Anomalous Decay of Heavy Fermions by Electroweak Instanton

1997 ◽  
Vol 12 (19) ◽  
pp. 3365-3381
Author(s):  
Keyan Yang
Keyword(s):  
Minkowski Space ◽  
Potential Barrier ◽  
Effective Potential ◽  
Heavy Fermion ◽  
Higgs Mass ◽  
Heavy Fermions ◽  
Semiclassical Approximation ◽  
Critical Value ◽  
Fermion Mass ◽  
Fermion Number

The presence of a heavy fermion doublet in the electroweak instanton probably leads to unsuppressed fermion number nonconservation. By calculating numerically the effective potential barrier of electroweak instanton with heavy fermion in Minkowski space by using semiclassical approximation, it is shown that, if the mass of heavy fermion exceeds a critical value [Formula: see text] TeV (for MH = MW), the tunneling by electroweak instanton should be unsuppressed and the heavy fermion decays with fermion number violation. The dependence of critical fermion mass on the Higgs mass is also presented.

scholarly journals CJT effective potential approach to analyze the nature of phase transition of thermal QED$$_3$$ at finite volume

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Yi Hu ◽  
Hong-tao Feng
Keyword(s):  
Phase Transition ◽  
Finite Volume ◽  
Effective Potential ◽  
Chiral Limit ◽  
Critical Value ◽  
Second Order ◽  
Fermion Mass ◽  
Infinite Volume ◽  
Second Order Transition ◽  
Volume Size

AbstractBased on the Cornwall–Jackiw–Tomboulis effective potential and the truncated Dyson–Schwinger equations, the nature of phase transition of thermal QED$$_3$$ 3 at finite volume is investigated. We show that, with the rise of temperature, the system undergoes a second-order transition in the chiral limit, and remains exhibiting the second-order with small fermion mass, while it switches to a crossover when the fermion mass exceeds a critical value about $$m_{c}$$ m c , which diminishes with the increasing volume size and tends to zero in infinite volume.

The nucleation of vorticity by ions in superfluid 4 He I. Basic theory

1984 ◽  
Vol 311 (1518) ◽  
pp. 433-467 ◽  
Keyword(s):  
High Pressure ◽  
Potential Barrier ◽  
Superfluid Helium ◽  
Recent Observation ◽  
Critical Value ◽  
Vortex Loop ◽  
Quantum Tunnelling ◽  
Vortex Loops ◽  
Very High ◽  
Vortex Nucleation

A theory is developed of vortex nucleation by an ion moving in superfluid helium at a low temperature. It is shown that production of a vortex loop attached to the side of the ion becomes energetically possible when the velocity of the ion exceeds a critical value, but that nucleation is impeded by the presence of a small potential barrier. The predicted critical velocity is close to that observed experimentally, at least at high pressure. Nucleation of an encircling vortex ring, considered some years ago by Schwarz & Jang (Phys.Rev. A8,3199 (1973)), probably becomes possible only at a higher velocity, and it is impeded by a large potential barrier. It is shown that for vortex loops the potential barrier can probably be overcome at a rate consistent with experiment either by quantum tunnelling at the lowest temperatures or thermally, by absorption of a single roton, at higher temperatures. Possible explanations of the recent observation by Bowley et al . {Phil. Trans. R. Soc. Lond. A307, 201 (1982)) that at high pressure the rate of vortex nucleation falls off at very high velocities are discussed.

scholarly journals A Lattice Test of Alternative Interpretations of "Triviality" in (λΦ4)4 Theory

1997 ◽  
Vol 12 (14) ◽  
pp. 1011-1024 ◽  
Author(s):  
A. Agodi ◽  
G. Andronico ◽  
P. Cea ◽  
M. Consoli ◽  
L. Cosmai ◽  
...  
Keyword(s):  
Phase Transition ◽  
Effective Potential ◽  
Higgs Mass ◽  
Higgs Field ◽  
Alternative Interpretation ◽  
Lattice Data ◽  
First Order ◽  
Conventional Picture ◽  
The Continuum ◽  
Second Order Phase Transition

There are two physically different interpretations of "triviality" in (λΦ4)4 theories. The conventional description predicts a second-order phase transition and that the Higgs mass mh must vanish in the continuum limit if v, the physical vev is held fixed. An alternative interpretation, based on the effective potential obtained in "triviality-compatible" approximations (in which the shifted "Higgs" field h(x)≡Φ(x)-<Φ> is governed by an effective quadratic Hamiltonian) predicts a phase transition that is very weakly first-order and that mh and v are both finite, cutoff-independent quantities. To test these two alternatives, we have numerically computed the effective potential on the lattice. Three different methods were used to determine the critical bare mass for the chosen bare coupling value. All give excellent agreement with the literature value. Two different methods for obtaining the effective potential were used, as a control on the results. Our lattice data are fitted very well by the predictions of the unconventional picture, but poorly by the conventional picture.

Nonconservation of the fermion number in the decay of a heavy fermion in a two-dimensional gauge model

1989 ◽  
Vol 78 (3) ◽  
pp. 284-291 ◽  
Author(s):  
G. G. Petriashvili
Keyword(s):  
Heavy Fermion ◽  
Two Dimensional ◽  
Gauge Model ◽  
Fermion Number

TIME DELAY IN SEMICLASSICAL SCATTERING THEORY

1995 ◽  
Vol 10 (33) ◽  
pp. 2509-2517
Author(s):  
M.P. PATO ◽  
M.S. HUSSEIN
Keyword(s):  
Time Delay ◽  
Effective Potential ◽  
Scattering Theory ◽  
Semiclassical Approximation ◽  
Asymptotic Series ◽  
Complex Potentials ◽  
Nuclear Scattering ◽  
Asymptotic Evaluation ◽  
Repulsive Potentials ◽  
Semiclassical Scattering

An asymptotic evaluation of the time delay in the context of the semiclassical approximation is performed. It is shown that it is related to Stokes’s discontinuities of the asymptotic series caused by singularities determined by the turning points and points of equilibrium of the effective potential in the complex r-plane. The theory is applied to the repulsive potentials inversely proportional to the fourth and the sixth power of the distance. The case of complex potentials, usually considered in nuclear scattering is also discussed.

scholarly journals ANOMALOUS FERMION MASS GENERATION AT THREE LOOPS

2013 ◽  
Vol 28 (22) ◽  
pp. 1350083 ◽  
Author(s):  
APOSTOLOS PILAFTSIS
Keyword(s):  
Gauge Theory ◽  
Quantum Gravity ◽  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Model Building ◽  
Heavy Fermions ◽  
Fermion Mass ◽  
Mass Generation ◽  
Fermion Masses ◽  
Gravity Effects

We present a novel mechanism for generating fermion masses through global anomalies at the three-loop level. In a gauge theory, global anomalies are triggered by the possible existence of scalar or pseudoscalar states and heavy fermions, whose masses may not necessarily result from spontaneous symmetry breaking. The implications of this mass-generating mechanism for model building are discussed, including the possibility of creating low-scale fermion masses by quantum gravity effects.

scholarly journals Effective potential (in)stability and lower bounds on the scalar (Higgs) mass

2005 ◽  
Vol 72 (6) ◽  
Author(s):  
Vincenzo Branchina ◽  
Hugo Faivre
Keyword(s):  
Lower Bounds ◽  
Effective Potential ◽  
Higgs Mass

Heavy-Fermion Mass Spectrum

1957 ◽  
Vol 107 (5) ◽  
pp. 1453-1454 ◽  
Author(s):  
D. Kleitman
Keyword(s):  
Mass Spectrum ◽  
Heavy Fermion ◽  
Fermion Mass

scholarly journals CURVATURE-INDUCED PHASE TRANSITION IN A FOUR-FERMION THEORY USING THE WEAK CURVATURE EXPANSION

1996 ◽  
Vol 11 (25) ◽  
pp. 4561-4576 ◽  
Author(s):  
TOMOHIRO INAGAKI
Keyword(s):  
Phase Transition ◽  
Chiral Symmetry ◽  
Effective Potential ◽  
Positive Curvature ◽  
Expansion Method ◽  
Space Time ◽  
Fermion Mass ◽  
De Sitter ◽  
Time Dimension ◽  
Arbitrary Space

Curvature–induced phase transition is thoroughly investigated in a four-fermion theory with N components of fermions for arbitrary space–time dimensions (2≤D<4). We adopt the 1/N expansion method and calculate the effective potential for a composite operator [Formula: see text]. The resulting effective potential is expanded asymptotically in terms of the space–time curvature R by using the Riemann normal coordinate. We assume that the space–time curves slowly, and we keep only terms independent of R and terms linear in R. In evaluating the effective potential it is found that first order phase transition is caused and the broken chiral symmetry is restored for a large positive curvature. In the space–time with a negative curvature the chiral symmetry is broken down even if the coupling constant of the four-fermion interaction is sufficiently small. We present the behavior of the dynamically generated fermion mass. The critical curvature, R cr , which divides the symmetric and asymmetric phases, is obtained analytically as a function of the space–time dimension D. At the four-dimensional limit our result R cr agrees with the exact results known in de Sitter space and the Einstein universe.

Sign in / Sign up

Export Citation Format

Share Document