Search Results (6)

Conceivable explanations of Belle-II measurements of a (surprising) excess of missing energy decays of the B meson to the K meson not covered by standard model neutrino–antineutrino pairs might be offered by additional contributions of dark matter fermion–antifermion pairs. Assuming the excessive missing-energy events to be mediated by a (generic) scalar or vector boson, a simultaneous inspection of both the missing energy B decays into a pseudoscalar K meson or a vector $K^{\ast }$ meson enables to gain information on the nature of any boson relating the standard-model and dark-matter sectors, irrespective of (unknown) dark-sector details. Upon availability of indispensable experimental data, most prominent among such insights might be the identification of the mediator spin from the differential B-meson decay widths. Full article

The interaction between particles and their surrounding medium can induce a squeezed back-to-back correlation between particles and antiparticles. In this paper, the squeezed fermion back-to-back correlation (fBBC) for expanding sources is studied. The formulas of the fBBC correlation function of fermion–antifermion pairs for expanding sources are given. The expanding flow leads to a decrease in the fBBC of proton–antiproton pairs and $\Lambda$-$\overline{\Lambda }$ pairs in the high-momentum region, an increase in the fBBC in the low-momentum region, and a narrowing width of the fBBC varies with in-medium mass in the low-momentum region. Even though the expanding flow influences fBBC, the fBBC of proton–antiproton pairs and $\Lambda$-$\overline{\Lambda }$ pairs can still offer possible observation signals as the collision energy varies from a few GeV to 200 GeV. Full article

We investigate the interaction of fermion fields with oscillating domain walls, inspired by breather-type solutions of the sine-Gordon equation, a nonlinear system of fundamental importance. Our study focuses on the fermionic bound states and particle production induced by a time-dependent scalar background field. The fermions couple to two domain walls undergoing harmonic motion, and we explore the resulting dynamics of the fermionic wave functions. We demonstrate that while fermions initially form bound states around the domain walls, the energy provided by the oscillatory motion of the scalar field induces an outward flux of fermions and antifermions, leading to particle production and eventual flux propagation toward spatial infinity. Through numerical simulations, we observe that the fermion density exhibits quasiperiodic behavior, with partial recurrences of the bound state configurations after each oscillation period. However, the fermion wave functions do not remain localized, and over time, the density decreases as more particles escape the vicinity of the domain walls. Our results highlight that the sine-Gordon-like breather background, when coupled non-supersymmetrically to fermions, does not preserve integrability or stability, with the oscillations driving a continuous energy transfer into the fermionic modes. This study sheds light on the challenges of maintaining steady-state fermion solutions in time-dependent topological backgrounds and offers insights into particle production mechanisms in nonlinear dynamical systems with oscillating solitons. Full article

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of ${\pi }^0,\eta$, and ${\eta }^{\prime }$, and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions. Full article

In recent years, growing interest has been paid to the exploration of the concepts of entropy, heat and information, which are closely related to the symmetry properties of the physical systems in quantum theory. In this paper, we follow this line of research on the the validity of the concepts in quantum field theory by studying Landauer’s principle for a Dirac field interacting perturbatively with an Unruh–DeWitt detector in a $1+1$-dimensional MIT bag cavity. When the field is initially prepared in the vacuum state, we find that the field always absorbs heat, while the Unruh–DeWitt detector can either gain or lose entropy, depending on its motion status, as a result of the Unruh effect. When the field is initially prepared in the thermal state and the detector remains still, the heat transfer and entropy change can be obtained under two additional but reasonable approximations: (i) one is where the duration of the interaction is turned on for a sufficiently long period, and (ii) the other is where the Unruh–DeWitt detector is in resonance with one of the field modes. Landauer’s principle is verified for both considered cases. Compared to the results of a real scalar field, we find that the formulas of the vacuum initial state differ solely in the internal degree of freedom of the Dirac field, and the distinguishability of the fermion and anti-fermion comes into play when the initial state of the Dirac field is thermal. We also point out that the results for a massless fermionic field can be obtained by taking the particle mass $m\to 0$ straightforwardly. Full article

Kähler’s geometric approach in which relativistic fermion fields are treated as differential forms is applied in three spacetime dimensions. It is shown that the resulting continuum theory is invariant under global U$\left(N\right)\otimes$U$\left(N\right)$ field transformations and has a parity-invariant mass term, which are symmetries shared in common with staggered lattice fermions. The formalism is used to construct a version of the Thirring model with contact interactions between conserved Noether currents. Under reasonable assumptions about field rescaling after quantum corrections, a more general interaction term is derived, sharing the same symmetries but now including terms which entangle spin and taste degrees of freedom, which exactly coincides with the leading terms in the staggered lattice Thirring model in the long-wavelength limit. Finally, truncated versions of the theory are explored; it is found that excluding scalar and pseudoscalar components leads to a theory of six-component fermion fields describing particles with spin 1, with fermion and antifermion corresponding to states with definite circular polarisation. In the UV limit, only transverse states with just four non-vanishing components propagate. Implications for the description of dynamics at a strongly interacting renormalisation group fixed point are discussed. Full article