Prof. Philip Mannheim, Department of Physics, University of Connecticut

Not one but two renormalizable theories of gravity

Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Minkowski path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be CPT symmetric. And when one continues the theory into the complex plane and uses the CPT symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Minkowski path integral now is well behaved, and the theory now can serve as a low energy effective theory. Consequently, the theory can now be offered as a fully consistent, unitary and renormalizable theory of quantum gravity. By analogous reasoning a pure fourth-order derivative theory is a fully consistent quantum gravity theory in its own right.

P. D. Mannheim, arXiv:2301.13029, Classical and Quantum Gravity 40, 205007 (2023); arXiv:2303.10827, Int. J. Mod. Phys. D 32, 2350096 (2023).

Masato Nagatsuka, KEK, the High Energy Accelerator Research Organization, Japan

Search for bound state formation in DD* and BB* channels using lattice QCD with a relativistic heavy quark action

A color-singlet combination of two heavy quarks and two light antiquarks is an attractive object in search for exotic hadrons. In particular, the doubly charmed tetraquark has been observed by LHCb and the doubly bottomed tetraquark is expected to have a deeply bound state. In this seminar, we address a scenario that the BB* channel has a shallow bound state based on our latest lattice simulations to explore the phase shifts of DD and BB* scattering. For this purpose, 2+1 flavor PACS-CS gauge ensembles with pion masses 295, 411 and 569 MeV are utilized and a relativistic heavy quark action is adopted for the charm and bottom quarks.

Dr. Ryan Abbott, MIT

Normalizing Flows for Lattice QCD

Normalizing flows have recently arisen as a potential tool for accelerating lattice field theory calculations. In this talk I will give an overview of how normalizing flows have been applied to field theories, in particular focusing on recent progress applying normalizing flows to lattice QCD as well as current efforts to scale flow models towards modern lattice field theory calculations.

Dr. Sebastian Schenk, University of Mainz

Quantum Imprint of the Anharmonic Oscillator

We discuss the anharmonic oscillator in quantum mechanics using exact WKB methods in a ‘t Hooft-like double scaling limit where classical behavior is expected to dominate. We compute the tunneling action in this double scaling limit, and compare it to the transition amplitude from the vacuum to a highly excited state. Our results, exact in the semiclassical limit, show that the two expressions coincide, apart from an irreducible and surprising instanton contribution. The semiclassical limit of the anharmonic oscillator betrays its quantum origin as a rule showing that the quantum theory is intrinsically gapped from classical behavior. Besides an example of a resurgent connection between perturbative and nonperturbative physics, this may provide a way to study transition amplitudes from tunnelling actions, and vice versa.

Note the special room: GS 413E

Dr. Fatma Aslan, Jefferson National Laboratory and UConn

Hadron structure-oriented approach to TMD phenomenology

We present a first practical implementation of a recently proposed hadron structure oriented (HSO) approach to TMD phenomenology applied to Drell-Yan like processes. We compare and contrast general features of our methodology with other common practices and emphasize the improvements derived from our approach that we view as essential for applications where extracting details of nonperturbative transverse hadron structure is a major goal. These include the HSO’s preservation of a basic TMD parton-model-like framework even while accounting for full TMD factorization and evolution, explicit preservation of the integral relationship between TMD and collinear PDFs, and the ability to meaningfully compare different theoretical models of nonperturbative TMD parton distributions.