order Hawking-Page type phase transition. In the explicit background of improved holographic QCD of [U. Gursoy and E. Kiritsis, J. High Energy Phys. 02 (2008) 03210.1088/1126-6708/2008/02/032] [U. Gursoy, E. Kiritsis, and F. Nitti, J. High Energy Phys. 02 (2008) 01910.1088/1126-6708/2008/02/019], we find T&#95;{c}=235 MeV. The temperature dependence of various thermodynamic quantities such as the pressure, entropy, and speed of sound is calculated. The results are in agreement with the corresponding lattice data.