Chemical equilibration of QGP enforcing baryon number conservation

Quark Gluon Plasma, likely to be created in high energy heavy ion collisions is sure to be in a state of both thermal and chemical non-equilibria. Once thermal equilibrium is attained, subsequently the system evolves according to the laws of hydrodynamics. As demanded by experimental results it is necessary to incorporate fermionic chemical potentials in the study of chemical equilibration. Moreover strong interaction conserves baryon number, which again must be incorporated into the scheme. The present work is aimed at attaining such an objective.     

Multiplicative conservation of baryon number and baryogenesis

In the canonical seesaw mechanism of neutrino mass, lepton number is only multiplicatively conserved, which enables the important phenomenon of leptogenesis to occur, as an attractive explanation of the present baryon asymmetry of the Universe. A parallel possibility, hitherto unrecognized, also holds for baryon number and baryogenesis. This new idea is shown to be naturally realized in the context of a known supersymmetric string-inspired extension of the Standard Model, based on E₆$E_6$ particle content, and having an extra UN₍₁₎$U{(1)}_N$ gauge symmetry. Within this framework, two-loop radiative neutrino masses are also possible, together with a new form of very long-lived matter.     

Reconstruction of baryon number distributions

The maximum entropy method(MEM) and Gaussian process(GP) regression,which are both wellsuited for the treatment of inverse problems,are used to reconstruct net-baryon number distributions based on a finite number of cumulants of the distribution.B ary on number distributions across the chiral phase transition are reconstructed.It is deduced that with the increase of the order of cumulants,distribution in the long tails,i.e.,far away from the central number,would become increasingly important.We ...     

Flavour equilibration studies of quark-gluon plasma with non-zero baryon density

Flavour equilibration for a thermally equilibrated but chemically non-equilibrated quark-gluon plasma is presented. Flavour equilibration is studied enforcing baryon number conservation. In addition to the usual processes like single additional gluon production gg ⇌ ggg and its reverse and quark-antiquark pair production by gluon pair fusion gg ⇌ q _i q _ı and reverse thereof, processes like quark-flavour interchanging q _i q _ı ⇌ q _j $ q_{\bar j} $ q_{\bar j} is also considered. The degree of equilibration is studied comparatively for various reactions/constraints that are being considered.     

Higher-order ratios of baryon number cumulants

The relevance of higher order cumulants of net baryon number fluctuations for the analysis of freeze-out and critical conditions in heavy-ion collisions at LHC and RHIC is addressed. The sign structure of the higher order cumulants in the vicinity of the chiral crossover temperature might be a sensitive probe and may allow to elucidate their relation to the QCD phase transition. We calculate ratios of generalized quarknumber susceptibilities to high orders in three flavor QCD-like models and investigate their sign structure close to the chiral crossover line.     

Elementary examples of baryon number generation

Elementary examples are provided of reaction rate matrices satisfying the constraints of unitarity and CPT invariance, which can lead a system with baryon number initially zero to evolve toward non-zero baryon number. The importance of the unitarity constraint is emphasized.     

Spontaneous breaking of global baryon number symmetry

We study the possibility that theU(1) _B global symmetry associated with baryon number is spontaneously broken. We present realistic examples implemented in the context of a suitably extended standardSU(2) _L×U(1)×SU(3)_c model and of a composite model of quarks and leptons. The globalU(1) _B symmetry in both cases is spontaneously broken at a relatively low mass scale without any conflict with observations. The dominant baryon number nonconserving process in these models obeys the ΔB=2 selection rule.     

Radiative corrections in monopole catalysis of baryon number violation

We propose an improved framework for discussing the monopole catalysis of proton decay. Instead of discarding higher partial waves from the outset we integrate over them and obtain the s-wave effective action. We present a detailed calculation to confirm that the effects of higher partial waves through one-loop radiative corrections neither spoil nor modify the conventional treatment of monopole catalysis of proton decay.     

On the distribution of baryon number in chiral bags

We calculate the even moments of the baryon number density originated from the vacuum polarization in chiral bags. All these moments are shown to be finite after the point splitting regularization. Our results agree very well with those derived from the parametrization of baryon density given by Jackson and Vepstas (accompanying article).     

Chemical equilibration of baryons in an expanding fireball

Due to long chemical equilibration times of hadrons in the hadron gas phase in relativistic heavy ion collisions it has been suggested that they are “born" into equilibrium. Here we review reactions that allow for quick equilibration times within the hadron gas phase such as multi-mesonic reactions at SpS and Hagedorn resonances decays at RHIC. The inclusion of a Bjorken expansion reveals that baryon anti-baryon pairs can quickly equilibrate within the hadron gas phase.     

Novel mechanisms of baryon number flow over large rapidity gap

It is shown that slow valence quark in the wave function of high energy proton can fragment into a baryon if the fast diquark-spectator is destroyed, i.e. is turned from the antitriplet to the sextet colour state. We estimated the cross section of the baryon number flow to the central rapidity region using the perturbative QCD. It depends on the rapidity gap Δy as exp (-Δy/2) and nicely agrees with the data at ISR energies, There exists also an intriguing possibility to transfer baryon number by means of gluonic exchanges only. This contribution does not depend on rapidity at all and becomes sizable in TeV energy region. We propose also new mechanisms for baryonantibaryon production from vacuum, transfer of polarization over large rapidity intervals, and nuclear stopping power.