Nuclear Theory·nucl-th

Friday·April 5, 2019

5 papers—1 primary·4 cross-listed

02
From the Standard Model towards a Theory of Matter: Quarks
T. Goldman · G. J. Stephenson · Jr
We follow the example of Cabibbo by revising the Standard Model (SM) to present a universal mass structure for fermions. A universal Higgs coupling for each species of fundamental fermions moves the SM towards a Theory of Matter, albeit without correctly describing the observed mass spectrum. It exposes a need for a complete Theory of Matter to include components from physics beyond the Standard Model (BSM). Describing the effect of these components phenomenologically provides a means to infer the nature of some of the BSM physics required. Our results also provide constraints on some BSM matrix elements. Here we apply this concept to quarks; the application to leptons will appear in a separate paper. An immediate benefit for theory is the reduction of the largest fine structure constant for the Higgs coupling to fermions by an order of magnitude, which improves the perturbative appearance of the weak interactions. The small mixing of the third generation of each fermion in the fermion families to the others is attributed to the small BSM perturbations that produce the small mass ratio of the lighter generations to the most massive one.
↳ hep-phnucl-th0 citations
03
Decay $X (3872) \to π^{0} π^{+} π^{-}$ and $S$ -wave $D^{0} D ˉ^{0} \to π^{+} π^{-}$ scattering length
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
The isospin-breaking decay $X (3872) \to (D^{*} D ˉ + D ˉ^{*} D) \to π^{0} D D ˉ \to π^{0} π^{+} π^{-}$ is discussed. In its amplitude there is a triangle logarithmic singularity, due to which the dominant contribution to $B R (X (3872) \to π^{0} π^{+} π^{-})$ comes from the production of the $π^{+} π^{-}$ system in a narrow interval of the invariant mass $m_{π^{+} π^{-}}$ near the value of $2 m_{D^{0}} \approx 3.73$ GeV. The analysis shows that $B R (X (3872) \to π^{0} π^{+} π^{-})$ can be expected at the level of $1 0^{- 3}$ -- $1 0^{- 4}$ . This estimate includes, in particular, the assumption that the $S$ -wave inelastic scattering length $∣ α_{D^{0} D ˉ^{0} \to π^{+} π^{-}}^{''} ∣ \approx 1/ (2 m_{D^{*+}}) \approx 0.25 \mbox G e V^{- 1}$ .
↳ hep-phhep-exnucl-thPRD(2019)·15 citations
04
Testing the strength of the $U_{A} (1)$ anomaly at the chiral phase transition in two-flavour QCD
Bastian B. Brandt🇩🇪 · Marco Cè🇩🇪 · Anthony Francis🇩🇪 · Tim Harris🇨🇭 · Harvey B. Meyer🇮🇹 · Owe Philipsen🇩🇪 · Hartmut Wittig🇩🇪
We study the thermal transition of QCD with two degenerate light flavours by lattice simulations using $O (a)$ -improved Wilson quarks. Particular emphasis lies on the pattern of chiral symmetry restoration, which we probe via the static screening correlators. On $3 2^{3}$ volumes we observe that the screening masses in transverse iso-vector vector and axial-vector channels become degenerate at the transition temperature. The splitting between the screening masses in iso-vector scalar and pseudoscalar channels is strongly reduced compared to the splitting at zero temperature and is actually consistent with zero within uncertainties. In this proceedings article we extend our studies to matrix elements and iso-singlet correlation functions. Furthermore, we present results on larger volumes, including first results at the physical pion mass.
↳ hep-lathep-phnucl-thPoS(2019)·13 citations
05
Shear viscosity of classical fields in scalar theory
Hidefumi Matsuda🇯🇵 · Teiji Kunihiro🇯🇵 · Akira Ohnishi🇯🇵 · Toru T. Takahashi🇯🇵
We investigate the shear viscosity of massless classical scalar fields in the $ϕ^{4}$ theory on a lattice by using the Green-Kubo formula. Based on the scaling property of the classical field, the shear viscosity is represented using a scaling function. Equilibrium expectation value of the time-correlation function of the energy-momentum tensor is evaluated as the ensemble average of the classical field configurations, whose time evolution is obtained by solving the classical equation of motion starting from the initial condition in thermal equilibrium. It is found that there are two distinct damping time scales in the time-correlation function, which is found to show damped oscillation behavior in the early stage around a slow monotonous decay with an exponential form, and the slow decay part is found to dominate the shear viscosity in the massless classical field theory. This kind of slow decay is also known to exist in the molecular dynamics simulation, then it may be a generic feature of dense matter.
↳ cond-mat.stat-mechhep-phnucl-thPTEP(2020)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

From the Standard Model towards a Theory of Matter: Quarks

Decay X(3872)→π0π+π− and S-wave D0Dˉ0→π+π− scattering length

Testing the strength of the UA​(1) anomaly at the chiral phase transition in two-flavour QCD

Shear viscosity of classical fields in scalar theory

Affiliations

Decay $X (3872) \to π^{0} π^{+} π^{-}$ and $S$ -wave $D^{0} D ˉ^{0} \to π^{+} π^{-}$ scattering length

Testing the strength of the $U_{A} (1)$ anomaly at the chiral phase transition in two-flavour QCD