Searching for new physics at the frontiers with lattice quantum chromodynamics (original) (raw)

FLAG: Lattice QCD Tests of the Standard Model and Foretaste for Beyond

Proceedings of Flavor Physics & CP Violation 2015 — PoS(FPCP2015), 2016

After a short presentation of the FLAG collaboration, we review lattice results related to pion, K-, Dand B-meson physics with the aim of making them easily accessible to the particle-physics community. Only a selection of FLAG averages or estimates is presented. For light flavours, we present results on the form factor f + (0), arising in semileptonic K → π transition at zero momentum transfer, as well as the decay-constants f K , f π and their ratio. The consequences of these results for the CKM matrix elements |V us | and |V ud | are discussed. For heavy flavours we focus on Dand B-meson decay constants and form factors, as well as the CKM matrix elements |V cs |, |V cd | and |V ub |. In addition we briefly cover the recent advances stemming from the calculation the B K-parameters and touch upon related current results relevant to the Physics beyond the Standard Model, which will be the subject of the next FLAG edition.

Nuclear matrix elements from lattice QCD for electroweak and beyond-Standard-Model processes

Physics Reports, 2021

Over the last decade, numerical solutions of Quantum Chromodynamics (QCD) using the technique of lattice QCD have developed to a point where they are beginning to connect fundamental aspects of nuclear physics to the underlying degrees of freedom of the Standard Model. In this review, the progress of lattice QCD studies of nuclear matrix elements of electroweak currents and beyond-Standard-Model operators is summarized, and connections with effective field theories and nuclear models are outlined. Lattice QCD calculations of nuclear matrix elements can provide guidance for low-energy nuclear reactions in astrophysics, dark matter direct detection experiments, and experimental searches for violations of the symmetries of the Standard Model, including searches for additional CP violation in the hadronic and leptonic sectors, baryon-number violation, and lepton-number or flavor violation. Similarly, important inputs to neutrino experiments seeking to determine the neutrino-mass hierarchy and oscillation parameters, as well as other electroweak and beyond-Standard-Model processes can be determined. The phenomenological implications of existing studies of electroweak and beyond-Standard-Model matrix elements in light nuclear systems are discussed, and future prospects for the field toward precision studies of these matrix elements are outlined.

Physics of Heavy Quarks from Lattice QCD

2020

In the last few years, lattice QCD has made a dramatic progress in understanding the physics of hadrons containing heavy quarks, from the first principle. This review summarises the major achievements. I. INTRODUCTION Heavy quarks play a dominant role in the understanding of the weak interactions as well as of what may lie beyond the standard model. Since quarks are always bound into hadrons, and we do not understand the strong interactions rigorously, the results of these phenomena are often expressed in terms of non-perturbative parameters (also called matrix elements) that reflect our knowledge/ignorance of the strong interaction effects. Lattice QCD offers the best route to a non-perturbative determination of these parameters. The field of lattice gauge theories has nowadays achieved a maturity level where statistical errors are beaten down enough to expose systematic effects. This control over systematic effects has helped reliable extraction of matrix elements that allow us to...

Symmetries and Interactions from Lattice QCD

arXiv: High Energy Physics - Lattice, 2018

Precision experimental tests of the Standard Model of particle physics (SM) are one of our best hopes for discovering what new physics lies beyond the SM (BSM). Key in the search for new physics is the connection between theory and experiment. Forging this connection for searches involving low-energy hadronic or nuclear environments requires the use of a non-perturbative theoretical tool, lattice QCD. We present two recent lattice QCD calculations by the CalLat collaboration relevant for new physics searches: the nucleon axial coupling, gAg_AgA, whose precise value as predicted by the SM could help point to new physics contributions to the so-called "neutron lifetime puzzle", and hadronic matrix elements of short-ranged operators relevant for neutrinoless double beta decay searches.

Flavor Physics in the LHC era: the role of the lattice

We discuss the present status of global fits to the CKM unitary triangle using the latest experimental and theoretical constraints. For the required nonperturbative weak matrix elements, we use three-flavor lattice QCD averages from www.latticeaverages.org; these have been updated from Ref. [1] to reflect all available lattice calculations as of the "End of 2011". Because of the greater than 3 sigma disagreement between the extraction of |Vub| from inclusive and exclusive semileptonic b -> u l nu (l = e,mu) decays, particular emphasis is given to a clean fit in which we remove the information from these decays. Given current theoretical and experimental inputs, we observe an approximately 3 sigma tension in the CKM unitarity triangle that may indicate the presence of new physics in the quark-flavor sector. Using a model-independent parameterization of new-physics effects, we test the compatibility of the data with scenarios in which the new physics is in kaon mixing, in...

Lattice QCD inputs to the CKM unitarity triangle analysis

Physical Review D, 2010

We perform a global fit to the CKM unitarity triangle using the latest experimental and theoretical constraints. Our emphasis is on the hadronic weak matrix elements that enter the analysis, which must be computed using lattice QCD or other nonperturbative methods. Realistic lattice QCD calculations which include the effects of the dynamical up, down, and strange quarks are now available for all of the standard inputs to the global fit. We therefore present lattice averages for all of the necessary hadronic weak matrix elements. We attempt to account for correlations between lattice QCD results in a reasonable but conservative manner: whenever there are reasons to believe that an error is correlated between two lattice calculations, we take the degree of correlation to be 100%. These averages are suitable for use as inputs both in the global CKM unitarity triangle fit and other phenomenological analyses. In order to illustrate the impact of the lattice averages, we make Standard Model predictions for the parameters B K , |V cb |, and |V ub |/|V cb |. We find a (2-3)σ tension in the unitarity triangle, depending upon whether we use the inclusive or exclusive determination of |V cb |. If we interpret the tension as a sign of new physics in either neutral kaon or B-mixing, we find that the scenario with new physics in kaon-mixing is preferred by present data.

Chiral dynamics with strange quarks in the light of recent lattice simulations

Journal of High Energy Physics, 2011

Several lattice collaborations performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with standard N f = 3 chiral expansions at next-to-leading order, yielding low values of the quark condensate and/or the decay constant in the N f = 3 chiral limit. A reordering of these expansions seems required to analyse these data in a consistent way. We discuss such a reordering, known as Resummed Chiral Perturbation Theory, in the case of pseudoscalar masses and decay constants, pion and kaon electromagnetic form factors and K ℓ3 form factors. We show that it provides a good fit of the recent results of two lattice collaborations (PACS-CS and RBC/UKQCD). We describe the emerging picture for the pattern of chiral symmetry breaking, marked by a strong dependence of the observables on the strange quark mass and thus a significant difference between chiral symmetry breaking in the N f = 2 and N f = 3 chiral limits. We discuss the consequences for the ratio of decay constants F K /F π and the K ℓ3 form factor at vanishing momentum transfer.