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Theoretical Physics Quarterly Progress Reports

Investigating the field of high energy physics through experiments that strengthen our fundamental understanding of matter, energy, space, and time.

Los Alamos HEP Theory Quarterly Report FY2019-Q2

Daniele Alves, Tanmoy Bhattacharya, Michael L. Graesser, Rajan Gupta

The primary areas of activity of the theory group are in physics beyond the Standard Model, cosmology, dark matter, lattice quantum chromodynamics, neutrinos, the fundamentals of quantum field theory and gravity, and particle astrophysics. The questions pursued by this group relate to deep mysteries in our understanding of Nature at the level of the Standard Model and beyond. The main tools we use are quantum field theory and General Relativity.

Lattice QCD

The Los Alamos Lattice QCD team and their collaborators are carrying out precision studies investigating signatures of new physics at the TeV scale, Novel CP violating operator's contribution to nEDM, elucidating the structure of the nucleon, and neutrino-nucleon interactions. Progress during this quarter on these projects is described below. The team is also actively working on Quantum Information and Computing under the DOE call "Quantum Information Science Enabled Discovery for High Energy Physics".

Nucleon charges and form-factors

The analysis of isovector and flavor diagonal charges, gA, gS and gT, from the 2+1+1-flavor clover-on-HISQ calculations was completed and results published in three papers in PRD. The analysis of electric, magnetic and axial vector form factors using up to 3-state fits for both the 2+1+1-flavor clover-on-HISQ and 2+1-flavor clover on clover lattice QCD formulations was carried out and manuscripts describing the results are in final stages of preparation. Gupta completed and submitted manuscripts for two plenary review talks at Spin 2018 and co-authored the FLAG 2019 review on nucleon matrix elements. The FLAG report was finalized and submitted for publication in this period.

Relevant References:
FLAG Review arXiv:1902.08191
Physical Review D98 (2018) 094512 arXiv:1806.10604
Physical Review D98 (2018) 091501 arXiv:1808.07597
Physical Review D98 (2018) 034503 arXiv:1806.09006
Physical Review D96 (2017) 114503 arXiv:1705.06834
Physical Review D95:5 (2017) 074508
Physical Review D94:5 (2016) 054508
Physical Review D93:11 (2016) 114506
Physical Review D92:9 (2015) 094511
Physical Review D89:9 (2014) 094502
Physical Review D85:5 (2012) 054512.

Matrix elements of novel CP violating operators and nEDM

Calculations of the matrix elements of the quark chromo electric dipole moment operator (cEDM) and its mixing with the pseudoscalar operator, and of the Theta and Weinberg terms are on going. Preliminary results using a variance reduction method developed by us show a factor of ten reduction in errors. Investigations of gradient flow method to deal with the divergent renormalization and mixing problem of the cEDM and Weinberg operators are continuing.

Relevant References:
Physical Review D92:9 (2015) 114026
Physical Review Letters 112:21 (2015) 212002

Contributions from Disconnected diagrams

The matrix elements of flavor diagonal operators are needed for the analysis of a number of interesting qualities such as the nucleon electric dipole moment, the quark contribution to the nucleon spin, the nucleon sigma term and the strangeness content of the proton, and the interaction of dark matter with nucleons. These matrix elements also get contributions from disconnected diagrams, that are computationally challenging to compute with high precision. Bhattacharya, Gupta and Yoon published two manuscript describing the results (quark contribution to proton spin and neutron EDM) of extensive simulations carried out over the last three years. Developed the calculation of the renormalization factors needed for flavor diagonal operators. With these in hand, the analyses of disconnected contributions on five Wilson-clover ensembles have also been started.

Relevant References:
Physical Review D98 (2018) 094512 arXiv:1806.10604
Physical Review D98 (2018) 091501 arXiv:1808.07597

Transverse Momentum Distribution Functions

New simulations, in collaboration with the Regensburg group, are continuing.

Relevant References:
Physical Review D96 (2017) 094508 arXiv:1706.03406

Dark Matter and LHC Physics

Graesser and UNM graduate student Jacek Osinski are finishing a manuscript on the impact that non-trivial cosmologies in the early history of the Universe may have on scenarios for topological dark matter. During this time period, Graesser started a new direction of research. He is investigating the constraints magnetars may place on axion and hidden sector monopole models for dark matter.

Relevant References:
Physics Letters B749 (2014) 293
Physical Review Letters111 (2013) 121802
JHEP 1302(2013) 046
JHEP 1210(2012) 025
Physics Letters B714 (2012) 267
Physics Review D85 (2012) 054512
JHEP 1110(2011) 110

Michael Graesser: Neutrinoless double beta decay

Graesser continued his research into the neutrinoless double beta decay process nn-> pp ee, extending previous work to next-to-leading order in the chiral expansion. A manuscript is being completed. The neutrinoless double beta decay process (NDBD) is an important probe of any beyond-the-Standard-Model physics that violates lepton number by two units. NDBD provides a critical constraint on Majorana neutrino masses for active neutrinos, interactions of sterile/right-handed neutrinos, and on general classes of multi-TeV physics violating lepton number by two units. An important theoretical program is to use chiral effective theory to systematically describe how such high-energy physics, including Majorana neutrino masses, contribute to the NDBD process.

Relevant References:
Journal of High Energy Physics12 (2018) 097 arXiv:1806.02780
Physical Review Letters 120:20 (2018) 202001 arXiv:1802.10097
Journal of High Energy Physics12 (2017) 82 arXiv:1708.09390
Journal of High Energy Physics (2017)99
Physics Letters B769 (2017) 460

Daniel S. M. Alves

During the past quarter, Daniele Alves has worked on two projects: (1) extension of the neutrino sector to include sterile neutrinos interacting with matter via light mediators; exploration of these models to address short-baseline neutrino anomalies. (2) Extension of entanglement renormalization methods to continuous effective field theories; exploration of numerical implementations via wavelet transform techniques.

Relevant References:
Journal of High Energy Physics 07 (2018) 92 arXiv:1710.03764