Thermodynamic generation of the baryon asymmetry

A new technique for generating the baryon asymmetry of the universe is discussed. By using the natural CPT non-invariance of the universe during its early history, we discuss how a baryon asymmetry can develop while baryon violating interactions are still in thermal equilibrium with respect to an effective hamiltonian. Furthermore, both the ground state and fundamental interactions in these theories can be CP conserving.     

Spontaneous baryogenesis

The recently discovered mechanism of “spontaneous baryogenesis” for generating the baryon asymmetry is implemented in several particle physics models. In these scenarios, baryon number is an approximate symmetry spontaneously broken at a scale |;. The baryon asymmetry is generated without CP violation. Furthermore, this can come about during an epoch when baryon violation is in thermal equilibrium. We consider how various observational constraints affect the realization of this mechanism in acceptable models of particle interactions, and find that the observed baryon asymmetry can be produced for |;≳ 3 × 10¹³ GeV.     

Electroweak baryon number violation at finite temperature

We consider baryon and lepton number violating processes in the electroweak theory induced by gauge and Higgs fields passing the sphaleron solution at finite temperature. We show that for temperatures larger than 19 GeV the anomalous baryon and lepton number violating processes are suppressed by the Boltzmann factor exp (?βE _sp), whereE _sp is the sphaleron energy, rather than by the instanton tunneling factor exp (?8π²/g ²). We caculate the rate of baryon and lepton number violating processes at finite temperature and determine the freezing temperature of the anomalous processes in the early universe as a function of the Higgs mass. We compare the freezing temperature with the critical temperature of the electroweak phase transition infered from the one-loop finite-temperature effective potential. We obtain a critical Higgs mass of the order of 100 GeV, slightly depending on the top mass and the magnitude of the pre-exponential factor in the rate of theB non-conservation, above which the anomalous processes are certainly in equilibrium after the electroweak phase transition. Assuming that the temperature-dependence of the sphaleron energy is given by that found from the one-loop finitetemperature effective potential, this critical Higgs mass is lowered to a value of the order of 50 GeV.     

Proton Decay in Grand Unified Theories

Interactions which violate the conservation of baryon and lepton number represent an intrinsic part of all grand unified theories (GUTs) of strong and electroweak interactions. These new interactions — predicted within the framework of GUTs — generate B and L violating four-fermion interactions via the exchange of superheavy particles which cannot be ascribed a well-defined baryon or lepton number. The effective coupling constant of these four-fermion interactions might be large enough to make the proton decay detectable by the present generation of experiments. In this review the basic concepts of conventional as well as supersymmetric GUTs relevant for proton decay are sketched. The baryon number violating sector of grand unified theories is discussed in more detail. Special emphasis is laid on the various selection rules arising as consequences of low-energy gauge invariance and supersymmetry for proton decay. These selection rules already determine the coarse pattern of the resulting decay modes and branching ratios without any reference to or detailed knowledge of the underlying grand unified theory. Finally the numerous theoretical predictions are summarized and confronted with experiment.     

Gravitational leptogenesis in teleparallel and symmetric teleparallel gravities

In this study, we investigate the possibilities of generating baryon number asymmetry under thermal equilibrium within the frameworks of teleparallel and symmetric teleparallel gravities. Through the derivative couplings of the torsion scalar and the non-metricity scalar to baryons, baryon number asymmetry is produced in the radiation dominated epoch. For gravitational baryogenesis mechanisms in these two frameworks, the produced baryon-to-entropy ratio is too small to be consistent with observations. However, the gravitational leptogenesis models within both frameworks have the potential to explain the observed baryon-antibaryon asymmetry.     

Monte Carlo simulation of baryon and lepton number violating processes at high energies

We report results obtained with the first complete event generator for electroweak baryon and lepton number violating interactions at supercolliders. Typical events contain of the order of 50 electroweak gauge bosons, some Higgs bosons and quarks and leptons of all generations. There is still great uncertainty about the expected rate, but an event generator is needed in any case to establish what experimental limits can be placed on the cross section, and to determine whether, even if such spectacular events are seen, baryon and/or lepton number violation can be conclusively demonstrated. We find that baryon number violation would be very difficult to establish, but lepton number violation can be seen provided at least a few hundredL violating events are available with good electron or muon identification in the energy range 10 GeV to 1 TeV. The event generator, which takes the form of a package (HERBVI) interfacing to the existing simulation program HERWIG, should be useful for the coming period of detailed experiment design for the Large Hadron Collider (LHC) at CERN.     

宇宙中的光子数、重子数、及反重子数

在粒子物理与宇宙学二者的结合上,近年已经取得了颇有意义的进展。重子不对称和重子光子数比的起源可以用大统一理论加以解释。由B、C及CP破坏的相互作用可以说明为什么初始重子对称的宇宙能演化成不对称的。目前观测到的重子光子数比10~(-9)可能是由极早期宇宙中的超重玻色子的衰变产生的,在这种衰变中C及CP是破坏的。尽管衰变解释是吸引入的,但它的具体预言很强地依赖于超重玻色子的质量,以致其数值尚不确定。因此。为了进一步考查衰变模型的合理性,至少还要研究其他的可能有影响的过程。在这个意义下,本文还讨论了宇宙早期中的Higgs相变对重子光子比的影响。     

Cosmological implications of observable neutron-antineutron oscillations

A wide class of gauge theoretical models allowing for observable neutron-antineutron oscillations predict no baryon asymmetry in the present universe. This is to be traced back to the existence of baryon-violating interactions in equilibrium at the characteristic mass scale of neutron-antineutron oscillations. Then, we show how these models can be modified in such a way that a very late cosmological baryon asymmetry survives in the today universe. Specifically, we consider two recently proposed baryon-production mechanisms, one of which can be naturally embedded in a grand unification scheme and can lead to observable nucleon decay processes occurring only throughB-L violating butB+L conserving channels.     

Comments on the possibility of electroweak baryon number violation at high temperatures

Anomalous baryon number violation in the standard electroweak theory was first discussed by 't Hooft, who found it to be suppressed by a large factor exp(−8π²/g²) at zero temperature, due to a large energy barrier separating vacua with different baryon number. One might have expected that in the early Universe or in high-energy collisions, this process would become unsuppressed when the energies involved became comparable to the barrier height. We argue here that in both cases processes violating baryon number are likely to remain suppressed by a least the same zero-temperature factor.     

Baryon number violating nuclear decay

The expressions for baryon number violating nuclear partial decay widths are derived from the interactions as predicted by grand unified theories. Theory predicts that the baryon number violating proton decay inside the nucleus is hindered relative to the free proton decay rate. In the case of closed shell nuclei, the meson spin-isospin dependence of the partial width is the same as that for the nucleon decay. The branching ratios of decay amplitudes depend on the nuclear binding energies. Nuclear structure introduces lepton energy spread of ±49.5 MeV for light closed shell nuclei, while it does not affect the back to back emission of lepton-meson pair.     

Effect of pre-existing baryon inhomogeneities on the dynamics of quark-hadron transition

Baryon number inhomogeneities may be generated during the epoch when the baryon asymmetry of the universe is produced, e.g. at the electroweak phase transition. These lumps will have a lower temperature than the background. Also the value ofT _c will be different in these regions. Since a first-order quark-hadron (Q–H) transition is susceptible to small changes in temperature, we investigate the effect of the presence of such baryonic lumps on the dynamics of the Q–H transition. We find that the phase transition is delayed in these lumps for significant overdensities. Consequently, we argue that baryon concentration in these regions grows by the end of the transition. We mention some models which may give rise to such high baryon overdensities before the Q–H transition.     

Baryon asymmetry generation through preonic monopoles

A scheme is presented for baryon asymmetry generation in early universe through monpole-induced baryon number violating processes in the context of a preonic model.     

The development of baryon asymmetry in the early universe

The development of an excess of baryons over antibaryons due to CP and baryon number violating reactions during the very early stages of the big bang is calculated in simple models using the Boltzmann equation. We show that it is necessary to solve the coupled Boltzmann equations in order to determine the final baryon number in any specific model.     

Single field baryogenesis

We propose a new variant of the Affleck-Dine baryogenesis mechanism in which a rolling scalar field couples directly to left- and right-handed neutrinos, generating a Dirac mass term through neutrino Yukawa interactions. In this setup, there are no explicitly CP violating couplings in the Lagrangian. The rolling scalar field is also taken to be uncharged under the B - L quantum numbers. During the phase of rolling, scalar field decays generate a nonvanishing number density of left-handed neutrinos, which then induce a net baryon number density via electroweak sphaleron transitions.     

Baryon asymmetry, inflation and squeezed states

We use the general formalism of squeezed rotated states to calculate baryon asymmetry in the wake of inflation through parametric amplification. We base our analysis on a B and CP violating Lagrangian in an isotropically expanding universe. The B and CP violating terms originate from the coupling of complex fields with non-zero baryon number to a complex background inflaton field. We show that a differential amplification of particle and antiparticle modes gives rise to baryon asymmetry.     

Rate of anomalous electroweak baryon and lepton number violation at finite temperature

Using Langer's statistical theory of the decay of metastable states we calculate the rate of the anomalous electroweak baryon and lepton number violating processes in the case that the electroweak phase transition is of second order. Our formulas are valid in a temperature range between M_w and the critical temperature T_c. We get a dissipation of the baryon and lepton number of the order of exp(4.6×10⁹).     

Observing B-violation in relativistic heavy-ion collisions

Under certain situations, partons formed in heavy-ion collision experiments may expand out forming a shell-like structure. The partons in the outer shell subsequently hadronize, leaving a bubble of pure deconfined vacuum for a first-order quark-hadron phase transition. The bubble collapses and may eventually decay into particles which may thermalize to temperatures exceeding the electroweak transition temperature (100 GeV) at LHC. This will lead to the possibility of unsuppressed electroweak baryon number violating processes.     

Electroweak sphalerons with spin and charge

We show that, at finite weak mixing angle the sphaleron solution of Weinberg–Salam theory can be endowed with angular momentum proportional to the electric charge. Carrying baryon number 1/2 these sphalerons with spin and charge may contribute to baryon number violating processes.     

Leptogenesis from spin-gravity coupling following inflation

The energy levels of the left- and the right-handed neutrinos are split in the background of gravitational waves generated during inflation, which, in presence of lepton-number-violating interactions, gives rise to a net lepton asymmetry at equilibrium. Lepton number violation is achieved by the same dimension five operator which gives rise to neutrino masses after electroweak symmetry breaking. A net baryon asymmetry of the same magnitude can be generated from this lepton asymmetry by electroweak sphaleron processes.     

Nonequilibrium in the very early universe

It is argued that the small horizon when the universe was close to the Planck temperature restricted the possible energies of elementary particles, preventing them from being in full thermal equilibrium. Grand unified particle interactions seem unlikely to have thermalized the universe much before the temperature fell to the mass scale of the baryon-number violating bosons.