*Fifteenth Workshop on Non-Perturbative QCD*

11-14 June 2018

*Fifteenth Workshop on Non-Perturbative QCD*

11-14 June 2018

11-14 June 2018

Aspects of Large-D Matrix Models and SYK-like Physics”Recently the Sachdev-Ye-Kitaev (SYK) models and SYK-like tensor models have attracted great interest as holographic models reproducing some behaviors of near extremal black holes. In this presentation, I will introduce a new class of large-D limits for matrix models which have a connection with the SYK-like physics, and explain their physical properties.
Structure Constants of Twist-2 Operators in the triple Regge Limit”The structure constants of twist two operators in the triple BFKL limit are determined from the correlation function of three “color dipoles” in the triple Regge limit. The calculation is performed in $N=4$ SYM but the result is valid in other gauge theories such as QCD.
I will discuss the thermodynamical limit of conformal 4d Feynman diagrams spanning planar 2d square lattices. Such diagrams appear in the so-called fishnet theory, a matrix scalar theory which stands as a close relative of the N=4 Super-Yang-Mills theory and happens to be integrable in the planar limit. Using integrable techniques developed for studying the scaling dimensions of single trace operators in N=4 SYM, I will argue that the continuum limit of the fishnet diagrams is governed by the 2d AdS5 non-linear sigma model. This talk is based on a work done in collaboration with De-liang Zhong.
Topology and Theta Dependence in Nonabelian Gauge Theories: Recent Results from the Lattice”In recent times there has been a renewed interest in the lattice study of the theta dependence in nonabelian gauge theories and QCD in particular, triggered both by theoretical motivations and phenomenological applications to axion physics. We will give a review of the recently obtained results and of the problematics encountered in studying this subject by lattice methods.
Dual Space-Time of the SYK Model”We argue that the SYK model leads to a three dimensional dual theory in a suitable background. At strong coupling, a Horava-Witten compactification of one of the dimensions reproduces the SYK spectrum, and a non-standard propagator of the 3D theory exactly reproduces the two point function of the bilocal fields, including the leading finite coupling correction from the “zero mode”. We show that the space-time on which the bilocal field lives is not, however, the dual space-time in the sense of AdS/CFT duality – rather the bilocals are related to the dual fields by an integral transform.
We present our implementation of Numerical Stochastic Perturbation Theory for gauge theories coupled to fermions, and compute the infinite volume coefficients of the perturbataive expansion of the plaquette. We discuss the evidence for renormalon behaviour, which is usually associated to the gluon condensate, and determine the normalisation of the singularity in the Borel plane.
Excitations of D-branes are open strings that give rise to a gauge theory at lowenergy. In this talk we study the CFT that emerges on the world volume of thegiant graviton branes that condense to produce an LLM geometry.
Renormalization of non-Abelian QCD”In the time permitted, this can only be a qualitative description of our new (<8 years old) results in QCD. The underlying fact of our approach is that QCD is not just a “more complicated form of Abelian QED”, but is a completely and essentially different theory. And a successful prediction of QCD scattering provides an excellent demonstration of those differences.
Random tensors exhibit a new large N limit, the so called “melonic” limit. While non trivial, the melonic limit is much simpler than the planar limit of random matrices. It turn, in the large N limit tensor field theories generically exhibit a strongly interacting infrared fixed point. I will discuss on a particular example how, in the large N limit, this fixed point can be studied nonperturbatively in the IR relevant and marginal (in the neighborhood of the fixed point) couplings.
”A main difficulty in understanding the dynamics of jets produced in the high-density environment of ultrarelativistic heavy ion collision, is to provide a unified description for the two sources of radiation that are a priori expected: the “vacuum-like’’ emissions triggered by the parton virtualities and the “medium-induced’’ emissions generated via collisions in the surrounding medium. In this talk, I will argue that these two mechanisms can be factorized from each other within a controlled, “double-logarithmic’’, approximation. The vacuum-like cascadesdevelop at early times and exhibit angular ordering due to color coherence, like the standard parton showers in the vacuum. The effect of the medium can be simply formulated as a kinematic constraint which limits the phase-space for vacuum-like radiation and thus reduces the parton multiplicities. The gluons produced by these cascades lose their mutual coherence via multiple scattering and thus act as independent sources of energy loss via medium-induced radiation. This simple picture derived from first-principles offers a natural interpretation for the LHC data on jet fragmentation in Pb+Pb collisions.
Floquet Sperconductor in Holography”I will talk about constructing nonequilibrium steady states in a holographic superconductor under time periodic driving by an external rotating electric field. There are first and second order phase transitions depending on the amplitude and frequency of the external source. In particular, the system exhibits a first order transition inside the superconducting phase which is suggested to exist all the way down to zero temperature. To obtain the dynamical phase diagram, nonequilibrium thermodynamic potential for such steady solutions is discussed from the holographic point of view. This talk is based on arXiv:1804.06785.
We give an overview of Bi-local Holography applicable in Vectorial AdS/CFT correspondence. Mappings from bi-local space to AdS bulk space-time are realized in momentum space through double Fourier transforms. Bi-local diagrams are seen to translate into Conformal partial wave expansions and Witten diagrams of AdS. Sum rules for conformal blocks are deduced.
Thermalization in Holographic Confining Theories”Time dependent perturbations of states in the holographic dual of a 3+1 dimensional confining theory are considered. The perturbations are induced by varying the coupling to the theory’s most relevant operator. The dual gravitational theory belongs to a class of Einstein-dilaton theories which exhibit a mass gap at zero temperature and a first order deconfining phase transition at finite temperature. The perturbation is realized in various thermal bulk solutions by specifying time dependent boundary conditions on the scalar, and we solve the fully backreacted Einstein-dilaton equations of motion subject to these boundary conditions. We compute the characteristic time scale of many thermalization processes, noting that in every case we examine, this time scale is determined by the imaginary part of the lowest lying quasi-normal mode of the final state black brane. We quantify the dependence of this final state on parameters of the quench, and construct a dynamical phase diagram. Further support for a universal scaling regime in the abrupt quench limit is provided.
Transverse-Momentum Dependence of Gluon Distributions at Small x”Transverse-momentum-dependent (TMD) gluon distributions have different operator definitions, depending on the process under consideration. Using the Color Glass Condensate (CGC) framework, we study that aspect of TMD factorization in the small-x limit, for various unpolarized TMD gluon distributions encountered in the literature. We show how to express those in terms of CGC correlators of Wilson lines, while keeping Nc finite. We then proceed to evaluate them by solving the JIMWLK equation numerically. We obtain that at large transverse momentum, the process dependence essentially disappears, while at small transverse momentum, non-linear saturation effects impact the various TMD gluon distributions in very different ways.
“The Schwarzian and Black Hole Physics”In this talk, I will discuss the Schwarzian theory (relevant for low-energy SYK physics and Jackiw-Teitelboim gravity) from a 2d perspective. I will demonstrate how Schwarzian quantum mechanics is naturally embedded in 2d Liouville CFT. This perspective allows a direct computation of Schwarzian two- and four-point functions. Out-of-time ordered (OTO) four-point functions are also determined using the 2d R-matrix. The semi-classical limit of these expressions demonstrate various aspects of black holes, such as quasi-normal modes and eikonal shockwave expressions in the holographic bulk. Mostly based on arXiv:1705.08408
Tensor Models for Black Hole Probes”The infrared dynamics of the SYK model, as well as its associated tensor models, exhibit some of the non trivial features expected of a holographic dual of near extremal black holes. These include developing certain symmetries of the near horizon geometry and exhibiting maximal chaos. In this paper we present a generalization of these tensor models to include fields with fewer tensor indices and which can be thought of as describing probes in a black hole background. In large N limit, dynamics of the original model remain unaffected by the probe fields and some of the four point functions involving probe fields exhibit maximal chaos, a non trivial feature expected of a black hole probe.
Is there a conformal QCD?” The spacelike-timelike conformal correspondence between decays and certain spacelike wavefunctions is reviewed. A (partially successful) attempt to follow Gell Mann and Low in defining a conformal QCD by removing parts of self energy graphs in a particular gauge is described.
The Deep Underground Neutrino Experiment (DUNE) provides a rich science program with the focus on the neutrino oscillation physics, proton decay studies and Supernova explosions. The high-intensity wide-band neutrino beam will be produced at Fermilab and will be directed to the 40 kt Liquid Argon far detector at the Sanford Underground Research Facility (SURF), 1300 km from Fermilab. One of the most important goals of the experiment is to determine the neutrino mass ordering and the measurement of the CP violating phase. The underground location of the large DUNE far detector and its excellent energy and spatial resolution will allow also conducting non-accelerator physics programs predicted by GUT models, such as nucleon decay or n-nbar oscillations. Moreover, it will be sensitive to measure of the electron neutrino flux from a core-collapse supernova providing valuable information on the mechanism of a supernova. This ambitious project involves worldwide contribution and extensive prototyping and testing program to guarantee that all parts of the technology are fully understood and well tested. Two such prototypes, in both single phase (ProtoDUNE-SP) and dual phase (ProtoDUNE-DP) technologies, are under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018
Remarks on Jet Production and Odderon in the Multi-Regge Limit”We will discuss the multi-Regge limit in QCD, highlighting multijet production at the LHC and Odderon exchange in elastic scattering.
Quantum magnets have effective description in terms of gauge theories. Some of these have features similar to QCD. A famous CP(N-1) model is a model of spin chains, asymptotically free and allows for a theta-angle. Others, such as the 3D monopole plasma, are both effective theories of 3D quantum magnets and 4D circle-compactified QCD-like theories. In particular cases, both QCD and quantum magnets have strong constraints on their low energy physics due to ‘t Hooft anomalies of their global symmetries, which must be matched. I will discuss some such manifestations and their consequences.
I will discuss our results for central production of meson ($\pi^+ \pi^-$, $K^+ K^-$) and baryon ($p \bar p$, $Lambda \bar \Lambda$) pairs as well as mesonic resonances (scalar and tensor) in central diffractive (double-pomeron exchange) processes. The calculation is performed within exact $2 \to 4$ kinematics using tensor pomeron model proposed recently by Nachtmann et al. Several differential distributions will be presented. The results are relevant for experiments being carried out at the LHC and RHIC.
Analytic formula for non-perturbative QCD is derived. Gauge Invariance is insured through Gauge Independence. The resulting formulation is finite and exact. A renormalization scheme is presented such that comparison with experiments can be performed. For ease of computation, the 2 particle quark quark scattering in the Eikonal regime is chosen. The results are compared with elastic proton-proton scattering at the ISR and LHC regimes.
Recent advances on anomaly matching elucidates that the topology of QFT can constrain the possible phase diagram more strongly than we have thought. We show that QCD with massless fundamental quarks has not only the perturbative chiral anomaly but also the anomaly involving two-form gauge fields. As an application, we consider “Z3-QCD”, which is the QCD with the twisted quark boundary condition, and show that some of symmetries must be broken at any circle radius (“temperatures”) and quark chemical potentials.
Using an effective Lagrangian approach, valid in the double large-N and chiral limit (with $r_i \sim m_iN /\Lambda$ fixed), we determine the regions in the multidimensional parameter space of the $r_i$ where CP is spontaneously broken/unbroken at $\theta=\pi$. The two regions are separated by an hypersurface on which lines of first order transitions end, there is a massless pseudoscalar meson (in spite of chiral symmetry being explicitly broken), and the topological susceptibility of QCD diverges. When we add to the model a generic axion field (in order to ensure CP at all values of $\theta$) the above considerations have a bearing on the shape of the axion potential near the boundary of its periodicity interval. This may have implications on the calculation of axionic dark matter abundance if some $r_i$ have a marked temperature dependence as one approaches $T_c$.
We study the feasibility to extract the leading twist pion distribution amplitude (DA) and the higher twist normalization constant from suitably chosen Euclidean correlation functions with two local currents at a spacelike separation. This position space approach is complementary to the calculation of the lowest moments of the DA using the Wilson operator product expansion and avoids mixing with lower dimensional local operators on the lattice. We will highlight similarities and differences to closely related methods that use quasi- or pseudo-distributions.
The Beyond Complex Langevin approach, presented during the previous meeting, has been improved and extended. In particular the physics behind the negative eigenvalues of the Minkowski action is now understood. As a consequence the simple method to represent oscillating, complex weights by positive distribution, has been found and successfully applied to gaussian systems in different-dimensions.
Holographic descriptions of gauge theories have been well studied so far. In this talk, we discuss deformations of gauge theories by employing the Yang-Baxter (YB) deformation technique. This is a systematic way to study integrable deformations of 2D integrable non-linear sigma models and it is applicable to type IIB string theory on AdS_5 x S^5. The resulting deformed backgrounds, including the well-known examples such as Lunin-Maldacena background and Maldacena-Russo background,should be dual to deformed gauge theories via AdS/CFT. In particular, this YB deformation is closely related to non-commutative gauge theories and we show that the non-commutativities satisfy a universal divergence formula with a certain vector field, which indicates a generalization of the standard supergravity.
Complex Langevin Simulations of a Finite Density Matrix Model for QCD” We study the Stephanov model, which is a Random Matrix Theory model for QCD at finite baryon density, using the Complex Langevin algorithm. Naive implementation of the algorithm shows convergence towards the phase quenched or quenched theory rather than to the intended theory with dynamical quarks. A detailed analysis of this issue various potential resolutions of the failure of this algorithm are discussed. |