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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 FY2018-Q3

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 charges gA, gS and gT from the 2+1+1-flavor clover-on-HISQ calculations was completed, including the analysis of the very time consuming second physical mass HISQ ensemble with lattice size 963 ×192 at 0.06 fm on cluster and GPU computers at Los Alamos, at OLCF and using ERCAP allocations at NERSC. A paper describing the results was prepared and submitted for publication to PRD. The final analysis of flavor diagonal axial and tensor charges was completed. A paper describing the contribution of quark spin to the proton spin was prepared and submitted for publication to PRL. 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 completed and manuscripts describing the results were worked on. Results will be presented by Rajan Gupta and Yong-Chull Jang at Lattice 2018.

Relevant References:
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 mixing with the pseudoscalar operator are ongoing. Investigations of gradient flow method to deal with the divergent renormalization and mixing problem of the cEDM operator were initiated. Analysis of data generated so far was carried out and results will be presented at Lattice 2018 by Tanmoy Bhattacharya.

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

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 nucleon sigma term and the strangeness content of the proton, and the interaction of dark matter with nucleons. These matrix elements get contributions from disconnected diagrams that are computationally challenging to compute with high precision. Bhattacharya, Gupta and Yoon worked on two manuscript describing the results of extensive simulations carried out over the last three years for publication. They have analyzed the chiral and continuum extrapolation for the contribution of the flavor diagonal charges for the first time. A paper describing the contribution of quark spin to the proton spin was prepared and submitted for publication to PRL. They are continuing to collaborate with Gambhir, Orginos and Stathopoulos at William and Mary to develop a new method based on deflation and hierarchical probing to speed up the calculation of disconnected diagrams.

Relevant References:

Transverse Momentum Distribution Functions

New simulations, in collaboration with the Regensburg group, are being done.

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

Behavior of QCD at finite temperature

Investigated the properties of QCD at finite temperature, including the nature of the transition, the equation of state and the fluctuations of conserved charges (electric charge, strangeness, baryon number) around the transition temperature (140–160 MeV) as part of the HOTQCD collaboration during the period 2007-2015. The six resulting publications have over 2500 citations.

Relevant References:
Physical Review D90 (2014) 094503
Physical Review Letters 113 (2014) 082001
Physical Review D86 (2012) 034509
Physical Review D86 (2012) 094503
Physical Review D85 (2012) 054503
Physical Review D80 (2009) 014504

Dark Matter and LHC Physics

Graesser is continuing to work on topological dark matter scenario and generalizing it in several directions. He is collaborating with J. Osinski, a University of New Mexico graduate student visiting Los Alamos for 6 months on a DOE Office of Science Graduate Student Research Award. They are exploring how the predictions for the relic dark matter density in such a scenario depends on the cosmological history prior to Big Bang Nucleosynthesis. A draft is in preparation for posting to the arXiv.

He is also continuing his work with Tuhin Roy (TATA) and Arun Thalapillil (Pune) on improving the sensitivity of the LHC to new TeV-scale physics scenarios.

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, in collaboration with V. Cirigliano, W. Dekens, J. de Vries, and E. Mereghetti, developed an effective field theory for lepton number violation (LNV) by 2 units, covering the large class of theories in which LNV mediators lie above the GeV scale. The new master formula for 0νββ decay supersedes all previous “master formulas” since it uses a minimal basis of operators and correct QCD RG equations; performs careful and systematic matching of quark operators onto the chiral theory of pions and nucleons; identifies all the needed LECs and includes their values where they are known; includes the leading effect dimension-5, dimension-7, and dimension-9 operators — including their interference terms — and includes non-perturbative renormalization of contact operators, a feature completely missed by all previous analyses. The team applied their master formula to obtain constraints on single LNV operators, and a number of benchmark points for the left-right symmetric model. For instance, in a particular bench mark set of mass parameters (mWR ~ 4.5 TeV, mνRi=1,2,3 ~ 10 GeV) – consistent with current LHC limits – they found that the induced dim-9 operators dominate over the active Majorana neutrino mass contributions and that this benchmark point is excluded by existing 0νββ decay limits, demonstrating the complementarily between LHC searches for LNV and neutrinoless double beta decay experiments. This work appeared as arXiv:1806.02780 and was submitted to JHEP.

Relevant References:
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

Daniele S. M. Alves has work in progress on: (i) Peccei-Quinn dynamics at the GeV scale; (ii) sterile neutrinos with Beyond the Standard Model interactions with quarks and leptons via light dark sector mediators; (iii) entanglement renormalization in effective field theories. Her paper on "A viable QCD axion in the MeV mass range" has been published in JHEP 1807 (2018) 092.

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