Publications

2020

• Hints of unitarity at large $N$ in the $O(N)^3$ tensor field theory
  
  • Benedetti Dario
  • Gurau Razvan
  • Harribey Sabine
  • Suzuki Kenta
  Journal of High Energy Physics, Springer, 2020, 2020 (2), pp.72. We compute the OPE coefficients of the bosonic tensor model of \cite{Benedetti:2019eyl} for three point functions with two fields and a bilinear with zero and non-zero spin. We find that all the OPE coefficients are real in the case of an imaginary tetrahedral coupling constant, while one of them is not real in the case of a real coupling. We also discuss the operator spectrum of the free theory based on the character decomposition of the partition function. (10.1007/JHEP02(2020)072)
  DOI : 10.1007/JHEP02(2020)072
• Probing spin correlations using angle-resolved photoemission in a coupled metallic/Mott insulator system
  
  • Sunko Veronika
  • Mazzola Federico
  • Kitamura Sota
  • Khim Seunghyun
  • Kushwaha Pallavi
  • Clark Oliver J
  • Watson Matthew D
  • Marković Igor
  • Biswas Deepnarayan
  • Pourovskii Leonid
  • Kim Timur
  • Lee Tien-Lin
  • Thakur Pardeep Kumar
  • Rosner Helge
  • Georges Antoine
  • Moessner Roderich
  • Oka Takashi
  • Mackenzie Andrew
  • King Philip
  Science Advances, American Association for the Advancement of Science (AAAS), 2020, 6 (6), pp.eaaz0611. A nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO2, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an “intertwined” excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO2 as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials. (10.1126/sciadv.aaz0611)
  DOI : 10.1126/sciadv.aaz0611
• Finite-temperature density matrix embedding theory
  
  • Sun Chong
  • Ray Ushnish
  • Cui Zhi-Hao
  • Stoudenmire Miles
  • Ferrero M.
  • Chan Garnet Kin-Lic
  Physical Review B, American Physical Society, 2020, 101 (7), pp.075131. We describe a formulation of the density matrix embedding theory at finite temperature. We present a generalization of the ground-state bath orbital construction that embeds a mean-field finite-temperature density matrix up to a given order in the Hamiltonian, or the Hamiltonian up to a given order in the density matrix. We assess the performance of the finite-temperature density matrix embedding on the one-dimensional Hubbard model both at half-filling and away from it, and the two-dimensional Hubbard model at half-filling, comparing to exact data where available, as well as results from finite-temperature density matrix renormalization group, dynamical mean-field theory, and dynamical cluster approximations. The accuracy of finite-temperature density matrix embedding appears comparable to that of the ground-state theory, with, at most, a modest increase in bath size, and competitive with that of cluster dynamical mean-field theory. (10.1103/PhysRevB.101.075131)
  DOI : 10.1103/PhysRevB.101.075131
• Real-frequency diagrammatic Monte Carlo at finite temperature
  
  • Vučičević J.
  • Ferrero M.
  Physical Review B, American Physical Society, 2020, 101 (7), pp.075113. Diagrammatic expansions are a central tool for treating correlated electron systems. At thermal equilibrium, they are most naturally defined within the Matsubara formalism. However, extracting any dynamic response function from a Matsubara calculation ultimately requires the ill-defined analytical continuation from the imaginary- to the real-frequency domain. It was recently proposed [Phys. Rev. B 99, 035120 (2019)] that the internal Matsubara summations of any interaction-expansion diagram can be performed analytically by using symbolic algebra algorithms. The result of the summations is then an analytical function of the complex frequency rather than Matsubara frequency. Here we apply this principle and develop a diagrammatic Monte Carlo technique which yields results directly on the real-frequency axis. We present results for the self-energy Σ(ω) of the doped 32x32 cyclic square-lattice Hubbard model in a non-trivial parameter regime, where signatures of the pseudogap appear close to the antinode. We discuss the behavior of the perturbation series on the real-frequency axis and in particular show that one must be very careful when using the maximum entropy method on truncated perturbation series. Our approach holds great promise for future application in cases when analytical continuation is difficult and moderate-order perturbation theory may be sufficient to converge the result. (10.1103/PhysRevB.101.075113)
  DOI : 10.1103/PhysRevB.101.075113
• Data-driven study of timelike Compton scattering
  
  • Grocholski O.
  • Moutarde H.
  • Pire B.
  • Sznajder P.
  • Wagner J.
  European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2020, 80, pp.171. In the framework of collinear QCD factorization, the leading twist scattering amplitudes for deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) are intimately related thanks to analytic properties of leading and next-to-leading order amplitudes. We exploit this welcome feature to make data-driven predictions for TCS observables to be measured in near future experiments. Using a recent extraction of DVCS Compton form factors from most of the existing experimental data for that process, we derive TCS amplitudes and calculate TCS observables only assuming leading-twist dominance. Artificial neural network techniques are used for an essential reduction of model dependency, while a careful propagation of experimental uncertainties is achieved with replica methods. Our analysis allows for stringent tests of the leading twist dominance of DVCS and TCS amplitudes. Moreover, this study helps to understand quantitatively the complementarity of DVCS and TCS measurements to test the universality of generalized parton distributions, which is crucial e.g. to perform the nucleon tomography. (10.1140/epjc/s10052-020-7700-9)
  DOI : 10.1140/epjc/s10052-020-7700-9
• Mean field flow equations and asymptotically free scalar fields
  
  • Kopper Christoph
  , 2020. The flow equations of the renormalisation group permit to analyse the perturbative $n$-point functions of renormalisable quantum field theories. Rigorous bounds implying renormalisablility allow to control large momentum behaviour, infrared singularities and large order behaviour in the number of loops and the number of arguments $n\,$. Gauge symmetry which is broken by the flow in momentum or position space, can be shown to be restored in the renormalised theory. In this paper we want to do a first but important step towards a rigorous nonperturbative analysis of the flow equations (FEs). We restrict to massive scalar fields and analyse the {\it mean field limit} where the Schwinger or 1PI functions are considered to be momentum independent or, otherwise stated, are replaced by their zero momentum values. We regard smooth solutions of the system of FEs for the $n$-point functions for different sets of boundary conditions. We will realise that allowing for non\-vanishing irrelevant terms permits to construct {\it asymptotically free} and thus nontrivial {\it scalar field theories} in the mean field approximation. We will also analyse the so-called trivial solution so far generally believed to exhaust four-dimensional scalar field theory. The method paves the way to a study of the system of FEs beyond the mean field limit.
• Dark-Matter Spontaneous Freeze Out
  
  • Partouche Hervé
  , 2020. We consider the possibility that thermalized dark-matter particles acquire their mass thanks to the spontaneous breaking of a symmetry below some critical temperature. We describe the regime where a freeze out mechanism takes place shortly after the onset of the phase transition, while the dark-matter mass has not yet reached its final constant value. For such a “spontaneous freeze out” to yield the correct relic density, the present-time cross section of annihilation of the dark matter into Standard-Model states has to be one or two orders of magnitude larger than in the case of a constant dark-matter mass.
• Comparison of improved TMD and CGC frameworks in forward quark dijet production
  
  • Fujii Hirotsugu
  • Marquet Cyrille
  • Watanabe Kazuhiro
  Journal of High Energy Physics, Springer, 2020, 12, pp.181. For studying small-x gluon saturation in forward dijet production in high-energy dilute-dense collisions, the improved TMD (ITMD) factorization formula was recently proposed. In the Color Glass Condensate (CGC) framework, it represents the leading term of an expansion in inverse powers of the hard scale. It contains the leading-twist TMD factorization formula relevant for small gluon’s transverse momentum k$_{t}$, but also incorporates an all-order resummation of kinematical twists, resulting in a proper matching to high-energy factorization at large k$_{t}$. In this paper, we evaluate the accuracy of the ITMD formula quantitatively, for the case of quark dijet production in high-energy proton-proton(p+p) and proton-nucleus (p+A) collisions at LHC energies. We do so by comparing the quark-antiquark azimuthal angle ∆ϕ distribution to that obtained with the CGC formula. For a dijet with each quark momentum p$_{t}$ much larger than the target saturation scale, Q$_{s}$, the ITMD formula is a good approximation to the CGC formula in a wide range of azimuthal angle. It becomes less accurate as the jet p$_{t}$’s are lowered, as expected, due to the presence of genuine higher-twists contributions in the CGC framework, which represent multi-body scattering effects absent in the ITMD formula. We find that, as the hard jet momenta are lowered, the accuracy of ITMD start by deteriorating at small angles, in the high-energy-factorization regime, while in the TMD regime near ∆ϕ = π, very low values of p$_{t}$ are needed to see differences between the CGC and the ITMD formula. In addition, the genuine twists corrections to ITMD become visible for higher values of p$_{t}$ in p + A collisions, compared to p+p collisions, signaling that they are enhanced by the target saturation scale. (10.1007/JHEP12(2020)181)
  DOI : 10.1007/JHEP12(2020)181
• How to generate the tip of branching random walks evolved to large times
  
  • Brunet Éric
  • Le Anh Dung
  • Mueller Alfred H.
  • Munier Stéphane
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2020, 131 (4), pp.40002. In a branching process, the number of particles increases exponentially with time, which makes numerical simulations for large times difficult. In many applications, however, only the region close to the extremal particles is relevant (the "tip"). We present a simple algorithm which allows to simulate a branching random walk in one dimension, keeping only the particles that arrive within some distance of the rightmost particle at a predefined time $T$. The complexity of the algorithm grows linearly with $T$. We can furthermore choose to require that the realizations have their rightmost particle arbitrarily far on the right from its typical position. We illustrate our algorithm by evaluating an observable for which no other practical method is known. (10.1209/0295-5075/131/40002)
  DOI : 10.1209/0295-5075/131/40002
• Deconfined critical point in a doped random quantum Heisenberg magnet
  
  • Joshi Darshan G.
  • Li Chenyuan
  • Tarnopolsky Grigory
  • Georges Antoine
  • Sachdev Subir
  Physical Review X, American Physical Society, 2020, 10 (2), pp.021033. We describe the phase diagram of electrons on a fully connected lattice with random hopping, subject to a random Heisenberg spin exchange interaction between any pair of sites and a constraint of no double occupancy. A perturbative renormalization group analysis yields a critical point with fractionalized excitations at a nonzero critical value pc of the hole doping p away from the half-filled insulator. We compute the renormalization group to two loops, but some exponents are obtained to all loop order. We argue that the critical point pc is flanked by confining phases: a disordered Fermi liquid with carrier density 1+p for p>pc and a metallic spin glass with carrier density p for p<pc. Additional evidence for the critical behavior is obtained from a large-M analysis of a model which extends the SU(2) spin symmetry to SU(M). We discuss the relationship of the vicinity of this deconfined quantum critical point to key aspects of cuprate phenomenology. (10.1103/PhysRevX.10.021033)
  DOI : 10.1103/PhysRevX.10.021033
• Probing parton saturation with forward $Z^0$-boson production at small transverse momentum in p+p and p+A collisions
  
  • Marquet Cyrille
  • Wei Shu-Yi
  • Xiao Bo-Wen
  Physics Letters B, Elsevier, 2020, 802, pp.135253. We calculate and compare the differential cross sections for forward Z0 -boson production at small transverse momentum, in proton-proton and proton-nucleus collisions, using both the collinear and dilute-dense factorization frameworks. In both cases, we implement a Sudakov resummation of the large logarithms generated by soft-gluon emissions, which is essential in order to describe the transverse momentum distribution of forward Z0 bosons measured at the Tevatron and the LHC. We further compute the nuclear modification factor in the dilute-dense framework, hoping to single out signals of saturation effects at small values of x . Our predictions are compared with those obtained in the collinear factorization framework, using two different nuclear parton distribution functions. (10.1016/j.physletb.2020.135253)
  DOI : 10.1016/j.physletb.2020.135253
• Transition Distribution Amplitudes : from JLab to EIC
  
  • Szymanowski L.
  • Pire B.
  • Semenov-Tian-Shansky K.
  , 2020, pp.16-19. Baryon-to-meson Transition Distribution Amplitudes extend both the concepts of generalized parton distributions and baryon distribution amplitudes encoding valuable complementary information on the 3-dimensional hadronic structure. The recent analysis of backward meson electroproduction at JLab supports the hope to perform femto-photography of hadrons from a brand new perspective.and in particular opens a new domain for EIC experiments.
• The ghost-antighost-gluon vertex from the Curci-Ferrari model: Two-loop corrections
  
  • Barrios Nahuel
  • Peláez Marcela
  • Reinosa Urko
  • Wschebor Nicolás
  Physical Review D, American Physical Society, 2020, 102, pp.114016. The Curci-Ferrari model has been shown to provide a good grasp on pure Yang-Mills correlation functions in the Landau gauge, already at one-loop order. In a recent work, the robustness of these results has been tested by evaluating the two-loop corrections to the gluon and ghost propagators. We pursue this systematic investigation by computing the ghost-antighost-gluon vertex to the same accuracy in a particular kinematic configuration that makes the calculations simpler. Because both the parameters of the model and the normalizations of the fields have already been fixed in a previous work, the present calculation represents both a pure prediction and a stringent test of the approach. We find that the two-loop results systematically improve the comparison to Monte-Carlo simulations as compared to earlier one-loop results. The improvement is particularly significative in the SU($3$) case where the predicted ghost-antighost-gluon vertex is in very good agreement with the data. The same comparison in the SU($2$) case is not as good, however. This may be due to the presence of a larger coupling constant in the infrared in that case although we note that a similar mismatch has been quoted in non-perturbative continuum approaches. Despite these features of the SU($2$) case, it is possible to find sets of parameters fitting both the propagators and the ghost-antighost-gluon vertex to a reasonable accuracy. (10.1103/PhysRevD.102.114016)
  DOI : 10.1103/PhysRevD.102.114016
• Valence bond fluctuations in the Kitaev spin model
  
  • Yang Fan
  • Plekhanov Kirill
  • Le Hur Karyn
  Physical Review Research, American Physical Society, 2020, 2 (1), pp.013005. We introduce valence bond fluctuations, or bipartite fluctuations associated to bond-bond correlation functions, to characterize quantum spin liquids and the entanglement properties of them. Using analytical and numerical approaches, we find an identical scaling law between valence bond fluctuations and entanglement entropy in the two-dimensional Kitaev spin model and in one-dimensional chain analogs. We also show how these valence bond fluctuations can locate, via the linear scaling prefactor, the quantum phase transitions between the three gapped and the gapless Majorana semimetal phases in the honeycomb model. We then study the effect of a uniform magnetic field along the [111] direction opening a gap in the intermediate phase which becomes topological. We still obtain a robust signal to characterize the transitions toward the three gapped phases. The area-law behavior of such bipartite fluctuations in two dimensions is also distinguishable from the one in the Néel magnetic state that follows a volume square growth. (10.1103/PhysRevResearch.2.013005)
  DOI : 10.1103/PhysRevResearch.2.013005
• Constructing Field Theories Using Quantum Simulators
  
  • Sanchez-Palencia Laurent
  Physics Magazine, American Physical Society [2008-....], 2020, 13, pp.10. Quantum simulators can help researchers extract the key parameters of a quantum field theory from experiments. (10.1103/Physics.13.10)
  DOI : 10.1103/Physics.13.10
• Super-statistical description of thermo-magnetic properties of a system of 2D GaAs quantum dots with gaussian confinement and Rashba spin–orbit interaction
  
  • Castaño-Yepes Jorge David
  • Amor-Quiroz D.A.
  Physica A: Statistical Mechanics and its Applications, Elsevier, 2020, 548, pp.123871. We examine the effect of non-equilibrium processes modeled by the introduction of a generalized Boltzmann factor on the thermal and magnetic properties of an array of two-dimensional GaAs quantum dots in the presence of an external uniform and constant magnetic field. The model consists of a single-electron subject to a confining Gaussian potential with a spin–orbit interaction in the Rashba approach. We compute the specific heat and the magnetic susceptibility within the formalism of χ2 -superstatistics from the exact solution of the Schrödinger equation. Furthermore, an analytic solution for the partition function allows a study of the impact of the number of subsystems on the superstatistical corrections and confirms that the ordinary thermo-magnetic properties are recovered whenever the thermal distribution can be approximated by a Dirac delta. Also, we found a progressive disappearance of the Schottky anomaly with decreasing number of subsystems, while the specific heat ceases to be a monotonically increasing function with respect to the average temperature when the χ2 -distribution is spread over a large range of temperatures. Remarkably, the introduction of fluctuations in the temperature is found to suppress the paramagnetic phase transition that would otherwise appear at low temperatures. Finally, we emphasize that an appropriate construction of the definition of physical observables is crucial for obtaining a correct description of the physics derived from a non-extensive construction of the entropy. (10.1016/j.physa.2019.123871)
  DOI : 10.1016/j.physa.2019.123871
• Topological invariants and the definition of energy in quadratic gravity theory
  
  • Giribet Gaston
  • Miskovic Olivera
  • Olea Rodrigo
  • Rivera-Betancour David
  Physical Review D, American Physical Society, 2020, 101 (6), pp.064046. We provide a simple method to compute the energy in higher curvature gravity in asymptotically AdS spacetimes in even dimensions. It follows from the combined use of topological terms added to the gravity action, and the Wald charges derived from the augmented action functional. No additional boundary terms are needed. As a consistency check, we show that the formula for the conserved quantities derived in this way yields the correct result for the mass of asymptotically AdS black holes. (10.1103/PhysRevD.101.064046)
  DOI : 10.1103/PhysRevD.101.064046
• Scalar sunset diagram at finite temperature with imaginary square masses
  
  • van Egmond Duifje Maria
  • Reinosa Urko
  Physical Review D, American Physical Society, 2020, 102 (3), pp.036013. We evaluate the finite temperature scalar sunset diagram with imaginary square masses, that appears in the Gribov-Zwanziger approach to Yang-Mills (YM) theory beyond one-loop order. Since YM theory at finite temperature is governed by center-symmetry and the Polyakov loop, we also include the possibility of a constant temporal background gauge field in the form of color-dependent imaginary chemical potentials. (10.1103/PhysRevD.102.036013)
  DOI : 10.1103/PhysRevD.102.036013
• Swampland, Gradient Flow and Infinite Distance
  
  • Kehagias Alex
  • Lüst Dieter
  • Lüst Severin
  Journal of High Energy Physics, Springer, 2020, 04, pp.170. In the first part of this paper we will work out a close and so far not yet noticed correspondence between the swampland approach in quantum gravity and geometric flow equations in general relativity, most notably the Ricci flow. We conjecture that following the gradient flow towards a fixed point, which is at infinite distance in the space of background metrics, is accompanied by an infinite tower of states in quantum gravity. In case of the Ricci flow, this conjecture is in accordance with the generalized distance and AdS distance conjectures, which were recently discussed in the literature, but it should also hold for more general background spaces. We argue that the entropy functionals of gradient flows provide a useful definition of the generalized distance in the space of background fields. In particular we give evidence that for the Ricci flow the distance ∆ can be defined in terms of the mean scalar curvature of the manifold, ∆ ∼ log $ \overline{R} $. For a more general gradient flow, the distance functional also depends on the string coupling constant.In the second part of the paper we will apply the generalized distance conjecture to gravity theories with higher curvature interactions, like higher derivative R$^{2}$ and W$^{2}$ terms. We will show that going to the weak coupling limit of the higher derivative terms corresponds to the infinite distance limit in metric space and hence this limit must be accompanied by an infinite tower of light states. For the case of the R$^{2}$ or W$^{2}$ couplings, this limit corresponds to the limit of a small cosmological constant or, respectively, to a light additional spin-two field in gravity. In general we see that the limit of small higher curvature couplings belongs to the swampland in quantum gravity, just like the limit of a small U(1) gauge coupling belongs to the swampland as well. (10.1007/JHEP04(2020)170)
  DOI : 10.1007/JHEP04(2020)170
• Shape dependence of renormalized holographic entanglement entropy
  
  • Anastasiou Giorgos
  • Moreno Javier
  • Olea Rodrigo
  • Rivera-Betancour David
  Journal of High Energy Physics, Springer, 2020, 09, pp.173. We study the holographic entanglement entropy of deformed entangling regions in three-dimensional CFTs dual to Einstein-AdS gravity, using a renormalization scheme based on the addition of extrinsic counterterms. In this prescription, when even- dimensional manifolds are considered, the universal contribution to the entanglement entropy is identified as the renormalized volume of the Ryu-Takayanagi hypersurface, which is written as the sum of a topological and a curvature term. It is shown that the change in the renormalized entanglement entropy due to the deformation of the entangling surface is encoded purely in the curvature contribution. In turn, as the topological part is given by the Euler characteristic of the Ryu-Takayanagi surface, it remains shape independent. Exploiting the covariant character of the extrinsic counterterms, we apply the renormalization scheme for the case of deformed entangling regions in AdS$_{4}$/CFT$_{3}$, recovering the results found in the literature. Finally, we provide a derivation of the relation between renormalized entanglement entropy and Willmore energy. The presence of a lower bound of the latter makes manifest the relation between the AdS curvature of the Ryu-Takayanagi surface and the strong subadditivity property. (10.1007/JHEP09(2020)173)
  DOI : 10.1007/JHEP09(2020)173
• Collectivity of heavy mesons in proton-nucleus collisions
  
  • Zhang Cheng
  • Marquet Cyrille
  • Qin Guang-You
  • Shi Yu
  • Wang Lei
  • Wei Shu-Yi
  • Xiao Bo-Wen
  Physical Review D, American Physical Society, 2020, 102 (3), pp.034010. Using a model based on the color glass condensate framework and the dilute-dense factorization, we systematically study the azimuthal angular correlations between a heavy flavor meson and a light reference particle in proton-nucleus collisions. The obtained second-harmonic coefficients (also known as the elliptic flows) for J/ψ and D0 agree with recent experimental data from the LHC. We also provide predictions for the elliptic flows of ϒ and B mesons, which can be measured in the near future at the LHC. This work can shed light on the physical origin of the collectivity phenomenon in the collisions of small systems. (10.1103/PhysRevD.102.034010)
  DOI : 10.1103/PhysRevD.102.034010
• Crossed beam energy transfer in the presence of laser speckle ponderomotive self-focusing and nonlinear sound waves
  
  • Hüller Stefan
  • Raj Gaurav
  • Rozmus Wojciech
  • Pesme Denis
  Physics of Plasmas, American Institute of Physics, 2020, 27 (022703). Crossed beam energy transfer, CBET, is investigated by taking into account the speckle structure of smoothed laser beams that overlap in a plasma with an inhomogeneous flow profile. Using the two-dimensional simulation code HARMONY, it is shown how ponderomotive self-focusing of laser speckles in crossing beams can significantly affect the transfer of energy from one beam to the other. The role of plasma flow on speckle self-focusing is investigated and revisited, in particular its consequences in terms of redirection and increasing angular spread of the laser beams due to beam bending and plasma-induced smoothing, respectively. At close-to-sonic flow the onset of self-focusing in the beam speckle structure occurs at considerably lower beam intensities than expected for the case without flow. CBET and speckle self-focusing can hence occur together when two crossed beams with equal frequency will resonantly exchange energy via their ponderomotively driven density perturbations flowing with sound speed. From the simulations it is found that consequences of ponderomotive self-focusing can be expected above an average intensity threshold scaling as I L ∼ 2 × 10 14 W cm −2 (λ 0 /1µm) −2 (T e /keV) with impact on the spatial and temporal coherence of the transmitted light. The density perturbations due to the ponderomotive force of the crossing beams can locally be enhanced in self-focusing speckles, partly leading to shock-like structures. These structures eventually increase the effect of plasma-induced smoothing and are at the origin of the stronger angular spread. (10.1063/1.5125759)
  DOI : 10.1063/1.5125759
• Conformally Soft Theorem in Gravity
  
  • Puhm Andrea
  Journal of High Energy Physics, Springer, 2020, 09, pp.130. A central feature of scattering amplitudes in gravity or gauge theory is the existence of a variety of energetically soft theorems which put constraints on the amplitudes. Celestial amplitudes which are obtained from momentum-space amplitudes by a Mellin transform over the external particle energies cannot obey the usual energetically soft theorems. Instead, the symmetries of the celestial sphere imply that the scattering of conformally soft particles whose conformal weights under the 4D Lorentz group SL(2, ℂ) are taken to zero obey special relations. Such conformally soft theorems have recently been found for gauge theory. Here, I show conformally soft factorization of celestial amplitudes for gravity and identify it as the celestial analogue of Weinberg’s soft graviton theorem. (10.1007/JHEP09(2020)130)
  DOI : 10.1007/JHEP09(2020)130
• Sextic tensor field theories in rank $3$ and $5$
  
  • Benedetti Dario
  • Delporte Nicolas
  • Harribey Sabine
  • Sinha Ritam
  Journal of High Energy Physics, Springer, 2020, 06, pp.065. We study bosonic tensor field theories with sextic interactions in d < 3 dimensions. We consider two models, with rank-3 and rank-5 tensors, and U(N)$^{3}$ and O(N)$^{5}$ symmetry, respectively. For both of them we consider two variations: one with standard short-range free propagator, and one with critical long-range propagator, such that the sextic interactions are marginal in any d < 3. We derive the set of beta functions at large N , compute them explicitly at four loops, and identify the respective fixed points. We find that only the rank-3 models admit melonic interacting fixed points, with real couplings and critical exponents: for the short-range model, we have a Wilson-Fisher fixed point with couplings of order $ \sqrt{\epsilon } $, in d = 3 − ϵ; for the long-range model, instead we have for any d < 3 a line of fixed points, parametrized by a real coupling g$_{1}$ (associated to the so-called wheel interaction). By standard conformal field theory methods, we then study the spectrum of bilinear operators associated to such interacting fixed points, and we find a real spectrum for small ϵ or small g$_{1}$. (10.1007/JHEP06(2020)065)
  DOI : 10.1007/JHEP06(2020)065
• Confronting same-sign W-boson production with parton correlations
  
  • Cotogno Sabrina
  • Kasemets Tomas
  • Myska Miroslav
  Journal of High Energy Physics, Springer, 2020, 10, pp.214. The future runs of LHC offer a unique opportunity to measure correlations between two partons inside the proton, which have never been experimentally detected. The process of interest is the production of two positively charged W-bosons decaying in the muon channel. We present a detailed analysis of proton-proton collisions at $ \sqrt{s} $ = 13 TeV, where we combine Monte Carlo event generators with our calculations of parton correlations. We carefully compare double parton scattering to relevant background processes and trace a path towards a clean signal sample. Several observables are constructed to demonstrate the effect of parton correlations with respect to clear benchmark values for uncorrelated scatterings. We find that especially spin correlations can be responsible for large effects in the variables we study, because of their direct relation with the parton angular momentum and, therefore, the directions of the muon momenta. We estimate the significance of the measurements as a function of the integrated luminosity and conclude that the LHC has the potential to detect, or put strong limits on, parton correlations in the near future. (10.1007/JHEP10(2020)214)
  DOI : 10.1007/JHEP10(2020)214