Narrow Results

Scalar QFT on the boundary ℑ⁺ at future null infinity of a general asymptotically flat 4D spacetime is constructed using the algebraic approach based on Weyl algebra associated to a BMS-invariant symplectic form. The constructed theory turns out to be invariant under a suitable strongly-continuous unitary representation of the BMS group with manifest meaning when the fields are interpreted as suitable extensions to ℑ⁺ of massless minimally coupled fields propagating in the bulk. The group theoretical analysis of the found unitary BMS representation proves that such a field on ℑ⁺ coincides with the natural wave function constructed out of the unitary BMS irreducible representation induced from the little group Δ, the semidirect product between SO(2) and the two-dimensional translations group. This wave function is massless with respect to the notion of mass for BMS representation theory. The presented result proposes a natural criterion to solve the long-standing problem of the topology of BMS group. Indeed the found natural correspondence of quantum field theories holds only if the BMS group is equipped with the nuclear topology rejecting instead the Hilbert one. Eventually, some theorems towards a holographic description on ℑ⁺ of QFT in the bulk are established at level of C*-algebras of fields for asymptotically flat at null infinity spacetimes. It is proved that preservation of a certain symplectic form implies the existence of an injective *-homomorphism from the Weyl algebra of fields of the bulk into that associated with the boundary ℑ⁺. Those results are, in particular, applied to 4D Minkowski spacetime where a nice interplay between Poincaré invariance in the bulk and BMS invariance on the boundary at null infinity is established at the level of QFT. It arises that, in this case, the *-homomorphism admits unitary implementation and Minkowski vacuum is mapped into the BMS invariant vacuum on ℑ⁺.

The two surprising features of gravity are (a) the principle of equivalence and (b) the connection between gravity and thermodynamics. Using principle of equivalence and special relativity in the local inertial frame, one could obtain the insight that gravity must possess a geometrical description. We show that, using the same principle of equivalence, special relativity and quantum theory in the local Rindler frame one can obtain the Einstein–Hilbert action functional for gravity and thus the dynamics of the space–time. This approach, which essentially involves postulating that the horizon area must be proportional to the entropy, uses the local Rindler frame as a natural extension of the local inertial frame and leads to the interpretation that the gravitational action represents the free energy of the space–time geometry. As an aside, one also obtains a natural explanation as to: (i) why the covariant action for gravity contains second derivatives of the metric tensor and (ii) why the gravitational coupling constant is positive. The analysis suggests that gravity is intrinsically holographic and even intrinsically quantum mechanical.

We consider issues related to tachyonic inflation with inverse-power-law potential. We find the solution of the evolution equations in the slow-roll limit in FRW as well as in the brane cosmology. Using the holographic entropy bound, we estimate the quantum-gravitational discreteness of tachyonic inflation perturbations.

In the Penrose limit, AdS×S space turns into a Cahen–Wallach (CW) space whose Killing vectors satisfy a Heisenberg algebra. This algebra is mapped onto the holographic screen on the boundary of AdS. We show that the Heisenberg algebra on the boundary of AdS may be obtained directly from the CW space by appropriately constraining the states defined on it. The transformations generated by the constraint are similar to gauge transformations. The "holographic screen" on the CW space is thus obtained as a "gauge-fixing" condition.

We investigate the geodesic motion in D-dimensional Majumdar–Papapetrou multi-black hole spacetimes and find that the qualitative features of the D = 4 case are shared by the higher dimensional configurations. The motion of timelike and null particles is chaotic, the phase space being divided into basins of attraction which are separated by a fractal boundary, with a fractal dimension d_B. The mapping of the geodesic trajectories on a screen placed in the asymptotic region is also investigated. We find that the fractal properties of the phase space induces a fractal structure on the holographic screen, with a fractal dimension d_B - 1.

We perform the first study of baryons in holographic QCD with multi-D-brane system in type IIA superstring theory. The baryon is described as a chiral soliton solution in the four-dimensional meson effective action derived from holographic QCD. We also present a brief review of the holographic model from the viewpoints of recent hadron physics and QCD phenomenologies.

We review 5D holographic approaches to finite temperature QCD. Thermodynamic properties of the "hard-wall" and the "soft-wall" models are derived. Various non-realistic features in these models are rectified by the setup of improved holographic QCD, that we review here.

Gravitational theories including negative cosmological constant, dilaton and gauge fields are explored in higher dimensions, in which black hole solutions are shown to exist and their asymptotic behaviors are obtained. Based on these solutions, effective Randall–Sundrum brane worlds are constructed. In the framework of gauge/gravity duality, effects from cosmological constant on the spectra of standard model fields on the branes are perturbatively calculated.

It is possible to provide a physical interpretation for the field equations of gravity based on a thermodynamical perspective. The virtual degrees of freedom associated with the horizons, as perceived by the local Rindler observer, play a crucial role in this approach. In this context, the relation S = E/2T between the entropy (S), active gravitational mass (E) and temperature (T) — obtained previously in gr-qc/0308070 [CQG, 21, 4485 (2004)] — can be reinterpreted as the law of equipartition E = (1/2) nk_BT where is the number (density) of microscopic horizon degrees of freedom in an area ΔA. Conversely, one can use the equipartition argument to provide a thermodynamic interpretation of gravity, even in the nonrelativistic limit. These results emphasize the intrinsic quantum nature of all gravitational phenomena and diminishes the distinction between thermal phenomena associated with local Rindler horizons and the usual thermodynamics of macroscopic bodies in non-inertial frames. Just like the original thermodynamic interpretation, these results also hold for a wide class of gravitational theories like the Lanczos–Lovelock models.

We calculate the static Wilson loop from string/gauge correspondence to obtain the potential in nonrelativistic quantum field theory, i.e. CFT with Galilean symmetry. We analyze the convexity conditions¹³ for potential in this theory, and obtain restrictions for the acceptable dynamical exponent z.

We construct a gravity dual for scale invariant but non-conformal field theories with a cyclic renormalization group flow. A slight modification of our construction gives a gravity dual of discretely scale invariant field theories. The underlying gravitational theory breaks the null energy condition.

We consider backreacted $Ad{S}_5\times S^5$ coupled with $N_f$ massive flavors introduced by D7 branes. The backreacted geometry is in the Veneziano limit with fixed $N_f/N_c$. By dividing one of the directions into a line segment with length l, we get two subspaces. Then we calculate the entanglement entropy between them. With the method of [I. R. Klebanov, D. Kutasov and A. Murugan, Nucl. Phys. B796, 274 (2008)], we are able to find the cut-off independent part of the entanglement entropy and finally find that this geometry shows no confinement/deconfinement phase transition at zero temperature from the holographic entanglement entropy point of view similar to the case in pure $Ad{S}_5\times S^5$.

In holography, there is a one-to-one correspondence between physical observables in the bulk and boundary theories. To define physical observables, however, regularization needs to be implemented in both sides of the correspondence. It is arguable whether the correspondence should extend to regularization and renormalization scheme which are not physical in the conventional sense. However, if we are to take the renormalization group (RG) interpretation of holography seriously, its precise understanding appears to require the matching of regularizations and renormalization schemes in the bulk and boundary theories. We address this question in the AdS₅/CFT₄ correspondence by considering the simplest physical quantity, the Casimir energy of the ${𝒩}=4$ super Yang–Mills (SYM) theory on $ℝ\times S^3$, in a $\zeta$-function regularization and show that there are choices of scheme which match the bulk AdS result, including the radial cutoff-dependent corrections when the cutoff is kept finite. We further discuss the implication of this result to the RG interpretation of holography.

We provide a brief summary of a method to calculate improvements to the Veneziano amplitude, creating sub-leading nonlinearities in the Regge trajectory of states. We formulate it as an extension of a computation by Makeenko and Olesen. We begin in a confining gauge theory coupled to matter, rewriting the meson scattering amplitude as a specific path integral over shapes and sizes of closed Wilson loops using the worldline formalism. We then prescribe how to further the computation at strong coupling by employing holography, which provides a prescription for the expectation value of these Wilson loops in strongly coupled regimes. The computation we desire then appears to subsume to a certain calculation in the effective field theory of a string worldsheet embedded in a certain broad class of allowed holographic backgrounds. A convenient interaction picture presents itself naturally in this context, allowing us to draw Feynman diagrams corresponding to the first few corrections due to weaker coupling regimes. The answer we find has qualitatively the same features as other endeavors with the same objective.

We study the fermionic spectrum with Weyl correction, which exhibits the non-Fermi liquid behavior. Also, we find that both the height of the peak of the fermionic spectrum and the dispersion relation exhibit a nonlinearity with the variety of the Weyl coupling parameter $\gamma$, which means that such nonlinearity may be ascribed to one of the Maxwell field. Another important property of this system is that for $\gamma <0$, the degree of the deviation from Fermi liquid is heavier than that for $\gamma >0$. It indicates that there is a transition of coupling strength in the dual boundary field theory.

We compute the quantum information metrics of a thermal CFT on ${ℝ}^{1,1}$ perturbed by the scalar primary operators of conformal dimensions $\mathrm{\Delta }$ = 3, 4, 5, 6. In particular, we assume that the Hamiltonians of the mixed states commute with each other and the temperature is fixed. Under these conditions, the evaluation is analogous to the pure state case. Then we apply the method of A. Trivella [Class. Quantum Grav.34, 105003 (2017)] to calculate the mixed state information metric for the scalar primary operator of conformal dimension $\mathrm{\Delta }$ = 4 holographically, and reproduce exactly the result in the CFT₂ by our approach.

In this paper, we use the complexity equals action proposal and investigate holographic complexity for hyperscaling violating theories on different subregions of space-time enclosed by the null boundaries. We are interested in computing the onshell action for certain subregions of the intersection between the Wheeler DeWitt patch and the past, as well as, the future interior of a two-sided black brane. More precisely, we extend the results of Ref. 1 in parts, to hyperscaling violating geometries and to find the finite onshell action, we define the proper counter terms. We show that in computing the rate of complexification the dynamical exponent plays a crucial rule, but, at the late time, rate of the complexity growth is independent of the hyperscaling parameters.

We propose to describe the gauge sector of an asymptotically safe field theory in $d=4-𝜖$ dimensions as a scalar theory on fixed AdS in $(d+1)$-dimensions using the holographic dictionary.

In this paper, we construct a new charged AdS black hole with modified cosmic Chaplygin gas (MCCG). In comparison to the previous model (modified Chaplygin AdS black hole) that existed in the literature, we now have two new parameters: the cosmic parameter and the black hole’s electric charge. We examine the asymptotically charged AdS black hole thermodynamics with MCCG under the assumption of a negative cosmological constant as a thermodynamics pressure. Using MCCG, we developed a new solution to Einstein’s AdS black hole field equations. The mass parameter, volume, electric potential, entropy, and temperature of the charged AdS black hole have all been computed. We also study the various energy conditions for the MCCG as a source fluid of AdS black hole. For some restrictions on the involved parameters, we show that these conditions are met. Then, we study the thermodynamical stability, critical points, and Joule-Thompson expansion for the back hole obtained. We reveal that while the existence of cosmic parameter yields to a complete stable mode, its absence gives rise to some unstable regions. Then, using MCCG, we treat the obtained black hole’s thermodynamics as a heat engine and calculate the work done as well as the heat engine’s maximum efficiency in the Carnot cycle. The work done, the efficiency, and the Rankine cycle’s efficiency are also investigated. All of the findings are graphically depicted and discussed.

In earlier work, the evolution operator for the exact RG equation was mapped to a field theory in Euclidean AdS. This gives a simple way of understanding AdS/CFT. We explore aspects of this map by studying a simple example of a Schrödinger equation for a free particle with time-dependent mass. This is an analytic continuation of an ERG like equation. We show for instance that it can be mapped to a harmonic oscillator. We show that the same techniques can lead to an understanding of dS/CFT too.