Nuclear Theory·nucl-th

Thursday·October 10, 2024

15 papers—8 primary·7 cross-listed

09
Tunnelling amplitudes through localised external potentials from Feynman diagram summation
Rosemary Zielinski🇦🇺 · Cedric Simenel🇦🇺 · Patrick McGlynn🇦🇺
Currently there is no general theory of quantum tunnelling of a particle through a potential barrier which is compatible with QFT. We present a complete calculation of tunnelling amplitudes for a scalar field for some simple potentials using quantum field-theoretic methods. Using the perturbative S-matrix formalism, starting with the Klein-Gordon Lagrangian, we show that an infinite summation of Feynman diagrams can recover tunnelling amplitudes consistent with relativistic quantum mechanics. While this work does not include many-particle effects arising from a fully quantised QFT, it is necessary to investigate QFT corrections to tunnelling amplitudes.
↳ hep-thnucl-thEPJC(2024)·5 citations
10
Quantum corrections to tunnelling amplitudes of neutral scalar fields
Rosemary Zielinski🇦🇺 · Patrick McGlynn🇦🇺 · Cedric Simenel🇦🇺
Though theoretical treatments of quantum tunnelling within single-particle quantum mechanics are well-established, at present, there is no quantum field-theoretic description (QFT) of tunnelling. Due to the single-particle nature of quantum mechanics, many-particle effects arising from quantum field theory are not accounted for. Such many-particle effects, including pair-production, have proved to be essential in resolving the Klein-paradox. This work seeks to determine how quantum corrections affect the tunnelling probability through an external field. We investigate a massive neutral scalar field, which interacts with an external field in accordance with relativistic quantum mechanics. To consider QFT corrections, we include another massive quantised neutral scalar field coupling to the original via a cubic interaction. This study formulates an all-order recursive expression for the loop-corrected scalar propagator, which contains only the class of vertex-corrected Feynman diagrams. This equation applies for general external potentials. Though there is no closed-form analytic solution, we also demonstrate how to approximate the QFT corrections if a perturbative coupling to the quantised field is assumed.
↳ hep-thnucl-thEPJC(2024)·3 citations
11
QCD deconfinement transition line up to $μ_{B} = 400$ MeV from finite volume lattice simulations
Szabolcs Borsanyi🇩🇪 · Zoltan Fodor🇩🇪 · Jana N. Guenther🇩🇪 · Paolo Parotto🇮🇹 · Attila Pasztor🇭🇺 · Ludovica Pirelli🇩🇪 · Kalman K. Szabo🇩🇪 · Chik Him Wong🇩🇪
The QCD cross-over line in the temperature ( $T$ ) -- baryo-chemical potential ( $μ_{B}$ ) plane has been computed by several lattice groups by calculating the chiral order parameter and its susceptibility at finite values of $μ_{B}$ . In this work we focus on the deconfinement aspect of the transition between hadronic and Quark Gluon Plasma (QGP) phases. We define the deconfinement temperature as the peak position of the static quark entropy ( $S_{Q} (T, μ_{B})$ ) in $T$ , which is based on the renormalized Polyakov loop. We extrapolate $S_{Q} (T, μ_{B})$ based on high statistics finite temperature ensembles on a $1 6^{3} \times 8$ lattice to finite density by means of a Taylor expansion to eighth order in $μ_{B}$ (NNNLO) along the strangeness neutral line. For the simulations the 4HEX staggered action was used with 2+1 flavors at physical quark masses. In this setup the phase diagram can be drawn up to unprecedentedly high chemical potentials. Our results for the deconfinement temperature are in rough agreement with phenomenological estimates of the freeze-out curve in relativistic heavy ion collisions. In addition, we study the width of the deconfinement crossover. We show that up to $μ_{B} \approx 400$ MeV, the deconfinement transition gets broader at higher densities, disfavoring the existence of a deconfinement critical endpoint in this range. Finally, we examine the transition line without the strangeness neutrality condition and observe a hint for the narrowing of the crossover towards large $μ_{B}$ .
↳ hep-lathep-phnucl-thPRD(2024)·28 citations
12
Relations Between Anomalous Dimensions in the Regge Limit
Ira Z. Rothstein🇺🇸 · Michael Saavedra🇺🇸
We extend the recent formalism developed for computing rapidity anomalous dimension of form factors using unitarity to the problem of high-energy near forward scattering. By combining the factorization of $2 \to 2$ scattering in the effective field theory (EFT) for Glauber operators with definite signature amplitudes, we derive an expression that relates anomalous dimensions (including Regge trajectories) to cut amplitudes, leading to significant computational simplifications. We demonstrate this explicitly by computing the one and two-loop Regge trajectories. Our formalism can also be used to bootstrap anomalous dimensions of operators not related by symmetries. As an example, we show that the full anomalous dimensions (including both the Regge pole and cut pieces) of the two Glauber operator anti-symmetric octet operator, can be determined from the anomalous dimension of the single Glauber exchange operator. Many other such relations exist between other color channels at each order in $α$ .
↳ hep-phhep-thnucl-thJHEP(2025)·8 citations
13
Magnetic coupling through flux branching of adjacent type-I and -II superconductors in a neutron star
K. H. Thong · A. Melatos
The inner and outer cores of neutron stars are believed to contain type-I and -II proton superconductors, respectively. The type-I superconductor exists in an intermediate state, comprising macroscopic flux-free and flux-containing regions, while the type-II superconductor is flux-free, except for microscopic, quantized flux tubes. Here, we show that the inner and outer cores are coupled magnetically, when the macroscopic flux tubes subdivide dendritically into quantized flux tubes, a phenomenon called flux branching. An important implication is that up to $\sim 1 0^{12} (r_{1} /1 0^{6} cm) erg$ of energy are required to separate a quantized flux tube from its progenitor macroscopic flux tube, where $r_{1}$ is the length of the macroscopic flux tube. Approximating the normal-superconducting boundary as sharp, we calculate the magnetic coupling energy between a quantized and macroscopic flux tube due to flux branching as a function of, $f_{1}$ , the radius of the type-I inner core divided by the radius of the type-II outer core. Strong coupling delays magnetic field decay in the type-II superconductor. For an idealised inner core containing only a type-I proton superconductor and poloidal flux, and in the absence of ambipolar diffusion and diamagnetic screening, the low magnetic moments ( $≲ 1 0^{27} G c m^{3}$ ) of recycled pulsars imply $f_{1} ≲ 1 0^{- 1.5}$ .
↳ astro-ph.HEcond-mat.quant-gascond-mat.supr-congr-qc+1MNRAS(2024)·2 citations
14
A New-Old Approach to Composite Scalars with Chiral Fermion Constituents
Christopher T. Hill🇺🇸
We develop a dynamical, Lorentz invariant theory of composite scalars in configuration space consisting of chiral fermions, interacting by the perturbative exchange of a massive "gluon" of coupling $g_{0}$ and mass $M_{0}^{2}$ (the coloron model). The formalism is inspired by, but goes beyond, old ideas of Yukawa and the Nambu-Jona-Lasinio (NJL) model. It yields a non-pointlike internal wave-function of the bound state, $ϕ (r)$ , which satisfies a Schrödinger-Klein-Gordon (SKG) equation with eigenvalue $μ^{2}$ . For super-critical coupling, $g_{0} > g_{0 c}$ , we have $μ^{2} < 0$ leading to spontaneous symmetry breaking. The binding of chiral fermions is semiclassical, and not loop-level as in NJL. The mass scale is determined by the interaction as in NJL. We mainly focus on the short-distance, large $M_{0}^{2}$ limit, yielding an NJL pointlike interaction, but the bound state internal wave-function, $ϕ (r)$ , remains spatially extended and dilutes $ϕ (0)$ . This leads to power-law suppression of the induced Yukawa and quartic couplings and requires radically less fine-tuning of a hierarchy than does the NJL model. We include a discussion of loop corrections of the theory. A realistic top--condensation model appears possible.
↳ hep-phhep-exhep-thnucl-thNPB(2025)·3 citations
15
Exclusive rare semileptonic decays of $B$ and $B_{c}$ mesons in the relativistic independent quark model
Kalpalata Dash🇮🇳 · P. C. Dash🇮🇳 · R. N. Panda🇮🇳 · Susmita Kar🇮🇳 · N. Barik🇮🇳
We investigate the exclusive rare semileptonic decays: $B (B_{c}) \to K (D_{(s)}) l l ˉ /Σ ν_{l} ν_{l} ˉ$ ( $l = μ, τ$ ) in the framework of relativistic independent quark (RIQ) model based on an average flavor independent confining potential in equally mixed scalar-vector harmonic form. The invariant weak form factors, parametrising the matrix elements between participating meson states are calculated in the parent meson rest frame. The momentum transfer dependence of the form factors is reliably determined in the whole accessible kinematical range: $q_{min}^{2} \leq 0 \leq q_{ma x}^{2}$ . Our predicted branching fractions for $B \to K μ^{+} μ^{-} / τ^{+} τ^{-} (Σ ν_{l} ν_{l} ˉ)$ , $B_{c} \to D (D_{s}) μ^{+} μ^{-}$ , $B_{c} \to D (D_{s}) τ^{+} τ^{-}$ and $B_{c} \to D (D_{s}) Σ ν_{l} ν_{l} ˉ$ , obtained in order of $1 0^{- 7} (1 0^{- 6})$ , $1 0^{- 9} (1 0^{- 7})$ , $1 0^{- 9} (1 0^{- 8})$ and $1 0^{- 8} (1 0^{- 7})$ , respectively are in reasonable agreement with other Standard Model predictions and Lattice QCD results. The averaged values of the lepton polarization asymmetries for decay modes are obtained as $⟨ P_{L} (B \to K μ^{+} μ^{-})⟩$ =-0.97, $⟨ P_{L} (B_{c} \to D_{(s)} μ^{+} μ^{-})⟩$ =-0.972, $⟨ P_{L} (B \to K τ^{+} τ^{-})⟩$ =-0.224, $⟨ P_{L} (B_{c} \to D τ^{+} τ^{-})⟩$ =-0.275 and $⟨ P_{L} (B_{c} \to D_{s} τ^{+} τ^{-})⟩$ =-0.194.
↳ hep-phnucl-thPRD(2024)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE

Tunnelling amplitudes through localised external potentials from Feynman diagram summation

Quantum corrections to tunnelling amplitudes of neutral scalar fields

QCD deconfinement transition line up to μB​=400 MeV from finite volume lattice simulations

Relations Between Anomalous Dimensions in the Regge Limit

Magnetic coupling through flux branching of adjacent type-I and -II superconductors in a neutron star

A New-Old Approach to Composite Scalars with Chiral Fermion Constituents

Exclusive rare semileptonic decays of B and Bc​ mesons in the relativistic independent quark model

Affiliations

QCD deconfinement transition line up to $μ_{B} = 400$ MeV from finite volume lattice simulations

Exclusive rare semileptonic decays of $B$ and $B_{c}$ mesons in the relativistic independent quark model