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Published: 2018-02-20T20:30:00-05:00

 



Entanglement entropy between virtual and real excitations in quantum electrodynamics. (arXiv:1802.06774v1 [hep-th])

The aim of this work is to introduce the entanglement entropy of real and virtual excitations of fermion and photon fields. By rewriting the generating functional of quantum electrodynamics theory as an inner product between quantum operators, it is possible to obtain quantum density operators representing the propagation of real and virtual particles. These operators are partial traces, where the degrees of freedom traced out are unobserved excitations. Then the Von Neumann definition of entropy can be applied to these quantum operators and in particular, for the partial traces taken over the internal or external degrees of freedom. A universal behavior is obtained for the entanglement entropy for different quantum fields at zero order in the coupling constant. In order to obtain numerical results at different orders in the perturbation expansion, the Bloch-Nordsieck model is considered, where it it shown that for some particular values of the electric charge, the von Neumann entropy increases or decreases with respect to the non-interacting case.




Quasi-Newtonian Cosmological Models in hScalar-Tensor Theories of Gravity. (arXiv:1802.06778v1 [gr-qc])

In this contribution, classes of shear-free cosmological dust models with irrotational fluid flows will be investigated in the context of scalar-tensor theories of gravity. In particular, the integrability conditions describing a consistent evolution of the linearised field equations of quasi-Newtonian universes are presented. We also derive the covariant density and velocity propagation equations of such models and analyse the corresponding solutions to these perturbation equations.




Functional Determinants of Radial Operators in $AdS_2$. (arXiv:1802.06789v1 [hep-th])

We study the zeta-function regularization of functional determinants of Laplace and Dirac-type operators in two-dimensional Euclidean $AdS_2$ space. More specifically, we consider the ratio of determinants between an operator in the presence of background fields with circular symmetry and the free operator in which the background fields are absent. By Fourier-transforming the angular dependence, one obtains an infinite number of one-dimensional radial operators, the determinants of which are easy to compute. The summation over modes is then treated with care so as to guarantee that the result coincides with the two-dimensional zeta-function formalism. The method relies on some well-known techniques to compute functional determinants using contour integrals and the construction of the Jost function from scattering theory. Our work generalizes some known results in flat space. The extension to conformal $AdS_2$ geometries is also considered. We provide two examples, one bosonic and one fermionic, borrowed from the spectrum of fluctuations of the holographic $\frac{1}{4}$-BPS latitude Wilson loop.




Semiclassical echo dynamics in the Sachdev-Ye-Kitaev model. (arXiv:1802.06796v1 [cond-mat.stat-mech])

The existence of a quantum butterfly effect in the form of exponential sensitivity to small perturbations has been under debate for a long time. Lately, this question gained increased interest due to the proposal to probe chaotic dynamics and scrambling using out-of-time-order correlators. In this work we study echo dynamics in the Sachdev-Ye-Kitaev model under effective time reversal in a semiclassical approach. We demonstrate that small imperfections introduced in the time-reversal procedure result in an exponential divergence from the perfect echo, which allows to identify a Lyapunov exponent $\lambda_L$. In particular, we find that $\lambda_L$ is twice the Lyapunov exponent of the semiclassical equations of motion. This behavior is attributed to the growth of an out-of-time-order double commutator that resembles an out-of-time-order correlator.




Corrections to Newton's law of gravitation - application to hybrid Bloch brane. (arXiv:1802.06808v1 [gr-qc])

We present in this work, the calculations of corrections in the Newton's law of gravitation due to Kaluza-Klein gravitons in five-dimensional warped thick braneworld scenarios. We consider here a recently proposed model, namely, the hybrid Bloch brane. This model couples two scalar fields to gravity and is engendered from a domain wall-like defect. Also, two other models the so-called asymmetric hybrid brane and compact brane are considered. As a matter of fact, these models are obtained from deformations of the phi4 and sine-Gordon topological defects. Then, we constructed the branes upon such defects, and the corresponding corrections in Newton's law of gravitation are computed. In order to attain the mass spectrum and its corresponding eigenfunctions which are the essential quantities for computing the correction to the Newtonian potential, we develop a suitable numerical technique.




Flat holography and Carrollian fluids. (arXiv:1802.06809v1 [hep-th])

We show that a holographic description of four-dimensional asymptotically flat spacetimes is reached smoothly from the zero-cosmological-constant limit of anti-de Sitter holography. To this end, we use the derivative expansion of fluid/gravity correspondence. From the boundary perspective, the vanishing of the bulk cosmological constant appears as the zero velocity of light limit. This sets how Carrollian geometry emerges in flat holography. The new boundary data are a two-dimensional spatial surface, identified with the null infinity of the bulk Ricci-flat spacetime, accompanied with an absolute time and equipped with a Carrollian structure, plus the dynamical observables of a conformal Carrollian fluid. These are the energy, the viscous stress tensors and the heat currents, whereas the Carrollian geometry is gathered by a two-dimensional spatial metric, a frame connection and a scale factor. The reconstruction of Ricci-flat spacetimes from Carrollian boundary data is conducted with a flat derivative expansion, resummed in a closed form under further integrability conditions inherited from the ancestor anti-de Sitter set-up. These conditions are hinged on a duality relationship among fluid friction tensors and Cotton-like geometric data. We illustrate these results in the case of conformal Carrollian perfect fluids and Robinson--Trautman viscous hydrodynamics. The former are dual to the asymptotically flat Kerr--Taub--NUT family, while the latter leads to the homonymous class of algebraically special Ricci-flat spacetimes.




Cuscuton Bounce. (arXiv:1802.06818v1 [gr-qc])

In general relativity producing a regular bounce entails violation of Null Energy Condition for a dynamical source in the model. That generically indicates existence of ghosts or other instabilities. However, in cuscuton modification of gravity, the correspondence between a background bounce and violation of Null Energy Condition for dynamical sources is broken. Cuscuton is an Infra Red modification and it can make the background go through a regular bounce. At the same time, since it does not contain any dynamical degrees of freedom, it does not lead to ghosts or other instabilities. Here, we present a toy scenario of a regular bouncing cosmology and prove this claim. Our model is presented as a proof of concept at this point and does not aim to explain observations in late time cosmology.




Magnetic monopoles in noncommutative quantum mechanics 2. (arXiv:1802.06854v1 [math-ph])

In this paper we extend the analysis of magnetic monopoles in quantum mechanics in three dimensional rotationally invariant noncommutative space $\textbf{R}^3_\lambda$. We construct the model step-by-step and observe that physical objects known from previous studies appear in a very natural way. Nonassociativity became a topic of great interest lately, often in a connection with magnetic monopoles. We show that this model does not possess this property.




Landau Damping in a strong magnetic field: Dissociation of Quarkonia. (arXiv:1802.06874v1 [hep-ph])

We have investigated the effects of strong magnetic field on the properties of quarkonia immersed in a thermal medium of quarks and gluons and studied its quasi-free dissociation due to the Landau-damping. Thermalizing the Schwinger propagator in the lowest Landau levels for quarks and the Feynman propagator for gluons in real-time formalism, we have calculated the resummed retarded and symmetric propagators, which in turn give the real and imaginary components of dielectric permittivity, respectively. The magnetic field affects the large-distance interaction more than the short-distance interaction, as a result, the real part of potential becomes more attractive and the magnitude of imaginary part too becomes larger, compared to the thermal medium in absence of strong magnetic field. As a consequence the average size of $J/\psi$'s and $\psi^\prime$'s are increased but $\chi_c$'s get shrunk. Similarly the magnetic field affects the binding of $J/\psi$'s and $\chi_c$'s discriminately, i.e. it decreases the binding of $J/\psi$ and increases for $\chi_c$. However, the further increase in magnetic field results in the decrease of binding energies. On contrary the magnetic field increases the width of the resonances, unless the temperature is sufficiently high. We have finally studied how the presence of magnetic field affects the dissolution of quarkonia in a thermal medium due to the Landau damping, where the dissociation temperatures are found to increase compared to the thermal medium in absence of magnetic field. However, further increase of magnetic field decreases the dissociation temperatures. For example, $J/\psi$'s and $\chi_c$'s are dissociated at higher temperatures at 2 $T_c$ and 1.1 $T_c$ at a magnetic field $eB \approx 6~{\rm{and}}~4~m_\pi^2$, respectively, compared to the values 1.60 $T_c$ and 0.8 $T_c$ in the absence of magnetic field, respectively.




The double-trace spectrum of N=4 SYM at strong coupling. (arXiv:1802.06889v1 [hep-th])

The spectrum of IIB supergravity on AdS${}_5 \times S^5$ contains a number of bound states described by long double-trace multiplets in $\mathcal{N}=4$ super Yang-Mills theory at large 't Hooft coupling. At large $N$ these states are degenerate and to obtain their anomalous dimensions as expansions in $\tfrac{1}{N^2}$ one has to solve a mixing problem. We conjecture a formula for the leading anomalous dimensions of all long double-trace operators which exhibits a large residual degeneracy whose structure we describe. Our formula can be related to conformal Casimir operators which arise in the structure of leading discontinuities of supergravity loop corrections to four-point correlators of half-BPS operators.




BFKL Spectrum of N=4 SYM: non-Zero Conformal Spin. (arXiv:1802.06908v1 [hep-th])

We developed a general non-perturbative framework for the BFKL spectrum of planar $\mathcal{N}=4$ SYM, based on the Quantum Spectral Curve (QSC). It allows one to study the spectrum in the whole generality, extending previously known methods to arbitrary values of conformal spin $n$. We show how to apply our approach to reproduce all known perturbative results for the Balitsky-Fadin-Kuraev-Lipatov (BFKL) pomeron dimension and get new predictions. In particular, we re-derived the Faddeev-Korchemsky Baxter equation for the Lipatov spin chain with non-zero conformal spin reproducing the corresponding BFKL kernel eigenvalue. We also get new non-perturbative analytic results for the pomeron dimension in the vicinity of $|n|=1,\;\Delta=0$ point and we obtained an explicit formula for the BFKL intercept function for arbitrary conformal spin up to the 3-loop order in the small coupling expansion and partial result at the 4-loop order. We also implemented the numerical algorithm of arXiv:1504.06640 as an auxiliary file to this arXiv submission. From the numerical result we managed to deduce an analytic formula for the strong coupling expansion of the intercept function for arbitrary conformal spin.




Perturbative unitarity and higher-order Lorentz symmetry breaking. (arXiv:1802.06918v1 [hep-th])

We study perturbative unitarity in the scalar sector of the Myers and Pospelov model. The model introduces a preferred four vector $n$ which breaks Lorentz symmetry and couples to a five-dimension operator. When the preferred four vector is chosen in the pure timelike direction the model becomes a higher time derivative theory leading to a cubic dispersion relation. Two of the poles are shown to be perturbative connected to the standard ones, while a third pole, which we call Lee-Wick-like pole, can be associated to a negative metric, threatening the preservation of unitarity. We analyze perturbative unitarity using the optical theorem and considering a quartic self-interaction term. By computing discontinuities in the loop diagram, we arrive to a pinching condition which also determines the propagation of the Lee-Wick-like particle through the cut. We find that the contribution vanishes for real external momenta, thus preserving one-loop unitarity.




Double Field Theory and Membrane Sigma-Models. (arXiv:1802.07003v1 [hep-th])

We investigate geometric aspects of double field theory (DFT) and its formulation as a doubled membrane sigma-model. Starting from the standard Courant algebroid over the phase space of an open membrane, we determine a splitting and a projection to a subbundle that sends the Courant algebroid operations to the corresponding operations in DFT. This describes precisely how the geometric structure of DFT lies in between two Courant algebroids and is reconciled with generalized geometry. We construct the membrane sigma-model that corresponds to DFT, and demonstrate how the standard T-duality orbit of geometric and non-geometric flux backgrounds is captured by its action functional in a unified way. This also clarifies the appearence of noncommutative and nonassociative deformations of geometry in non-geometric closed string theory. Gauge invariance of the DFT membrane sigma-model is compatible with the flux formulation of DFT and its strong constraint, whose geometric origin is explained. Our approach leads to a new generalization of a Courant algebroid, that we call a DFT algebroid and relate to other known generalizations, such as pre-Courant algebroids and symplectic nearly Lie 2-algebroids. We also describe the construction of a gauge-invariant doubled membrane sigma-model that does not require imposing the strong constraint.




Hairy black hole solutions in $U(1)$ gauge-invariant scalar-vector-tensor theories. (arXiv:1802.07035v1 [gr-qc])

In $U(1)$ gauge-invariant scalar-vector-tensor theories with second-order equations of motion, we study the properties of black holes (BH) on a static and spherically symmetric background. In shift-symmetric theories invariant under the shift of scalar $\phi \to \phi+c$, we show the existence of new hairy BH solutions where a cubic-order scalar-vector interaction gives rise to a scalar hair manifesting itself around the event horizon. In the presence of a quartic-order interaction besides the cubic coupling, there are also regular BH solutions endowed with scalar and vector hairs.




Euclidean Action and the Einstein tensor. (arXiv:1802.07055v1 [gr-qc])

I give a local description of the Euclidean regime $(M, g_{ab}, u^a)$ of Lorentzian spacetimes $(M, g_{ab})$ based on timelike geodesics $u^a$ passing through an arbitrary event $p_0 \in M$. I show that, to leading order, the Euclidean Einstein-Hilbert action $I_E$ is proportional to the Einstein tensor $G_{ab}u^a u^b$ of $g_{ab}$. The positivity of $I_E$ follows if $G_{ab}u^a u^b>0$ holds. I suggest an interpretation of this result in terms of the amplitude $\mathcal{A}[\Sigma_0]=\exp[{-I_E}]$ for a single space-like hypersurface $\Sigma_0 \in I^{+}(p_0)$ to emerge at a constant geodesic distance $\lambda_0$ from $p_0$. Implications for classical and quantum gravity are discussed.




On regular frames near rotating black holes. (arXiv:1802.07069v1 [gr-qc])

We consider the metric of a generic axially symmetric rotating stationary black hole. The general approach is developed that enables us to construct coordinate frame regular near the horizon. As explicit examples, the Kerr and Kerr-Newmann-(anti-)de Sitter metrics are considered. It is shown how the rotational versions of the Painlev\'e-Gullstrand and Doran coordinates appear in this scheme as particular cases. For the 2+1 version of the metric the direct generalization of the Lema\^itre coordinate system is obtained. It is shown that the possibility of introducing a regular frame is indirectly related to the constancy of a black hole angular velocity and the rate with which the metric coefficient responsible for the rotation of spacetime, tends to it.




1/2-BPS D-branes from covariant open superstring in AdS$_4\times \mathbf{CP}^3$ background. (arXiv:1802.07070v1 [hep-th])

We consider the open superstring action in the AdS$_4 \times \mathbf{CP}^3$ background and investigate the suitable boundary conditions for the open superstring describing the 1/2-BPS D-branes by imposing the $\kappa$-symmetry of the action. This results in the classification of 1/2-BPS D-branes from covariant open superstring. It is shown that the 1/2-BPS D-brane configurations are restricted considerably by the K\"{a}hler structure on $\mathbf{CP}^3$. We just consider D-branes without worldvolume fluxes.




Symmetries near a generic charged null surface and associated algebra: an off-shell analysis. (arXiv:1802.07108v1 [gr-qc])

To understand the underlying degrees of freedom, near horizon symmetry analysis of a black has gain significant interest in the recent past. In this paper we generalized those analysis first by taking into account a generic null surface carrying $U(1)$ electromagnetic charge. With the appropriate boundary conditions near the surface under study, we identified the symmetry algebra among the subset of diffeomporphism and gauge generators which preserve the metric of the null surface and the form of the gauge field configuration. With the knowledge of those symmetries we further derived the algebra among the associated charges considering general two derivative gravity theory and gauge theory. Importantly while computing the charges we not only considered general theory, but also used off-shell formalism which is believed to play crucial role in understanding quantum gravity.




BRST-BV quantization of gauge theories with global symmetries. (arXiv:1802.07138v1 [hep-th])

We consider the general gauge theory with a closed irreducible gauge algebra possessing the non-anomalous global (super)symmetry in the case when the gauge fixing procedure violates the global invariance of classical action. The theory is quantized in the framework of BRST-BV approach in the form of functional integral over all fields of the configuration space. It is shown that the global symmetry transformations are deformed in the process of quantization and the full quantum action is invariant under such deformed global transformations in the configuration space. The deformed global transformations are calculated in an explicit form in the one-loop approximation.




Exact results for the $O(N)$ model with quenched disorder. (arXiv:1802.07151v1 [cond-mat.stat-mech])

We use scale invariant scattering theory to exactly determine the lines of renormalization group fixed points for $O(N)$-symmetric models with quenched disorder in two dimensions. Random fixed points are characterized by two disorder parameters: a modulus that vanishes when approaching the pure case, and a phase angle. The critical lines fall into three classes depending on the values of the disorder modulus. Besides the class corresponding to the pure case, a second class has maximal value of the disorder modulus and includes Nishimori-like multicritical points as well as zero temperature fixed points. The third class contains critical lines that interpolate, as $N$ varies, between the first two classes. For positive $N$, it contains a single line of infrared fixed points spanning the values of $N$ from $\sqrt{2}-1$ to $1$. The symmetry sector of the energy density operator is superuniversal (i.e. $N$-independent) along this line. For $N=2$ a line of fixed points exists only in the pure case, but accounts also for the Berezinskii-Kosterlitz-Thouless phase observed in presence of disorder.




Comment on "A structural test for the conformal invariance of the critical 3d Ising model" by S. Meneses, S. Rychkov, J. M. Viana Parente Lopes and P. Yvernay. arXiv:0802.02319. (arXiv:1802.07157v1 [hep-th])

In a recent preprint [ArXiv 0802.02319], Meneses et al. challenge our proof that scale invariance implies conformal invariance for the three-dimensional Ising model [B. Delamotte, M. Tissier and N. Wschebor, Phys. Rev. E 93 (2016), 012144.]. We refute their arguments. We also point out a mistake in their one-loop calculation of the dimension of the vector operator $V_\mu$ of lowest dimension which is not a total derivative.




Comment on the Bekenstein bound. (arXiv:1802.07184v1 [math-ph])

We propose a rigorous derivation of the Bekenstein upper limit for the entropy/information that can be contained by a physical system in a given finite region of space with given finite energy. The starting point is the observation that the derivation of such a bound provided by Casini [6] is similar to the description of the black hole incremental free energy that had been given by the first named author [23]. The approach here is different but close in the spirit to [6]. Our bound is obtained by operator algebraic methods, in particular Connes' bimodules, Tomita-Takesaki modular theory and Jones' index are essential ingredients inasmuch as the von Neumann algebras in question are typically of type III. We rely on the general mathematical framework, recently set up in [26], concerning quantum information of infinite systems.




The anisotropic \lambda-deformed SU(2) model is integrable. (arXiv:1412.5181v4 [hep-th] UPDATED)

The all-loop anisotropic Thirring model interpolates between the WZW model and the non-Abelian T-dual of the anisotropic principal chiral model. We focus on the SU(2) case and we prove that it is classically integrable by providing its Lax pair formulation. We derive its underlying symmetry current algebra and use it to show that the Poisson brackets of the spatial part of the Lax pair, assume the Maillet form. In this way we procure the corresponding r and s matrices which provide non-trivial solutions to the modified Yang-Baxter equation.




Quantum Yang-Mills Theory in Two Dimensions: Exact versus Perturbative. (arXiv:1508.06305v6 [math-ph] UPDATED)

The standard Feynman diagrammatic approach to quantum field theories assumes that perturbation theory approximates the full quantum theory at small coupling even when a mathematically rigorous construction of the latter is absent. On the other hand, two-dimensional Yang-Mills theory is a rare (if not the only) example of a nonabelian (pure) gauge theory whose full quantum theory has a rigorous construction. Indeed, the theory can be formulated via a lattice approximation, from which Wilson loop expecation values in the continuum limit can be described in terms of heat kernels on the gauge group. It is therefore fundamental to investigate how the exact answer for 2D Yang-Mills compares with that of the continuum perturbative approach, which a priori are unrelated. In this paper, we provide a mathematically rigorous formulation of the perturbative quantization of 2D Yang-Mills, and we consider perturbative Wilson loop expectation values on $\mathbb{R}^2$ and $S^2$ in Coulomb gauge, holomorphic gauge, and axial gauge (on $\mathbb{R}^2$). We show the following equivalences and nonequivalences between these gauges: (i) Coulomb and holomorphic gauge are equivalent and are independent of the choice of gauge-fixing metric; (ii) both are inequivalent with axial-gauge. Additionally, we show that the asymptotics of exact lattice Wilson loop expectations on $S^2$ agree with perturbatively computed expectations in holomorphic gauge for simple closed curves to all orders. However, as a consequence of (ii), this result is necessarily false on $\mathbb{R}^2$. Our work therefore presents fundamental progress in the analysis of how continuum perturbation theory succeeds or fails in capturing the asymptotics of the continuum limit of the lattice theory.




Stochastic Feynman Rules for Yang-Mills Theory on the Plane. (arXiv:1607.07463v3 [math-ph] UPDATED)

We analyze quantum Yang-Mills theory on $\mathbb{R}^2$ using a novel discretization method based on an algebraic analogue of stochastic calculus. Such an analogue involves working with "Gaussian" free fields whose covariance matrix is indefinite rather than positive definite. Specifically, we work with Lie-algebra valued fields on a lattice and exploit an approximate gauge-invariance that is restored when taking the continuum limit. This analysis is applied to show the equivalence between Wilson loop expectations computed using partial axial-gauge, complete axial-gauge, and the Migdal-Witten lattice formulation. As a consequence, we obtain intriguing Lie-theoretic identities involving heat kernels and iterated integrals.




Four dimensional ambitwistor strings and form factors of local and Wilson line operators. (arXiv:1704.04758v4 [hep-th] UPDATED)

We consider the description of form factors of local and Wilson line operators (reggeon amplitudes) in N=4 SYM within the framework of four dimensional ambitwistor string theory. We present the explicit expressions for string composite operators corresponding to stress-tensor operator supermultiplet and Wilson line operator insertion. It is shown, that corresponding tree-level string correlation functions correctly reproduce previously obtained Grassmannian integral representations. As by product we derive four dimensional tree-level scattering equations representations for the mentioned form factors and formulate a simple gluing procedure used to relate operator form factors with on-shell amplitudes.




Monopole-antimonopole Interaction Potential. (arXiv:1705.03091v3 [hep-th] UPDATED)

We numerically study the interactions of twisted monopole-antimonopole pairs in the 't Hooft-Polyakov model for a range of values of the scalar to vector mass ratio. We also recover the sphaleron solution at maximum twist discovered by Taubes, and map out its energy and size as functions of parameters.




Dynamics of Relaxed Inflation. (arXiv:1706.03072v2 [hep-ph] UPDATED)

The cosmological relaxation of the electroweak scale has been proposed as a mechanism to address the hierarchy problem of the Standard Model. A field, the relaxion, rolls down its potential and, in doing so, scans the squared mass parameter of the Higgs, relaxing it to a parametrically small value. In this work, we promote the relaxion to an inflaton. We couple it to Abelian gauge bosons, thereby introducing the necessary dissipation mechanism which slows down the field in the last stages. We describe a novel reheating mechanism, which relies on the gauge-boson production leading to strong electromagnetic fields, and proceeds via the vacuum production of electron-positron pairs through the Schwinger effect. We refer to this mechanism as Schwinger reheating. We discuss the cosmological dynamics of the model and the phenomenological constraints from CMB and other experiments. We find that a cutoff close to the Planck scale may be achieved. In its minimal form, the model does not generate sufficient curvature perturbations and additional ingredients, such as a curvaton field, are needed.




$q$-Poincar\'e supersymmetry in $AdS_5/CFT_4$. (arXiv:1706.10265v2 [hep-th] UPDATED)

We consider the exact S-matrix governing the planar spectral problem for strings on $AdS_5\times S^5$ and $\mathcal N=4$ super Yang-Mills, and we show that it is invariant under a novel "boost" symmetry, which acts as a differentiation with respect to the particle momentum. This generator leads us also to reinterpret the usual centrally extended $\mathfrak{psu}(2|2)$ symmetry, and to conclude that the S-matrix is invariant under a $q$-Poincar\'e supersymmetry algebra, where the deformation parameter is related to the 't Hooft coupling. We determine the two-particle action (coproduct) that turns out to be non-local, and study the property of the new symmetry under crossing transformations. We look at both the strong-coupling (large tension in the string theory) and weak-coupling (spin-chain description of the gauge theory) limits; in the former regime we calculate the cobracket utilising the universal classical r-matrix of Beisert and Spill. In the eventuality that the boost has higher partners, we also construct a quantum affine version of 2D Poincar\'e symmetry, by contraction of the quantum affine algebra $U_q(\widehat{\mathfrak{sl}_2})$ in Drinfeld's second realisation.




Gauss-Bonnet for matrix conformally rescaled Dirac. (arXiv:1707.04438v2 [math.QA] UPDATED)

We derive an explicit formula for the scalar curvature over a two-torus with a Dirac operator conformally rescaled by a globally diagonalizable matrix. We show that the Gauss-Bonnet theorem holds and extend the result to all Riemann surfaces with Dirac operators modified in the same way.




Gravitons emission during pre-inflation from unified spinor fields. (arXiv:1709.01162v3 [gr-qc] UPDATED)

We obtain the equation that describe the conditions of quantization for neutral massless bosons on an arbitrary curved space-time, obtained using a particular theoretical formalism developed in a previous work\cite{MM}. In particular, we study the emission of neutral massless $(1, 2)\hbar$-spin bosons during pre-inflation using the recently introduced unified spinor field theory. We conclude that during pre-inflation (which is governed by an vacuum equation of state), is emitted gravitational radiation, which could be detected in the future, as primordial gravitational radiation.




Setting Initial Conditions for Inflation with Reaction-Diffusion Equation. (arXiv:1709.02678v4 [hep-th] UPDATED)

We discuss the issue of setting appropriate initial conditions for inflation. Specifically, we consider natural inflation model and discuss the fine tuning required for setting almost homogeneous initial conditions over a region of order several times the Hubble size which is orders of magnitude larger than any relevant correlation length for field fluctuations. We then propose to use the special propagating front solutions of reaction-diffusion equations for localized field domains of smaller sizes. Due to very small velocities of these propagating fronts we find that the inflaton field in such a ${\it field domain}$ changes very slowly, contrary to naive expectation of rapid roll down to the true vacuum. Continued expansion leads to the energy density in the Hubble region being dominated by the vacuum energy, thereby beginning the inflationary phase. Our results show that inflation can occur even with a single localized field domain of size smaller than the Hubble size. We discuss possible extensions of our results for different inflationary models, as well as various limitations of our analysis (e.g. neglecting self gravity of the localized field domain).




Neutron star mergers as a probe of modifications of general relativity with finite-range scalar forces. (arXiv:1709.06634v3 [gr-qc] UPDATED)

Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test General Relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universally coupled massive scalar field. Such scalar degrees of freedom are a characteristic feature of many extensions of General Relativity. For concreteness, we work in the context of metric $f(R)$ gravity, which is equivalent to General Relativity and a universally coupled scalar field with a non-linear potential whose form is fixed by the choice of $f(R)$. In theories where neutron stars (or other compact objects) obtain a significant scalar charge, the resulting attractive finite-range scalar force has implications for both the inspiral and merger phases of binary systems. We first present an analysis of the inspiral dynamics in Newtonian limit, and forecast the constraints on the mass of the scalar and charge of the compact objects for the Advanced LIGO gravitational wave observatory. We then perform a comparative study of binary neutron star mergers in General Relativity with those of a one-parameter model of $f(R)$ gravity using fully relativistic hydrodynamical simulations. These simulations elucidate the effects of the scalar on the merger and post-merger dynamics. We comment on the utility of the full waveform (inspiral, merger, post-merger) to probe different regions of parameter space for both the particular model of $f(R)$ gravity studied here and for finite-range scalar forces more generally.




Manyfield Inflation in Random Potentials. (arXiv:1709.10076v2 [astro-ph.CO] UPDATED)

We construct models of inflation with many randomly interacting fields and use these to study the generation of cosmological observables. We model the potentials as multi-dimensional Gaussian random fields (GRFs) and identify powerful algebraic simplifications that, for the first time, make it possible to access the manyfield limit of inflation in GRF potentials. Focussing on small-field, slow-roll, approximate saddle-point inflation in potentials with structure on sub-Planckian scales, we construct explicit examples involving up to 100 fields and generate statistical ensembles comprising of 164,000 models involving 5 to 50 fields. For the subset of these that support at least sixty e-folds of inflation, we use the 'transport method' and $\delta N$ formalism to determine the predictions for cosmological observables at the end of inflation, including the power spectrum and the local non-Gaussianities of the primordial perturbations. We find three key results: i) Planck compatibility is not rare, but future experiments may rule out this class of models; ii) In the manyfield limit, the predictions from these models agree well with, but are sharper than, previous results derived using potentials constructed through non-equilibrium Random Matrix Theory; iii) Despite substantial multifield effects, non-Gaussianities are typically very small: $f_{\rm nl}^{\rm loc} \ll 1$. We conclude that many of the 'generic predictions' of single-field inflation can be emergent features of complex inflation models.




Non-equilibrium evolution of quantum fields during inflation and late accelerating expansion. (arXiv:1711.01925v2 [gr-qc] UPDATED)

We consider a toy model including 3 scalar fields with different masses to study the formation of a light axion-like condensate presumed to be responsible for inflation and/or late accelerating expansion of the Universe. The investigation is performed in the framework of non-equilibrium quantum field theory in a consistently evolved FLRW geometry. We discuss in details how the initial conditions for such a model must be defined in a fully quantum setup and show that in a multi-component model coupling between fields highly reduce the number of independent initial degrees of freedom. Numerical simulation of this model shows that it can be fully consistent with present cosmological observations. For the chosen range of parameters we find that quantum interactions rather than effective potential of a condensate is the dominate contributor in the energy density of the Universe and triggers both inflation and late accelerating expansion. Nonetheless, despite its small contribution in the energy density, the light scalar field, in both condensate and perturbatively free particle forms, has a crucial role in controlling the trend of heavier fields. Furthermore, up to precision of our simulations we do not find any IR singularity during inflation. These findings highlight uncertainties in attempts to extract information about physics of early Universe by naively comparing predictions of local effective classical models with cosmological observations, neglecting inherently non-local nature of quantum processes.




Non-Abelian $S$-term dark energy and inflation. (arXiv:1711.01935v4 [gr-qc] UPDATED)

We study the role that a cosmic triad in the generalized $SU(2)$ Proca theory, specifically in one of the pieces of the Lagrangian that involves the symmetric version $S_{\mu \nu}$ of the gauge field strength tensor $F_{\mu \nu}$, has on dark energy and primordial inflation. Regarding dark energy, the triad behaves asymptotically as a couple of radiation perfect fluids whose energy densities are negative for the $S$ term but positive for the Yang-Mills term. This leads to an interesting dynamical fine-tuning mechanism that gives rise to a combined equation of state parameter $\omega \simeq -1$ and, therefore, to an eternal period of accelerated isotropic expansion for an ample spectrum of initial conditions. Regarding primordial inflation, one of the critical points of the associated dynamical system can describe a prolonged period of isotropic slow-roll inflation sustained by the $S$ term. This period ends up when the Yang-Mills term dominates the energy density leading to the radiation dominated epoch. Unfortunately, in contrast to the dark energy case, the primordial inflation scenario is strongly sensitive to the coupling constants and initial conditions. The whole model, including the other pieces of the Lagrangian that involve $S_{\mu \nu}$, might evade the recent strong constraints coming from the gravitational wave signal GW170817 and its electromagnetic counterpart GRB 170817A.




Nonunitary Lagrangians and unitary non-Lagrangian conformal field theories. (arXiv:1711.09949v2 [hep-th] UPDATED)

In various dimensions, we can sometimes compute observables of interacting conformal field theories (CFTs) that are connected to free theories via the renormalization group (RG) flow by computing protected quantities in the free theories. On the other hand, in two dimensions, it is often possible to algebraically construct observables of interacting CFTs using free fields without the need to explicitly construct an underlying RG flow. In this note, we begin to extend this idea to higher dimensions by showing that one can compute certain observables of an infinite set of unitary strongly interacting four-dimensional $\mathcal{N}=2$ superconformal field theories (SCFTs) by performing simple calculations involving sets of non-unitary free four-dimensional hypermultiplets. These free fields are distant cousins of the Majorana fermion underlying the two-dimensional Ising model and are not obviously connected to our interacting theories via an RG flow. Rather surprisingly, this construction gives us Lagrangians for particular observables in certain subsectors of many "non-Lagrangian" SCFTs by sacrificing unitarity while preserving the full $\mathcal{N}=2$ superconformal algebra. As a byproduct, we find relations between characters in unitary and non-unitary affine Kac-Moody algebras. We conclude by commenting on possible generalizations of our construction.




Canonical transformation path to gauge theories of gravity II --- Spacetime coupling of massive spin particle fields. (arXiv:1711.10333v2 [gr-qc] UPDATED)

The generic form of spacetime dynamics as a gauge theory has recently been derived, based on only the action principle and on the general principle of relativity. In the present paper, the physical consequences are discussed. The gauge coupling terms obtained imply that Einstein's theory holds only for structureless (spin zero) particles, and aggregations of them. For massive particles with spin, however, spacetime dynamics is to be described by an additional, Poisson-type equation describing the interaction of the particle's spin with the torsion of spacetime. This equation shows that torsion propagates with gravitational waves. Spin carrying matter is thus shown to couple with the torsion of spacetime. The proper source term for the spacetime dynamics is given by the canonical energy-momentum tensor---which embraces also the energy density furnished by microscopic internal spin. This changes the model of compact astrophysical objects and of relativistic collapse dynamics, with significant impact on the description of binary neutron star mergers and pulsar dynamics. The final generally covariant Hamiltonian must contain a term quadratic in the conjugate momenta of the gauge fields in order to yield a closed system of field equations---in analogy to all other Hamiltonian descriptions of field theories. The fact that the canonical gauge theory of gravity derived here requires that both, quadratic curvature tensors and canonical energy momentum tensors, enter the field equation for the spacetime dynamics leads to a qualitatively new framework for general relativity---and to a new understanding of Friedman cosmology and the cosmological constant problem.




Towards an M5-Brane Model I: A 6d Superconformal Field Theory. (arXiv:1712.06623v2 [hep-th] UPDATED)

We present an action for a six-dimensional superconformal field theory containing a non-abelian tensor multiplet. All of the ingredients of this action have been available in the literature. We bring these pieces together by choosing the string Lie 2-algebra as a gauge structure, which we motivated in previous work. The kinematical data contains a connection on a categorified principal bundle, which is the appropriate mathematical description of the parallel transport of self-dual strings. Our action can be written down for each of the simply laced Dynkin diagrams, and each case reduces to a four-dimensional supersymmetric Yang--Mills theory with corresponding gauge Lie algebra. Our action also reduces nicely to an M2-brane model which is a deformation of the ABJM model. While this action is certainly not the desired M5-brane model, we regard it as a key stepping stone towards a potential construction of the (2,0)-theory.




Nilpotent ${\cal N}=1$ tensor multiplet. (arXiv:1712.09258v2 [hep-th] UPDATED)

We propose a nilpotent ${\cal N}=1$ tensor multiplet describing two fields, which are the Goldstino and the axion, the latter being realised in terms of the field strength of a gauge two-form. This supersymmetric multiplet is formulated in terms of a deformed real linear superfield, subject to a cubic nilpotency condition. Its couplings to a super Yang-Mills multiplet and supergravity are presented. To define a nilpotent tensor multiplet in the locally supersymmetric case, one has to make use of either real or complex three-form supergravity theories, which are variant realisations of the old minimal formulation for ${\cal N}=1$ supergravity.




Holographic Complexity of Einstein-Maxwell-Dilaton Gravity. (arXiv:1712.09826v2 [hep-th] UPDATED)

We study the holographic complexity of Einstein-Maxwell-Dilaton gravity using the recently proposed "complexity = volume" and "complexity = action" dualities. The model we consider has a ground state that is represented in the bulk via a so-called hyperscaling violating geometry. We calculate the action growth of the Wheeler-DeWitt patch of the corresponding black hole solution at non-zero temperature and find that, in the presence of violations of hyperscaling, there is a parametric enhancement of the action growth rate. We partially match this behavior to simple tensor network models which can capture aspects of hyperscaling violation. We also exhibit the switchback effect in complexity growth using shockwave geometries and comment on a subtlety of our action calculations when the metric is discontinuous at a null surface.




Laughlin states on higher genus Riemann surfaces. (arXiv:1712.09980v2 [cond-mat.str-el] UPDATED)

Considering quantum Hall states on geometric backgrounds has proved over the past few years to be a useful tool for uncovering their less evident properties, such as gravitational and electromagnetic responses, topological phases and novel geometric adiabatic transport coefficients. One of the transport coefficients, the central charge associated with the gravitational anomaly, appears as a Chern number for the adiabatic transport on the moduli spaces of higher genus Riemann surfaces. This calls for a better understanding of the QH states on these backgrounds. Here we give a detailed account of the construction of Laughlin states on Riemann surfaces of genus ${\rm g}>1$. We present a rigorous definition of the Laughlin states and their explicit construction, based on the path integral for the 2d bosonic field compactified on a circle, reproducing the conjectured $\beta^{\rm g}$-fold degeneracy for the filling fraction $\nu=1/\beta$. We also discuss the lowest Landau level, integer QH state and its relation to the bosonization formulas on higher genus Riemann surfaces.




Beyond dRGT as Mimetic Massive. (arXiv:1801.07958v3 [gr-qc] UPDATED)

An interesting proposal has recently been made to extend massive gravity models beyond dRGT by a disformal transformation of the metric. In this Letter we want to note that it can be viewed as a mimetic extension of dRGT gravity which enormously simplifies the Hamiltonian analysis. In particular, pure gravity sector is equivalent to the usual dRGT gravity coupled to a constrained scalar field. And we also give some comments about possible matter couplings.




KLT-type relations for QCD and bicolor amplitudes from color-factor symmetry. (arXiv:1802.01620v2 [hep-th] UPDATED)

Color-factor symmetry is used to derive a KLT-type relation for tree-level QCD amplitudes containing gluons and an arbitrary number of massive or massless quark-antiquark pairs, generalizing the expression for Yang-Mills amplitudes originally postulated by Bern, De Freitas, and Wong. An explicit expression is given for all amplitudes with two or fewer quark-antiquark pairs in terms of the (modified) momentum kernel.

We also introduce the bicolor scalar theory, the "zeroth copy" of QCD, containing massless biadjoint scalars and massive bifundamental scalars, generalizing the biadjoint scalar theory of Cachazo, He, and Yuan. We derive KLT-type relations for tree-level amplitudes of biadjoint and bicolor theories using the color-factor symmetry possessed by these theories.




LeClair-Mussardo series for two-point functions in Integrable QFT. (arXiv:1802.05890v2 [hep-th] UPDATED)

We develop a well-defined spectral representation for two-point functions in relativistic Integrable QFT in finite density situations, valid for space-like separations. The resulting integral series is based on the infinite volume, zero density form factors of the theory, and certain statistical functions related to the distribution of Bethe roots in the finite density background. Our final formulas are checked by comparing them to previous partial results obtained in a low-temperature expansion. It is also show that in the limit of large separations the new integral series factorizes into the product of two LeClair-Mussardo series for one-point functions, thereby satisfying the clustering requirement for the two-point function.




Boson-fermion duality in three dimensions. (arXiv:1802.06087v2 [cond-mat.str-el] UPDATED)

We study the 2+1 dimensional boson-fermion duality in the presence of background curvature and electromagnetic fields. The main players are, on the one hand, free massive complex scalar fields coupled to U(1) Maxwell-Chern-Simons gauge fields at Chern-Simons levels $\pm1$, representing relativistic composite bosons with one unit of attached flux, and on the other hand, free massive Dirac fermions. We prove, in a curved background and at the level of the partition function, that a doublet of relativistic composite bosons, in the infinite coupling limit, is dual to a doublet of Dirac fermions. The spin connection arises from the expectation value of the Wilson loop in the Chern-Simons theory, whereas a non-minimal coupling of bosons to the scalar curvature is necessary in order to obtain agreement between partition functions. Remarkably, we find that the correspondence does not hold in the presence of background electromagnetic fields, a pathology rooted to the coupling of electromagnetism to the spin angular momentum of the Dirac spinor, which can not be reproduced from minimal coupling in the bosonic side. The presence of framing and parity anomalies in the Chern-Simons and fermionic theories, respectively, poses a difficulty in realizing the duality as an exact mapping between partition functions. The existence of non matching anomalies is circumvented by the Dirac fermions coming in pairs, making the fermionic theory parity anomaly free, and by the inclusion of a Maxwell term in the bosonic side, acting as a regulator forcing the CS theory to be quantized in a non-topological way. The Coulomb interaction stemming from the Maxwell term is also of key importance to prevent intersections of worldlines in the path integral. An extension of the duality to the massless case fails if bosons and fermions are in a topological phase, but is possible when the mapping is between trivial theories.




The quest for Casimir repulsion between Chern-Simons surfaces. (arXiv:1802.06598v1 [cond-mat.mes-hall] CROSS LISTED)

In this paper we critically reconsider the Casimir repulsion between surfaces that carry the Chern-Simons interaction (corresponding to the Hall type conductivity). We present a derivation of the Lifshitz formula valid for arbitrary planar geometries and discuss its properties. This analysis allows us to resolve some contradictions in the previous literature. We compute the Casimir energy for two surfaces that have constant longitudinal and Hall conductivities. The repulsion is possible only if both surfaces have Hall conductivities of the same sign. However, there is a critical value of the longitudinal conductivity above which the repulsion disappears. We also consider a model where both parity odd and parity even terms in the conductivity are produced by the polarization tensor of surface modes. In contrast to the previous publications L. Chen and S.-L. Wan, Phys. Rev. B84, 075149 (2011); B85, 115102 (2012), we include the parity anomaly term. This term ensures that the conductivities vanish for infinitely massive surface modes. We find that at least for a single mode regardless of the sign and value of its mass, there is no Casimir repulsion.