Heavy Scalar Particles Research Articles

Towards automatic analytic evaluation of diagrams with masses

A method to calculate two-loop self-energy diagrams of the Standard Model is demonstrated. A direct physical application is the calculation of the two-loop electroweak contribution to the anomalous magnetic moment of the muon 1 2 (g−2) μ . Presently, we confine ourselves to a “toy” model with only μ, γ and a heavy neutral scalar particle (Higgs). The algorithm is implemented as a FORM-based program package. For generating and automatically evaluating any number of two-loop self-energy diagrams, a special C program has been written. This program creates the initial FORM-expression for every diagram generated by QGRAF, executes the corresponding subroutines and sums up the final results.

Gravitational interaction to one loop in effective quantum gravity

We carry out the first step of a program conceived, in order to build a realistic model, having the particle spectrum of the standard model and renormalized masses, interaction terms and couplings, etc. which include the class of quantum gravity corrections, obtained by handling gravity as an effective theory. This provides an adequate picture at low energies, i.e. much less than the scale of strong gravity (the Planck mass). Hence our results are valid, irrespectively of any proposal for the full quantum gravity as a fundamental theory. We consider only non-analytic contributions to the one-loop scattering matrix elements, which provide the dominant quantum effect at long distance. These contributions are finite and independent from the finite value of the renormalization counter terms of the effective lagrangian. We calculate the interaction of two heavy scalar particles, i.e. close to rest, due to the effective quantum gravity to the one loop order and compare with similar results in the literature.

Baryogenesis, dark matter and the width of the Z

We discuss a paradigm in which the generation of the observed quark-antiquark asymmetry is directly related to the origin of dark matter. In particular we consider a baryon-number conserving extension of the standard model by the addition of a weak isotriplet U(1) B -charged scalar field φ. We describe a scenario in which the out-of-equilibrium decay of heavy scalar particles preferentially produces quarks over antiquarks leading to the observed asymmetry. The excess baryon-number in the quark fields is exactly compensated by a net antibaryon-number in φ-particles. We focus on the consequences for both particle physics and cosmology and show that the mass of φ is very tightly constrained: 40 GeV ⪅ m φ ⪅50 GeV. We discuss accelerator signatures, the interaction of φ's with ordinary matter and implications for gf-particle detection. Finally we discuss some interesting cosmological phase transitions involving both U(1) B and the electroweak symmetry.

Rotational invariance in light-cone quantization.

In the study of the decay of a heavy scalar particle at rest in the Yukawa model at the one- and two-loop levels, it is shown explicitly that naive light-cone quantization leads to a violation of rotational invariance. Noncovariant counterterms are constructed in detail to restore Lorentz covariance. An analysis of surface and zero-mode contributions clarifies the origin of the problem.

Renormalization group equation in a theory with spontaneously broken symmetry and decoupling of heavy scalar particles

Renormalization group equations for light-particle processes are examined in a simple spontaneously broken symmetry theory (SBT) for energy-momentum far below a heavy scalar particle threshold. The results confirm the generalized decoupling theorem for SBT with the introduction of a new effective coupling constant.

Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino

We extend the Higgs mechanism in a supergauge invariant way. Spontaneous symmetry breaking occurs for all allowed values of the parameters of the scalar potential. With SU(2) × U(1) as gauge group and after spontaneous breaking of supergauge invariance, we obtain a model of weak and electromagnetic interactions for the electron and its neutrino, which includes also heavy leptons and scalar particles. The neutrino is the Goldstone fermion, associated with the photon in a massless vector multiplet.

Relativistic scalar quark model with strong binding

The dynamics of strong binding of heavy scalar particles (quarks) are discussed with the help of the Bethe-Salpeter equation with a smooth ladder-type kernel. For this purpose, the Bethe-Salpeter amplitudes are expanded intoO4 spherical functions and the remaining « hyper-radial » equation is solved by a variational method. These calculations are considered as a model of mesons as bound states of heavy quarks. The low-lying mesons form linear trajectories with a slope of 1 (GeV)−2. The modification of the vector-meson dominance form factor by the bound-state wave functions is calculated and found to be in good agreement with experiment.