The similarity renormalization group (SRG) is based on unitary transformations that suppress off-diagonal matrix elements, forcing the Hamiltonian toward a band-diagonal form. A simple SRG transformation applied to nucleon-nucleon interactions leads to greatly improved convergence properties while preserving observables and provides a method to consistently evolve many-body potentials and other operators. Progress on the nuclear many-body problem has been hindered for decades because nucleon-nucleon (NN) potentials that reproduce elastic-scattering phase shifts typically exhibit strong short-range repulsion as well as a strong tensor force. This leads to strongly correlated many-body wave functions and highly nonperturbative few-and many-body systems. But recent work shows how a cutoff on relative momentum can be imposed and evolved to lower values using renormalization group (RG) methods, thus eliminating the troublesome highmomentum modes [1,2]. The evolved NN potentials are energy-independent and preserve two-nucleon observables for relative momenta up to the cutoff. Such potentials, known generically as V low k , are more perturbative and generate much less correlated wave functions [2][3][4][5][6][7], vastly simplifying the many-body problem. However, a full RG evolution of essential few-body potentials has not yet been achieved.An alternative path to decoupling high-momentum from low-momentum physics is the similarity renormalization group (SRG), which is based on unitary transformations that suppress off-diagonal matrix elements, driving the Hamiltonian toward a band-diagonal form [8][9][10][11]. The SRG potentials are automatically energy independent and have the feature that high-energy phase shifts (and other high-energy NN observables), although typically highly model dependent, are preserved, unlike the case with V low k as usually implemented. Most important, the same transformations renormalize all operators, including many-body operators, and the class of transformations can be tailored for effectiveness in particular problems.Here we make the first exploration of SRG for nucleonnucleon interactions, using a particularly simple choice of SRG transformation, which nevertheless works exceedingly well. We find the same benefits of V low k : more perturbative interactions and lessened correlations, with improved convergence in few-and many-body calculations. The success of the SRG combined with advances in chiral effective field theory (EFT) [12,13] opens the door to the consistent construction and RG evolution of many-body potentials and other operators.The similarity RG approach was developed independently by Glazek and Wilson [8] Wegner's formulation in terms of a flow equation for the Hamiltonian. The initial Hamiltonian in the center-of-mass H = T rel + V , where T rel is the relative kinetic energy, is transformed by the unitary operator U (s) according towhere s is the flow parameter. This also defines the evolved potential V s , with T rel taken to be independent of s. Then H s evolves accor...

In this work the determination of low-energy bound states in quantum chromodynamics is recast so that it is linked to a weak-coupling problem. This allows one to approach the solution with the same techniques which solve electrodynamics: namely, a combination of weak-coupling diagrams and many-body quantum mechanics. The key to eliminating necessarily nonperturbative effects is the use of a bare Hamiltonian in which quarks and gluons have nonzero constituent masses rather than the zero rriasses of the current picture. The use of constituent masses cuts off the growth of the running coupling constant and makes it possible that the running coupling never leaves the perturbative domain. For stabilization purposes an artificial potential is added to the Hamiltonian, hut with a coefficient that vanishes a t the physical value of the coupling constant. The weak-coupling approach potentially reconciles the simplicity of the constituent quark model with tlie conlplexities of quantum chromodynamics. The penalty for achieving this perturbative picture is the necessity of formulating the dynamics of QCD in light-front coordinates and of dealing with the complexities of renormalization which such a fornlulation entails. We describe the reriormalization process first using a qualitative phase space cell analysis. and we then set up a precise similarity renormalization scheme with cutoffs on constituent mornenta and exhibit calculations to second order. We outline further computations that remain to be carried out. There is an initial nonperturbative but nonrelativistic calculation of the hadronic masses that deterirlines the artificial potential, with binding energies required to be fourth order in the coupling as in CJED. Next there is a calculation of the leading radiative corrections to these masses which requires our renornialization program. Then the real struggle of finding the right extensions to perturbation theorv to study the strong-coupling behavior of bound states can begin.PACS number(s): 11.1O.Ef. ll.lO.Gh, 1 2 . 3 8 . B~ I. I N T R O D U C T I O NT h e only truly successful approach t o bound states in field theory has been q u a n t u m electrodynamics ( Q E D ) . with its combination of nonrelativistic q u a n t u m mechanics t o handle b o u n d states a n d perturbation theory t o handle relativistic effects. Lattice gauge theory is nlaturing b u t has yet t o rival Q E D ' s comprehensive success. There are four barriers which prohibit a n approach t o q u a n t u m chromodynamics ( Q C D ) t h a t is analogous t o Q E D . T h e barriers a r e (1) t h e unlimited growth of t h e running coupling constant g in t h e infrared region.which invalidates perturbation theory, (2) confinement. which requires potentials t h a t diverge a t long distances as opposed t o t h e Coulombic potentials of perturbation theory. ( 3 ) spontaneous chiral symmetry breaking, which does not occur in perturbation theory. a n d (4) t h e nonperturbative structure of t h e Q C D vacuum. Contrasting t h e gloomy picture of t h e str...

Light-front theory may provide a promising avenue of research for nuclear and particle physics, but a Tamm-Dancoff truncation of field theory is required for practical computations. Such a truncation limits the number of virtual mesons allowed in hadronic field theories, or the number of quarks and gluons allowed in bound states described by quantum chromodynamics. Past Tamm-Dancoff renormalization problems are analyzed and a solution is proposed.Despite years of effort, strongly interacting relativistic systems are not understood. We are able to compute the properties of strongly interacting nonrelativistic systems using traditional methods from many-body quantum mechanics. Bound and scattering states of weakly interacting particles are well described by perturbative field theory. The major unsolved problem is that of the highly relativistic bound state. The main difficulties are far better understood now than they were in the 1940s when the effort to use field theory in the study of strong interactions began, but no practical tool has been developed for circumventing these difficulties. In this Letter we propose a path that leads around some of these problems and hopefully through the remainder, lightfront Tamm-Dancoff (LFTD). LFTD is simply the original Tamm-Dancoff approach 1,2 applied to light-front field theory. 3 The most closely related work is that of Brodsky, Lepage, Pauli, and collaborators. 4 Two key areas where the relativistic bound-state problem is central are nuclear physics and quantum chromodynamics (QCD). Consider first the problem of understanding the structure of light nuclei. At low energy and low resolution we can eliminate intermediate-and highenergy degrees of freedom, and describe nuclei using nonrelativistic nucleons interacting via potentials. As energy and resolution are increased we believe a limit is approached in which nuclei are systems of many highly correlated quarks and gluons, but there are many ways that this limit might be reached. In particular, there might be an intermediate regime where nonrelativistic models prove inadequate, but where relatively few hadronic degrees of freedom can be utilized to accurately describe both nuclear structure and response. 5 To determine if this is the case, one must have sufficiently accurate descriptions of strongly interacting hadronic systems. One-pion exchange is usually considered to be adequately described by potentials, so one really wants to push the description at least to the range of two-pion exchange. In this range it is not reasonable to consider pion exchange without including the fact that pions dress nucleons; nor does it make any sense to ignore the fact that pions interact with one another strongly. All strongly interacting degrees of freedom included in any problem should be allowed to fully interact with one another.Hamiltonian methods are extremely effective in describing systems of a few strongly interacting particles, and are immediately suggested by this problem.The second example is the problem of bound states of li...

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The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutroninduced interactions with the major actinides 235 U, 238 U and 239 Pu, on 241 Am and 23 Na, 59 Ni, Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy.