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Intersections of BSM Phenomenology and QCD for New Physics Searches (INT-15-3)
(INT Program September 14 - October 23, 2015)

Reported by Susan Gardner, Huey-Wen Lin, Felipe J. Llanes-Estrada, Ruth Van de Water
  Date posted December 7, 2015

The INT program Intersections of BSM Phenomenology and QCD for New Physics Searches was held in Seattle, Washington from Sept. 14-Oct. 23, 2015. The program was organized by Huey-Wen Lin (University of California, Berkeley), Susan Gardner (University of Kentucky), Felipe J. Llanes-Estrada (Universidad Complutense de Madrid), and Ruth Van de Water (Fermi National Accelerator Laboratory). The main purpose of the six-week program was to bring together theorists from the nuclear- and particle-physics communities to address key issues in the assessment of the QCD inputs needed to realize the next generation of low-energy precision experiments, with the end of identifying possible physics beyond the Standard Model. Such new-physics searches span a range of physics subfields, and we organized our program into themes that would collect them. Within these themes, we discussed ways in which lattice QCD, as well as other non- perturbative approaches, such as those employing ancillary experimental data and symmetries, could be used to sharpen windows on new physics from the existing and expected experimental results. Our program included

  • Searches for non-V-A interactions in weak decays and computations of nucleon charges pertinent to such searches

  • Searches for CP and T violation in light-quark systems, including searches for permanent electric dipole moments and QCD calculations of the needed hadronic matrix elements, as well as for T-odd decay correlations

  • Searches for baryon number violation, including neutron-antineutron oscillations and computations of related hadronic matrix elements

  • Investigations of dark-matter models and cosmologies with lattice QCD, as well as of WIMP-nucleon interactions within QCD

  • Searches for modifications of gravity and of fundamental constants accessible to nuclear physics

  • Investigations of hadronic contributions to g-2 of the muon and to the proton- radius puzzle

  • Searches for violations of lepton-flavor universality via light-hadron decays

  • Nuclear and hadronic matrix elements for the accelerator-based neutrino-physics program

  • Determinations of flavor-separated PDFs, as well as PDFs at large x and with applications to the LHC

  • Lattice QCD computations of PDFs and connections to global PDF fits

The program included a five-day workshop "QCD for New Physics at the Precision Frontier" during the third week of the program, Sept. 28-Oct. 2.

During the workshop week, it turned out that 10 presentations were given by female speakers (out of a total of 40), and 5 of those were review talks. During the last 2 days of week 2, we also held a mini-workshop on baryon number violation, with an emphasis on neutron-antineutron oscillations, providing a venue for experts to discuss recent work in depth.

During this program, we live-streamed a majority of the presentations through Adobe Connect and recorded podcasts for future viewing (if approved by the speaker). About 70 talks are now available from the program website, under the link "Talks online". We think the recordings will be very valuable for students and postdocs who want to do work in this direction and anticipate that, over the next few years, many more people will benefit from our investment. Several important new results were highlighted by and discussed in our program. These include computational advances in lattice QCD, for example, the remarkable new progress of the RBC Collaboration in their evaluation of the hadronic light-by-light (HLbL) contribution to the anomalous magnetic moment of the muon (with 5% statistical error at a near-physical pion mass). Even though there are systematic effects to be improved, the collaboration is on track to provide lattice-QCD input on the HLbL contribution needed for the interpretation of an improved experimental measurement. Another example is the detailed systematics and high-statistics (up to 65,000 measurements) study by the PNDME Collaboration, revealing that statistical fluctuations and unaccounted systematics are likely culprits in the puzzling inability of recent lattice-QCD calculations to reproduce the value of the nucleon axial charge measured in beta decay. Foundational advances in the application of effective field theory to the analysis of new-physics observables, such as the dark-matter (WIMP)-nucleon cross section, as well as of the permanent electric dipole moments of the neutron, nuclei, and atoms, that sharpen the connection of experimental searches to high- energy sources of new physics were also reported.

However, a number of problems remain, even after a few years of theoretical effort. For example, the mismatch between the proton radius extracted from the muonic hydrogen Lamb shift and from ordinary hydrogen spectroscopy (or electron-proton scattering data) has not been resolved. In addition, the flavored parton-distribution functions (PDFs) in the proton, such as the strange and anti-strange PDFs, remain poorly known even after recent global PDF analyses. One may look forward to future experiments or precision lattice QCD inputs to help resolve these issues.

We expect several new collaborations to emerge as a result of our program, as well as a number of publications in the near future resulting from discussion and interactions during the program. The subject is very active, with the expectation of new discoveries in years to come.