Today I have deposited my PhD Thesis, titled “A Glance into Flavour Physics with Effective Field Theories and Machine Learning”.

Xiao Liu, Yan-Qing Ma

Abstract: AMFlow is a Mathematica package to numerically calculate dimensionally regularized Feynman integrals via the recently proposed auxiliary mass flow method, which sets up and solves differential equations of Feynman integrals with respect to an auxiliary mass parameter. Differential equations can be automatically computed using existed reduction packages. Boundary conditions can be calculated within the auxiliary mass flow framework. The differential equations are then solved numerically using generalized power series expansion method combining with numerical fit strategy. The main usages of the AMFlow package are discussed through an explicit example of double-box family involved in two-loop \(t\bar{t}\) production.

Link

See also: arXiv:2201.11636, arXiv:2201.11637

Zhi-Feng Liu, Yan-Qing Ma

Abstract: We find surprisingly that all Feynman integrals (FIs), with any number of loops, can be determined without doing integration. The only needed information are linear relations between FIs. Therefore, FIs computation is conceptually changed to a linear algebraic problem. Examples up to 5 loops are given to verify our observation. See also See also: arXiv:2201.11636, arXiv:2201.11669

Zhi-Feng Liu, Yan-Qing Ma

Abstract: We proposed a recipe to systematically calculate Feynman integrals containing linear propagators using the auxiliary mass flow method. The key of the recipe is to introduce an quadratic term for each linear propagator and then using differential equations to get rid of their effects. As an application, we calculated all master integrals of vacuum integrals containing a gauge link up to 4 loops, and we checked the results by nontrivial dimensional recurrence relations.

See also arXiv:2201.11637, arXiv:2201.11669

Shikma Bressler, Federico De Vito Halevy, Yosef Nir

Abstract: The \(R(D^{(*)})\) puzzle stands for a \(\sim3\sigma\) violation of lepton flavor universality between the decay rates of \(B\to D^{(*)}\tau\nu\) and \(B\to D^{(*)}\ell\nu\), where \(\ell=e,\mu\). If it is accounted for by new physics, there is no reason in general that the relevant neutrinos are, respectively, \(\nu_\tau\) and \(\nu_\ell\). We study whether the \(\tau\) related rate could be enhanced by significant contributions from \(B\to D^{(*)}\tau\nu_\ell\). We find the upper bounds from forbidden or rare meson decays imply that the contributions from the lepton flavor violating processes account for no more than about \(4\%\) of the required shift. Yet, no fine-tuned flavor alignment is required for the new physics. Searching for the related high-\(p_T\) process \(pp\to\tau^\pm\mu^\mp\) can at present put a lower bound on the scale of the lepton flavor violating new physics that is a factor of \(2.2\) weaker than the bound from meson decays.

Luigi Delle Rose, Benedict von Harling, Alex Pomarol

Abstract: We show how to simplify the calculation of the finite contributions from heavy particles to EFT Wilson coefficients by using on-shell methods. We apply the technique to the one-loop calculation of \(g-2\) and \(H\gamma\gamma\), showing how finite contributions can be obtained from the product of tree-level amplitudes. In certain cases, due to a parity symmetry of these amplitudes, the total contribution adds up to zero, as previously found in the literature. Our method allows to search for new natural zeros, as well as to obtain non-zero contributions in a straightforward way.

Sally Dawson, Pier Paolo Giardino

Abstract: Electroweak precision observables (EWPO) measured at the W and Z poles provide stringent limits on possible beyond the Standard Model physics scenarios. In an effective field theory (EFT) framework, the next-to-leading order QCD and electroweak results for EWPO yield indirect limits on possible 4-fermion operators that do not contribute to the observables at tree level. Here we calculate the next-to-leading corrections to EWPO induced by flavor non-universal 4-fermion interactions and find that the extracted limits on EFT coefficients have a strong dependence on the flavor structure of the 4-fermion operators.

Philip Bechtle, Cristin Chall, Martin King, Michael Kraemer, Peter Maettig, Michael Stoeltzner

Abstract: Experiments in particle physics have hitherto failed to produce any significant evidence for the many explicit models of physics beyond the Standard Model (BSM) that had been proposed over the past decades. As a result, physicists have increasingly turned to model-independent strategies as tools in searching for a wide range of possible BSM effects. In this paper, we describe the Standard Model Effective Field Theory (SM-EFT) and analyse it in the context of the philosophical discussions about models, theories, and (bottom-up) effective field theories. We find that while the SM-EFT is a quantum field theory, assisting experimentalists in searching for deviations from the SM, in its general form it lacks some of the characteristic features of models. Those features only come into play if put in by hand or prompted by empirical evidence for deviations. Employing different philosophical approaches to models, we argue that the case study suggests not to take a view on models that is overly permissive because it blurs the lines between the different stages of the SM-EFT research strategies and glosses over particle physicists’ motivations for undertaking this bottom-up approach in the first place. Looking at EFTs from the perspective of modelling does not require taking a stance on some specific brand of realism or taking sides in the debate between reduction and emergence into which EFTs have recently been embedded.

David London

Abstract: At the present time, there are hints of new physics (NP) in several observables involving \(b \to c \ell^- {\bar\nu}_\ell\) decays. In this talk, I describe measurable angular distributions for \({\bar B} \to D^* \mu^- {\bar\nu}_\mu\) and \({\bar B} \to D^* \tau^- (\to \pi^- \nu_\tau) {\bar\nu}_\tau\) decays, including the most general NP contributions. These angular distributions contain enough information to pin down the Lorentz structure of the NP, which will help to identify it. They also have the ability to reveal the presence of non-SMEFT (non-decoupling) NP.

Torben Ferber, Anastasiia Filimonova, Ruth Schäfer, Susanne Westhoff

Abstract: At colliders, neutral long-lived particles can be detected through displaced decay products or as missing energy. Which search strategy is better depends on the particle’s decay length just as on the detector properties. We investigate the complementarity of displaced and invisible signatures for the Belle II experiment. Focusing on axion-like particles \(a\) produced from meson decays, we present a new search strategy for two-body decays \(B^+ \to K^+ a, a\to E\!\!\!/\) with missing energy \(E\!\!\!/\). With \(50\,\)ab\(^{-1}\) of data, Belle II can probe light invisible resonances with branching ratio \(\mathcal{B}(B^+\to K^+ a) \gtrsim 10^{-7}\) and decay length \(c\tau_a \gtrsim 1\,\)m. For axion-like particles, we expect the sensitivity of \(B^+ \to K^+ E\!\!\!/\) to small couplings to improve by up to two orders of magnitude compared to previous searches at collider and fixed-target experiments. For sub-GeV particles, \(B^+ \to K^+ E\!\!\!/\) at Belle II and searches at beam-dump experiments are most sensitive; for heavier particles, searches for displaced vertices at Belle II, long-lived particle experiments at the LHC, and future fixed-target experiments can probe the smallest couplings.