INT Program INT202b
BeyondtheStandardModel Physics with Nucleons and Nuclei
July 13  August 7, 2020
Update: Due to the COVID19 pandemic, the program plan has been revised accordingly to become a threeweek online virtual program July 13  31, 2020. Click for more info and seminar schedule.
Overview
In the next decade, an impressive experimental program will test the limits of the Standard Model
(SM) and address the most pressing open questions in particle physics, from the nature of dark
matter to the origin of neutrino masses, from the dominance of matter over antimatter in the
universe to the absence of strong CP violation and the large hierarchy between the electroweak and
the Planck scale. Searches for beyondtheSM (BSM) physics via lowenergy precision experiments
will play a crucial role in answering these questions, by looking, in particular, for deviations from
symmetry patterns of the SM. Prominent examples involving nuclear systems are searches for lepton
number violation via neutrinoless double beta decay, probes of CP violation via EDM experiments
with nucleons, nuclei, and diamagnetic atoms, and DM direct detection. Other experiments look for
proton decay, neutronantineutron oscillations, nonstandard chargecurrent interactions in neutron
and nuclear β decays, CPT violation, neutrinoscattering experiments, and the list goes on.
These experiments are complementary to highenery experiments such as the LHC or DUNE,
and share the common feature of probing highenergy physics by using nuclear targets. Their
interpretation involves physics on a large range of scales, from the eV and MeV scales of atomic and
nuclear physics, to the GeV scale where hadronization takes place, all the way to the (multi)TeV
scale where BSM physics potentially originates. In the present unfortunate situation of no hints
for any BSM signals at the LHC, lowenergy precision searches, where significant improvements in
sensitivity can be reached in relatively short time with relatively low costs, can take an even more
prominent place in the future of particle physics.
Background
A signal in many of the aforementioned experiments would be an unambiguous sign of BSM physics. To interpret such a signal (or limits) and to discriminate between different BSM models, we require solid theoretical control over a large range of energy scales. Ideally one has
 A modelindependent link to other searches for BSM physics such as collider and flavor observables.
A smooth transition between quarklevel and hadronic degrees of freedom, using an interplay of lattice QCD and effective field theory.
A consistent power counting to determine the hierarchy of contributions to nuclear processes such that nuclear wave functions and external currents can be calculated in a systematic expansion.

Sufficient control over nuclear theory once the power counting has determined the relevant interactions. For very light nuclei the scattering and boundstate equations can be solved essentially exactly, while for heavier (but still relatively light) systems ab initio methods have made great progress. Heavier systems that are often used in experiments, require nuclear manybody methods.
Program format
Overcoming these challenges requires a multidisciplinary approach. The first is typically associated to the particle physics community, the second and third to lattice QCD (LQCD) and chiral EFT practitioners, while the fourth is the domain of manybody nuclearstructure community. We therefore divide the program into 4 weeks, where each week has a theme where at least two communities overlap:
Week 1, (1317 July): From the TeV scale to QCD. Discussion of aims and motivations for nuclear precision experiments. Comparison to direct highenergy searches. Standard Model Effective Field Theory. LQCD calculations of nucleon observables such as nucleon charges and form factors, electric dipole moments, and lowenergy constants for neutrinoless double beta decay processes.
Week 2, (2024 July): From QCD to nucleons and light nuclei. Continuation of LQCD calculations of BSM observables, including twonucleon matrix elements, with the goal of identifying a list of key matrix elements for various BSM searches. Chiral EFT methods for BSM observables in two and fewnucleon systems. We will address the questions: Can we identify a consistent powercounting for BSM nuclear forces and currents? Can BSM matrix elements in very light nuclei, which can be computed without approximations, be used as benchmark points for more advanced methods such as QMC and NCSM?
Week 3, (2731 July): Towards ab initio methods. Further discussion of the BSM potentials and currents. Focus on how to implement them into firstprinciple nuclear calculations. How can we ensure proper renormalization? Do BSM potentials and currents need to be developed at the same order as the strong chiral potentials? Are ab initio methods mature enough to provide mediummass benchmark calculations for manybody methods?
Week 4, (37 August): Towards heavy nuclei. Many nuclear BSM experiments take advantage of heavy nuclei that can enhance certain observables such as DM detection (via coherent scattering) and EDMs (avoiding of Schiff screening), or where light nuclei are simply of no use (0νββ). Such nuclei pose severe theoretical challenges as the interpretation of data requires knowledge of nuclear matrix elements that cannot be measured. We will encourage exchange of ideas between the few and manybody communities, and try to identify observables and calculations that can provide robust tests of important nuclear matrix elements.