Two-loop leading-color helicity amplitudes for three-photon production at the LHC

We calculate all planar contributions to the two-loop massless helicity amplitudes for the process $$ q\overline{q} $$ q q ¯ → γγγ. The results are presented in fully analytic form in terms of the functional basis proposed recently by Chicherin and Sotnikov. With this publication we provide the two-loop contributions already used by us in the NNLO QCD calculation of the LHC process pp → γγγ [Chawdhry et al. (2019)]. Our results agree with a recent calculation of the same amplitude [Abreu et al. (2020)] which was performed using different techniques. We combine several modern computational techniques, notably, analytic solutions for the IBP identities, finite-field reconstruction techniques as well as the recent approach [Chen (2019)] for efficiently projecting helicity amplitudes. Our framework appears well-suited for the calculation of two-loop multileg amplitudes for which complete sets of master integrals exist.

Form factors for the Nucleon-to-Roper electromagnetic transition at large-Q2

We report on a recent calculation of all Roper-related electromagnetic transtions form factors, cov ering the range of energies that next-to-come planned experiments are expected to map. Direct reliable cal culations were performed, within a Poincaré covariant approach of the three-body bound-state problem, up to Q2/m2N=6; approximated then by applying the Schlessinger point method and the results eventually extended up to Q2/m2N ≃12 via analytic continuation.

Calculations ofη-nuclear quasi-bound states in few-body systems

We report on our Stochastic Variational Method (SVM) calculations ofη-nuclear quasi-bound states in s-shell nuclei as well as the very recent calculation of the p-shell nucleus6Li. TheηNpotentials used were constructed fromηNscattering amplitudes obtained within coupled-channel models that incorporateN*(1535) resonance. We found thatη6Li is bound in theηNinteraction models that yield ReaηN≥ 0.67 fm. Additional repulsion caused by the imaginary part ofηNpotentials shifts the onset ofη-nuclear binding toη4He, yielding very likely no quasi-bound state inη3He.

Resonances from lattice QCD

The spectrum of hadron is mainly composed as shortly-lived states (resonance) that decay onto two or more hadrons. These resonances play an important role in a variety of phenomenologically significant processes. In this talk, I give an overview on the present status of a rigorous program for studying of resonances and their properties using lattice QCD. I explain the formalism needed for extracting resonant amplitudes from the finite-volume spectra. From these one can extract the masses and widths of resonances. I present some recent examples that illustrate the power of these ideas. I then explain similar formalism that allows for the determination of resonant electroweak amplitudes from finite-volume matrix elements. I use the recent calculation of the πγ* → ππ amplitude as an example illustrating the power of this formalism. From such amplitudes one can determine transition form factors of resonances. I close by reviewing on-going efforts to generalize these ideas to increasingly complex reactions and I then give a outlook of the field.

Semiclassical approach for the evaporating black hole revisited

A recent calculation shows that the observed energy density in the Unruh state at the future event horizon as seen by a freely falling observer is finite if the observer is released from rest at any positive distance outside the horizon; however, it is getting larger and larger so that it is negatively divergent at the horizon in the limit that the observer starts falling from rest at the horizon, which corresponds to the infinite boost with respect to the freely falling observer at a finite distance from the horizon. In order to resolve some conflicts between the recent calculation and the conventional ones in the well-known literatures, the calculation of the free-fall energy density is revisited and some differences are pointed out.

Perturbative gravity from gauge theory

Here, we describe a recently conjectured duality between color and kinematics for gauge-theory amplitudes. Whenever this duality is manifest, the integrands of loop-level gravity scattering amplitudes can be obtained from corresponding gauge-theory amplitudes via a double-copy relation. This duality has been used to enormously simplify a number of explicit multiloop supergravity calculations. The results of these computations is that supergravity theories have a surprisingly tame ultraviolet behavior, and in some cases may even be finite. As an example, we summarize a recent calculation showing that half-maximal [Formula: see text] supergravity in four spacetime dimensions is ultraviolet finite at three loops, contrary to previous expectations.

SINGLE INCLUSIVE JET PRODUCTION IN PP COLLISION: DEPENDENCE ON JET ALGORITHM

We present a recent calculation of single-inclusive high-pT jet production in pp collisions at RHIC, when the initial protons are unpolarized and also when they are longitudinally polarized. We investigate the effect of the algorithm adopted to define the jets on the numerical results of cross sections and spin asymmetries.