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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 2014-01

Tanmoy Bhattacharya, Alexander Friedland, Michael L. Graesser, Rajan Gupta, Emil Mottola, Michael S. Warren

The theory group is active in a number of diverse areas of research. Their primary areas of interest 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. Generally the questions pursued by this group relate to deep mysteries in our understanding of Nature at the boundaries of the Standard Model and the grammar we use to describe it–quantum field theory and General Relativity. The theory group continues to make advances at the forefront of research in these areas.

Lattice QCD

The Los Alamos Lattice QCD team and their collaborators are carrying out four precision studies investigating signatures of new physics at the TeV scale, elucidating the structure of the nucleon, and understanding QCD at finite temperature. Progress on these four projects is described below.

Nucleon charges and form-factors

Bhattacharya, Gupta, Yoon and their external collaborators (the PNDME collaboration) has reanalyzed the calculation of renormalization constants and the effect of smearing the lattices to reduce short distance noise. Based on better understanding, they are revising the manuscript (arXiv:1306.5435) in which they probe novel scalar and tensor interactions at the TeV scale by calculating matrix elements of scalar and tensor quark bilinears within a nucleon state. They have also developed the codes to do these calculations on cluster and GPU computers at Los Alamos and have started the analysis of the largest 643×144 lattices at the weakest coupling there.

Matrix elements of novel CP violating operators and nEDM

Bhattacharya, Cirigliano and Gupta are carrying out the analysis of the mixing and renormalization of novel CP violating operators that contribute to the Neutron Electric Dipole Moment. They have determined an operator basis that allows for off-shell renormalization using external fixed momentum states, and a paper describing the one-loop matching between MSbar and a renormalization independent scheme is in progress. The numerical calculations have been started in collaboration with the RBC group using resources provided by the national USQCD initiative.

Behavior of QCD at finite temperature

Bhattacharya and Gupta are continuing the statistical analysis of the entire data set generated by the full HotQCD collaboration to determine the equation of state. The final data analysis is expected to be completed by March 2014. They have also contributed to the analysis and writing of the manuscript on the deconfinement transition and U(1) axial anomaly using Domain Wall fermions being prepared for publication in PRL using domain wall fermions.

Disconnected diagrams and Transverse Momentum Distribution Functions

Bhattacharya, Gupta and Yoon, in collaboration with Michael Engelhardt, have started testing the computer programs to investigate signal in both connected and disconnected diagrams that will be needed to evaluate the Sivers function and other transverse momentum distribution functions. These calculations are being done on computing resources at JLab.

Improving searches for new particles at the LHC

Graesser and LANL post-doc Jinrui Huang continue to investigate whether a top squark lighter than the top quark is allowed by all data. In this scenario the light top squarks decay through three-body and possibly four-body decay channels. That is, top squarks decaying into b quark, on-shell W and neutralino and/or decaying into b quark, stau and neutralino final states are being investigated. In addition to constraining this scenario using data from direct searches for top squark and chargino/neutralino/stau pair production, Graesser and Huang are investigating constraints arising from the top quark pair production cross-sections measured at both the LHC and the Tevatron. Preliminary results indicate the good agreement between the theoretical prediction for the top pair production—now known to NNLO—and experimental measurements provides an important constraint on the bW-neutralino final state, though less so on the stau final states.

Precision Cosmology Simulations

At the Supercomputing '13 conference, Warren reported on improvements made over the past two decades to his adaptive treecode N-body method (HOT). A mathematical and computational approach to the cosmological N-body problem was described, with performance and scalability measured up to 256k (218) processors. We presented error analysis and scientific application results from a series of more than ten 69 billion particle cosmological simulations. These results include the first simulations using the new constraints on the standard model of cosmology from the Planck satellite.

Reference: M. S. Warren, 2HOT: An Improved Parallel Hashed Oct-tree N-body Algorithm for Cosmological SimulationProceedings of SC13: International Conference for High Performance Computing, Networking, Storage and Analysis,2013 (Best paper finalist).

Quantum Field Theory and Gravity

Mercator Fellowship at the Univ. of Jena, Germany

From Oct. to Dec., 2013 Mottola was a visiting Mercator Fellow supported by the DFG (German Science Foundation) at the Friedrich Schiller Universität in Jena, Germany. He gave several lectures to Ph. D. students there and co-organizer a workshop on Strongly Interacting Field Theories” at Jena, Nov. 14–16, 2013. Several new collaborations were begun with Prof. A. Wipf, M. Ansorg, H. Gies,and F. Karbstein in both the Theoretical Physics and Relativity groups at Jena.

Partly as a result of these collaborations, Mottola has been nominated for a Humboldt Fellowship in Germany.

While in Europe, Mottola also visited Profs. G. Dvali and V. Mukhanov at the Ludwig Maximillian Univ., Munich, Germany, Profs. J. Berges and J. Pawlowski at the Univ. of Heidelberg, and Prof. I. Antoniadis at CERN. In addition collaborations were continued by meeting with Prof. C. Corianò of the Univ. of Salento, Italy at both Jena and CERN.

The following invited seminars were given during this three month period:

  • The Instability of de Sitter Space and the Schwinger Effect,” Theoretisch-Physikalisches Institut, Friedrich Schiller Univ., Jena, Germany, Nov. 6, 2013.
  • Scalar Boson Condensates and Macroscopic Effects of the Quantum Conformal Anomaly,” Workshop on Strongly-Interacting Field Theories, Friedrich Schiller Univ., Jena, Germany, Nov. 14–16, 2013.
  • Scalar Condensates and Macroscopic Effects of the Quantum Conformal Anomaly,” A. Sommerfeld Ctr. for Theoretical Physics seminar, Ludwig Maximilian Univ., Munich, Germany, Nov. 25, 2013.
  • Instability of de Sitter Space, the Schwinger Effect and Dynamical Dark Energy,” CERN, TH seminar, Geneva, Switzerland, Dec. 2, 2013.
  • What's the (Quantum) Matter with Black Holes?,” Theoretisch-Physikalisches Institut, Friedrich Schiller Univ., Jena, Germany, Dec. 12, 2013.
  • What's the (Quantum) Matter with Black Holes?,” U. Heidelberg, Theoretical Physics seminar, Heidelberg, Germany, Dec. 20, 2013.

Quantum Effects in Gravitational Collapse

Our Letter (with R. Vaulin of MIT Kavli Institute) was published in Physics Today. In it we explained to a general physics readership that the widespread belief that gravitational collapse leads inevitably to an event horizon need not be correct when quantum effects are taken into account. Large vacuum stresses on the horizon are the result of standard one-loop calculations of quantum fluctuations in black hole spacetimes and are a generic feature of states which approach the ordinary Minkowski vacuum far from the black hole. Moreover if quantum fluctuations and associated stress-energies do become large at the apparent horizon (defined locally) of a forming black hole, then very general arguments lead one to expect that a critical surface or phase transition should occur in its vicinity. At such a phase boundary layer the energy density of the squeezed vacuum ρV can increase very rapidly. A positive value of the vacuum energy with negative pressure pV=−ρV in the interior of a black hole” then acts as a repulsive core, preventing further collapse. The resulting stable, non-singular endpoint of complete gravitational collapse, consistent with all quantum principles is a gravitational vacuum condensate star (gravastar), so named because its interior support relies upon the energy of a vacuum condensate ρV, with the same equation of state (though with a much larger magnitude) as the cosmological dark energy believed to be pervading our universe. Once large quantum backreaction effects at the horizon are admitted, with a phase boundary layer taking its place instead, the very basis of the Hawking thermal evaporation and black hole entropy, from which all the black hole paradoxes that arise when ℏ≠0, are eliminated, and there is no enormous quantum information loss to be accounted for. This provides a testable alternative first suggested in 2001 and discussed in the last few years in the firewall” papers.