Gary Steigman

Primordial nucleosynthesis: A critical comparison of theory and observation

Primordial nucleosynthesis is reexamined in the context of a detailed comparison of theory and observation. A new argument is presented to show how the observed abundances of D and /sup 3/He can be used to derive a lower bound to the nucleon density. In concert with the previously known upper bound from D alone, we define a conservative (safe bet) range for the nucleon-to-photon ratio: eta = (3-10) x 10/sup -10/. New observations of /sup 7/Li are consistent with the abundances of D and /sup 3/He and help us sto define a reasonable (best bet) range: eta = (4-7) x 10/sup -10/. In either of these ranges the predicted and observed abundances of D, /sup 3/He, and /sup 7/Li re all in concordance. The upper bounds correspond to ..cap omega../sub N/ or =0.24 if N/sub v/> or =3 and tau/sub 1/2/> or =10.4 minutes.«xa0less

Cosmological Limits to the Number of Massive Leptons

Abstract If massive leptons exist, their associated neutrinos would have been copiously produced in the early stages of the hot, big bang cosmology. These neutrinos would have contributed to the total energy density and would have had the effect of speeding up the expansion of the universe. The effect of the speed-up on primordial nucleosynthesis is to produce a higher abundance of 4 He. It is shown that observational limits to the primordial abundance of 4 He lead to the constraint that the total number of types of heavy lepton must be less than or equal to 5.

Some Astrophysical Consequences of the Existence of a Heavy Stable Neutral Lepton

Recently, high-energy particle theorists have constructed new extended gauge theories which may fit experiment somewhat better than previous already very successful theories. One of the predictions which is often discussed is the possible existence of a stable neutral lepton, probably with a mass of a few GeV/c/sup 2/. Following this motivation we here investigate some cosmological consequences of the existence of any stable, massive, neutral lepton, and show that it could well dominate the present mass density in the universe. The contribution to the mass density depends on the mass of the lepton, which should eventually be determined with high-energy accelerators. It is interesting that the more massive the lepton, the smaller its contribution to the present mass density. It is unlikely that these leptons affect big bang nucleosynthesis or condense into stellar size objects. However, such a lepton is an excellent candidate for the material in galactic halos and for the mass required to bind the great clusters of galaxies. Annihilation radiation from these structures should be detectable. At the end of the paper a brief mention is made of the astrophysical constraints on the mass-lifetime relationship if the neutral lepton is unstable.

Cosmological constraints on the properties of weakly interacting massive particles

Considerations of the age and density of, as well as the evolution of structure in, the universe lead to constraints on the masses and lifetimes of weakly interacting massive particles (WIMPs). The requirement that the observed large-scale structure of the universe be permitted to develop, leads to much more restrictive bounds on the properties of WIMPs than those which follow from considerations of the age and density of the universe alone.

Implications of the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism of amplification of neutrino oscillations in matter

Abstract Mikheyev and Smirnov have recently proposed a novel and plausible solution of the solar neutrino problem, based on the resonant amplification of the neutrino oscillations in matter. We comment on several aspects of this mechanism. (i) For the values of neutrino masses and mixing angles predicted by the seesaw model of grand unified theories, the MSW effect may take place naturally in the Sun, leading to a considerable reduction of the flux of solar electron neutrinos, with the dominant transition being v e → v τ (rather than v e → v μ ). (ii) Oscillations between the ordinary neutrinos ( v e , v μ , v τ ) can affect primordial nucleosynthesis, but the effect is small (i.e., the abundance of 4 He is predicted to change by less than 1.3 × 10 −3 ). (iii) A comparison of some of the general properties of neutrino oscillations in matter and in vacuum is given.

Big-bang nucleosynthesis revisited

Abstract We compute the homogeneous big-bang nucleosynthesis yields of D, 3 He, 4 He, and 7 Li, taking into account recent measurements of the neutron mean-life as well as updates of several nuclear reactions rates which primarily affect the production of 7 Li. We discuss the extraction of primordial abundances from observation and the likelihood that the primordial mass fraction of 4 He, Y p , is less than or equal to 0.24. Using the primordial abundances of D+ 3 He and 7 Li we limit the baryon-to-photon ratio ( η in units of 10 −10 ): 2.6 ⩽ η 10 ⩽ 4.3 (or, in terms of the present mass density in baryons, 1.8×10 −31 ⩽ ϱ B ⩽ 3.0×10 −31 g/cm 3 , for a microwave background temperature of 2.75°) which we use to argue that baryons contribute between 0.02 and 0.11 to the critical energy density of the universe. An upper limit to Y p of 0.24 constrains the number of light neutrinos to N ν ⩽ 3.4, in excellent agreement with the LEP and SLC collider results. We turn this argument around to show that the collider limit of 3 neutrino species can be used to bound the primordial abundance of 4 He: 0.235 ⩽ Y p ⩽ 0.245.

Limits on New Superweakly Interacting Particles from Primordial Nucleosynthesis

The existence of massless (or low mass) weakly (or superweakly) interacting particles is predicted by various models of unified theories. Such particles (neutrinos, gravitinos, gravitons) would contribute to the early expansion rate of the universe and affect the outcome of primordial nucleosynthesis. We extend previous work on the limits to the number of “ordinary” neutrinos to more weakly interacting particles which decouple earlier in the evolution of the universe. We have evaluated the limits on the number of “new” particles permitted as a function of their interaction strength. Having been forced to consider the universe at earlier times and higher temperatures than was necessary in previous discussions we have dealt, qualitatively, with the transition from free quarks to confined hadrons. We find that the maximum number of superweakly interacting, light (< 1 MeV) particles is between ∼1 and ∼20, depending on the strength of their interaction. These constraints may serve as a useful guide for new unification theories.

Relic Neutrinos and the Density of the Universe

Relic neutrinos will be abundant today (n/sub v/roughly-equaln/sub y/) and could, if they have a small mass (m/sub v/> or approx. =1.4 eV), dominate the universal mass density. Ordinary matter (nucleons) appears to be incapable of accounting for the dynamically inferred mass on scales of clusters of galaxies; recent indications suggest that this problem may persist down to the scale of binary galaxies and small groups of galaxies. The difficulty is that, were the mass on these scales in nucleons, too much helium and too little deuterium would have been produced during primordial nucleosynthesis. Light neutrions with m/sub v/ or approx. =1 eV. Heavy neutrinos with m/sub v/> or approx. =20 eV could be collapsed along with galaxies and, unless there were a subsequent segregation of nucleonic matter from neutrinos, would contribute too much invisible mass on such scales. Relic neutrinos with 4< or approx. =m/sub v/< or approx. =20 eV could supply most of the unseen mass on scales ranging from binaries through small groups to large clusters. Such neutrinos will dominate the mass of the universe and,morexa0» along the ordinary nucleons, could come close to closing the universe without violating the nucleosynthesis constraints.«xa0less

A reexamination of the cosmological bound to the number of neutrino flavors

Abstract The predictions of the light element abundances produced primordially in the standard hot big bang cosmological model with three species of light neutrinos ( N ν =3) is consistent with current observational data. If additional species of light neutrinos exist, additional 4 He is produced primordially; consistency with observations of 4 He leads to an upper bound to N ν which depends on the neutron half-life ( τ 1 2 ), the nucleon-to-photon ratio (or, equivalently, the primordial abundances of deuterium and helium-3) and the primordial mass fraction of 4 He ( Y p ). The bounds to these quantities are reexamined and N ν ⩽4.0 is reconfirmed.

Exotic relics from the big bang

Abstract New, exotic (very heavy and/or very weakly interacting) particles would have been produced in the hot, dense environment of the early Universe. If sufficiently long-lived, some exotic relics would have survived to influence the subsequent evolution of the Universe; some may be present today. The laboratory and astrophysical information which can constrain the properties of such new particles is outlined and guidelines are presented for testing models of elementary particle physics.