Rahim Esmailzadeh

Is the Universe Closed by Baryons? Nucleosynthesis With a Late Decaying Massive Particle

A late decaying (7 > 105sec), massive (M 2 10 GeV) particle initiates a new phase of nucleosynthesis in the keV era. Light element production takes place when the hadronic decay products interact with the amb ient protons and ’ 4 He causing hadronic showers and 4 He hadrodestruction. The primordial abundances of D, 3He, 6Li and ‘Li-are given by the fixed points of the corresponding rate equations in which hadroproduct ion balances photodestruction. Since fixed points erase all previous memory, the primordial abundances of these elements are completely independent of the physics before the keV era, whose only important role is to provide at least the observed abundance of 4He. Any overabundance of 4He is subsequently hadrodissociated. The primordial element abundances are inagreement with observations; furthermore they are independent of RBhz . . . for a very broad range of ClBhz which includes the previously forbidden range 0.03 -5 flBhz 5 1.1. An ideal candidate for the late decaying particle may be the gravitino. --

Limits on late decaying particles from nucleosynthesis

Late decaying (τ > 104 s) particles can alter the standard big bang predictions for the light-element abundances. If M > 10 GeV, light-element production and 4He destruction can take place when hadronic decay products interact with the ambient protons and 4He causing hadronic showers; pepletion is the result of photodissociation by energetic decay protons. Previous works [1–4] which put limits in the properties of these particles ignored hadronic showers entirely, and usually considered only selected photodissociation reactions. We consider the full set of reactions and present both analytic and numerical bounds on the properties of particles with lifetimes greater than 104 s. This drastically alters the limits on particle masses, lifetimes and abundances. For a gravitino lighter than a TeV, the reheat temperature must be less than 1010 GeV.

Primordial nucleosynthesis without a computer

Approximate results for the standard theory of big bang nucleosynthesis are derived analytically, i.e., without the use of the Wagoner code, using ideas of fixed points and freezeout. The element abundances follow quasi-static equilibrium and eventually freeze out near their final values. The calculations are relatively simple and provide a better understanding of the physics than is possible from a numerical code containing nearly 100 reactions. 12 refs.

TeV Dark Matter

Abstract The minimal standard model has no candidates for non-baryonic dark matter of the universe. We add a single SU(3)×SU(2)×U(1) fermionic multiplet to this model and compute the mass necessary for it to close the universe as a function of its gauge quantum numbers. The simplest dark matter candidate, not already excluded by existing dark matter searches, is the neutral component of a zero hypercharge Dirac triplet. It couples to nuclei via two-W exchange, with an effective coupling three orders of magnitude smaller than ordinary weak interactions. Its charged partners are a few hundred MeV heavier and can be produced at SSC or LHC.

Electroweak phase transition and dark matter abundance

Abstract If the critical temperature of the electroweak phase transition is sufficiently small, it can change the final abundances of heavy dark matter particles, by keeping them massless for a long time. Recent experimental bounds on the Higgs mass from LEP imply that this is not the case in the minimal standard model.