Entropy, baryon asymmetry and dark matter from heavy neutrino decays

The origin of the hot phase of the early universe remains so far an unsolved puzzle. A viable option is entropy production through the decays of heavy Majorana neutrinos whose lifetimes determine the initial temperature. We show that baryogenesis and the production of dark matter are natural by-products of this mechanism. As is well known, the cosmological baryon asymmetry can be accounted for by leptogenesis for characteristic neutrino mass parameters. We find that thermal gravitino production then automatically yields the observed amount of dark matter, for the gravitino as the lightest superparticle and typical gluino masses. As an example, we consider the production of heavy Majorana neutrinos in the course of tachyonic preheating associated with spontaneous B−L breaking. A quantitative analysis leads to constraints on the superparticle masses in terms of neutrino masses: For a light neutrino mass of ¹⁰−5 eV the gravitino mass can be as small as 200 MeV, whereas a lower neutrino mass bound of 0.01 eV implies a lower bound of 9 GeV on the gravitino mass. The measurement of a light neutrino mass of 0.1 eV would rule out heavy neutrino decays as the origin of entropy, visible and dark matter.     

New constraints on “INO” masses from cosmology (I). Supersymmetric “inos”

In this first paper we derive new constraints on gravitino and photino masses in big bang cosmology. First, in the context of induced supersymmetry breaking we calculate explicitly the gravitino decay rate into gauginos, and find that in the absence of significant dilution the gravitino mass must be ?5 × 10⁴ GeV in order not to affect nucleosynthesis. We also find in this case that constraints in the lightest R-odd particle, the photino, differ significantly from earlier bounds based on analogy with stable heavy neutrino bounds in the standard model, due to out of equilibrium gravitino decay. In order to avoid both these constraints the gravitino distribution must be severely suppressed. If this is due to inflation, it must occur at a scale ?10¹⁰?10¹¹ GeV.     

Studying very light gravitino at the ILC

A collider signal with a stable gravitino of O(10) eV mass at the International Linear Collider (ILC) experiment is investigated. Such a light gravitino is generally predicted in the low-scale gauge mediation scenario of the supersymmetry breaking. We particularly focus on the case that the next lightest supersymmetric particle is stau, which eventually decays into a gravitino and a τ-lepton. With such a small gravitino mass, the lifetime of the stau is ¹⁰−15-¹⁰−11 s, and the produced stau decays before reaching the first layer of the inner detector of the ILC. It is shown, however, that the lifetime can be determined from the distribution of the impact parameter, which is obtained by observing charged tracks caused by decay products of the τ-lepton. This measurement also enables us to estimate the mass of the gravitino and determine the scale of the supersymmetry breaking. Based on a simulation study, we found that the lifetime can be measured when it is longer than ∼¹⁰−14 s and the stau mass is about 100 GeV.     

Associated production of light gravitinos in e+e? and e?γ collisions

Light gravitino productions in association with a neutralino (selectron) in e ⁺ e ⁻ (e ⁻ γ) collisions are restudied in a scenario that the lightest supersymmetric particle is a gravitino and the produced neutralino (selectron) promptly decays into a photon (electron) and a gravitino. We explicitly give the helicity amplitudes for the production processes by using the effective goldstino interaction Lagrangian, and present the cross sections with different collision energies and mass spectra. We also examine selection efficiencies by kinematical cuts and beam polarizations for the signal and background processes, and show that the energy and angular distributions of the photon (electron) can explore the mass of the t-channel exchange particle as well as the mass of the decaying particle at a future e ⁺ e ⁻ (e ⁻ γ) collider.     

Beta decay of <Superscript>115</Superscript>In to the first excited level of <Superscript>115</Superscript>Sn: Potential outcome for neutrino mass

Recent observation of β decay of ¹¹⁵In to the first excited level of ¹¹⁵Sn with an extremely low Q _β value (Q _β ≤ O(1) [keV]) could be used to set a limit on neutrino mass. To give a restriction potentially competitive with those extracted from experiments with ³H (≃2 eV) and ¹⁸⁷Re (≃15 eV), the atomic mass difference between ¹¹⁵In and ¹¹⁵Sn and energy of the first ¹¹⁵Sn level should be remeasured with higher accuracy (possibly of the order of ∼1 eV). The text was submitted by the authors in English.     

Supersymmetric relics from the big bang

We consider the cosmological constraints on supersymmetric theories with a new, stable particle. Circumstantial evidence points to a neutral gauge/Higgs fermion as the best candidate for this particle, and we derive bounds on the parameters in the lagrangian which govern its mass and couplings. One favored possibility is that the lightest neutral supersymmetric particle is predominantly a photino $\text{～}\text{γ}$ with mass above $\text{1}\text{2}$ GeV, while another is that the lightest neutral supersymmetric particle is a Higgs fermion with mass above 5 GeV or less than O(100) eV. We also point out that a gravitino mass of 10 to 100 GeV implies that the temperature after completion of an inflationary phase cannot be above 10¹⁴ GeV, and probably not above 3 × 10¹² GeV. This imposes constraints on mechanisms for generating the baryon number of the universe.     

Exact solution of the neutralino mass matrix

The eigenvalue problem for the neutralino mass matrix has been solved exactly and the eigenvalues are expressed in terms of thev ₁/v ₂, chargino and gluino masses which are directly measurable. An analytical formula for the lightest neutralino mass as a function of the above parameters is obtained. Formulae for the photino, zino and neutral higgsino contents of each of the physical neutralino mass eigenstates states have been found. Taking into account these formulae it has been possible to predict the upper (lower) bound on the mass of zino (photino) dominant neutralino states, including the lightest one. The neutralino-gluino and neutralino-chargino mass planes have also been constrained by using the latest LEP data.     

Constraints to the radiative lifetime of a light neutral fermion in the galactic halo from IUE

Summary We present the negative result of a search for the radiative decay of a light neutral fermion, that might be the neutrino (if massive) or the photino, gravitationally bounded to our Galaxy. The limit obtained for the radiative lifetime of a particle of mass between 12.5 and 21.5 eV is ≈10¹⁸ years. These new data on UV background in the range (1250÷2000) ? show the presence of continuum emission and diffuse lines emission at high galactic latitude (|b ^II|>45°). The lines are identifiable with C IV, λ-1549 ? and N III, λ=1749 ?. The continuum level sharply rises at 1680 ? to the level of (314±136) photons/(cm²s sr ?) and remains nearly constant up to 2000 Å. Below 1680 Å we found no emission with an upper limit of ≈100 units. These new data are briefly discussed in comparison with the results of previous experiments and theoretical expectations. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.     

Massive photinos and ultraviolet astronomy

The ionisation of hydrogen and helium in the intergalactic medium and of silicon and carbon in galactic halos, including our own, have already tentatively been attributed to photons emitted by decaying neutrinos created in the hot big bang. This hypothesis would require a neutrino mass ～ 100 eV and a radiative lifetime ～ 10²⁷ s. Here we point out that the same ideas could apply instead to photinos. If the photino mass is determined by the grand unification scale ～ 10¹⁵ GeV, then a mass ～ 100 eV would be compatible with experiment and the radiative lifetime of the photino would indeed be expected to be ～ 10²⁷ s.     

The cosmology of decaying gravitinos

We consider the cosmological constraints on unstable particles with masses O(m_W). Constraints from the energy density during primordial nucleosynthesis, from subsequent entropy generation, and from perturbations of the microwave background are not as restrictive as bounds from the dissociation of light elements. Most restrictive is the need to avoid over-production of D and ³He through the photo-dissociation of ⁴He. When applied to gravitinos, this bound imposes an upper limit of O(10⁸) GeV on the reheating temperature after inflation, which could create problems for baryosynthesis in supersymmetric theories. These problems can be avoided if the photino is heavier than the gravitino.     

Light gauginos: Masses and instabilities

Within the framework of supergravity models without grand unified steps, we analyse in detail the consequences of the hypothesis that gauginos have no bare masses due to supergravity interactions. To this purpose we have made a one-loop calculation of wino, zino, and photino masses and a renormalization group improved two-loop calculation of the gluino masses.We find that: (i) the non-observation of charged winos is compatible either with a gravitino mass m ? 300 GeV or $\text{m ?3}\text{TeV}$; (ii) with a top quark mark of about 40 GeV, gluino and photino have very similar masses ranging from O(1 GeV) to O(20 GeV). In most cases consistency with cosmology requires that the gauge singlet needed to break the SU(2) × U(1) symmetry, be the lightest stable supersymmetric particle, with a mass as low as 1 keV or less. In such cases photino (or gluino) lifetimes into one photon (gluon) and one light singlet fermion (zerino), are typically between 10^?3 and 1 sec.We discuss the problem of the experimental detection of gauginos, which, according to the various options, require rather different approaches.     

Experimental investigation of ligand effects on the conversion electron spectrum of the 22.5 keV M1 + E2 nuclear transition in <Superscript>149</Superscript>Sm

The conversion electron spectrum of the 22.5keV M1 + E2 nuclear transition in ¹⁴⁹Sm from the electron capture decay of ¹⁴⁹Eu was experimentally studied for the “Eu₂O₃” and “EuF₃” compounds in which ¹⁴⁹Eu ions have the same assumed oxidation number +3 . While the energies of the L, M, N, O, and P₁ conversion lines for “EuF₃” were lower, on average, by 1.7(1), 2.7(2), 2.3(3), 4.1(2), and 5.7(9)eV, respectively, than those for “Eu₂O₃”, no changes between the two ligand complexes were observed for relative intensities of the conversion lines and their natural widths within the error limits.     

Electrical properties of Cr-doped CoO

This paper reports the results of the electrical conductivity measurements for polycrystalline specimens of undoped and Cr-doped CoO in the ranges of p(O₂) (10⁻⁵ – 10⁵ Pa) and temperature (1223 – 1373 K). The experimental data are considered in terms of the effect of Cr on semiconducting properties of CoO. It is shown that Cr results in a decrease of the reciprocal of the p(O₂) exponent of electrical conductivity, however, the obtained experimental values are substantially lower than those predicted by defect chemistry. The activation energy of the electrical conductivity remains independent of p(O₂) and Cr content (at the level of about 0.5 eV) except strongly reduced CoO, at p(O₂)=2.10⁻⁴ Pa, of which the activation energy is substantially higher. Thermopowervs p(O₂) exhibits maximum at p(O₂)=10 Pa (except of thermopower data for Cr-doped CoO at the highest temperature). The experimental data are considered in terms of the effect of both p(O₂) and Cr on semiconducting properties.     

Constraints on light particles from stellar evolution

We examine the constraints imposed on the numbers and interactions of light particles by our understanding of the late stages of stellar evolution, including red giants, carbon-burning stars and cooling neutron stars. We show that these astrophysical considerations restrict the number of neutrino types to be less than 10^+2±1. This result complements the standard constraints from cosmological nucleosynthesis, which was unable to exclude numbers of neutrinos between a few thousand and the best particle physics limit of order 10⁵. We also investigate the constraints on supersymmetric theories with a light photino and gravitino, finding that the supersymmetry breaking scale parameter f>O(100GeV) and the selectron masses are >20 to 40 GeV. Finally, we study energy-loss rates by majoron and invisible axion emission.     

The neutralinos of theSU(N,1) minimal supergravity model and standard cosmology

We discuss the effect of the lightest supersymmetric particle (LSP), a Higgsino, and of the gravitino of theSU(N,1) minimal SUGRA model in the standard big bang theory. The freeze out of the LSP depends on the gravitino mass and on the top mass and leads to restrictive lower bounds for these parameters in the model. The decay of a gravitino with mass in the few TeV range leads to a delay in the cooling of the universe before nucleosynthesis. This constitutes the main bound on the gravitino mass of the model. The results are compared with the more standard “simultaneous decay approximation”.     

Comparative analysis of emission and absorption spectra of zinc oxide powders

Photoluminescence and optical absorption spectra induced by proton and electron irradiation in zinc oxide powders have been investigated. It has been found that the emission band in a visible region with a maximum of about 2.3 eV is a superposition of three bands with 2.55, 2.34, 2.12 eV, respectively, caused by oxygen vacancies V _O⁺, interstitial oxygen O _i ⁻, and zinc vacancies V _Zn⁻ absorbing in the 3.03-, 2.83-, and 2.64-eV bands.     

Electroweak precision data and gravitino dark matter

Electroweak precision measurements can provide indirect information about the possible scale of supersymmetry already at the present level of accuracy. We review present day sensitivities of precision data in mSUGRA-type models with the gravitino as the lightest supersymmetric particle (LSP). The χ ² fit is based on M _W , sin² θ _eff, (g−2) _μ , BR(b → sγ) and the lightest MSSM Higgs boson mass, M _h . We find indications for relatively light soft supersymmetry-breaking masses, offering good prospects for the LHC and the ILC, and in some cases also for the Tevatron.      

R-violating decay of Wino dark matter and electron/positron excesses in the PAMELA/Fermi experiments

We show that R-parity violating decay of Wino dark matter of mass about 3 TeV can naturally account for the flux and spectral shape of the cosmic-ray electrons and positrons observed by the PAMELA and Fermi satellites. To provide a theoretical basis for the scenario, we present a model in which trilinear R-parity breaking appears with a coefficient suppressed by powers of the gravitino mass, which naturally leads to the Wino lifetime of O(10²⁶) seconds.     

Measuring neutrino mass with radioactive ions in a storage ring

We propose a method to measure the neutrino mass kinematically using beams of ions which undergo beta decay. The idea is to tune the ion beam momentum so that in most decays, the electron is forward moving with respect to the beam, and only in decays near the endpoint is the electron moving backwards. Then, by counting the backward moving electrons one can observe the effect of neutrino mass on the beta spectrum close to the endpoint. In order to reach sensitivities for m _ν <0.2 eV, it is necessary to control the ion momentum with a precision better than δ p/p<10⁻⁵, identify suitable nuclei with low Q-values (in the few to ten keV range), and one must be able to observe at least O(10¹⁸)\mathcal{O}(10^{18}) decays.     

Weak interactions of a light gravitino: A lower limit on the gravitino mass from the decay ψ→gravitino + antiphotino

The massive gravitino of spontaneously-broken locally supersymmetric theories may well be very light, leading to a mixing between weak and gravitational interactions. Particularly interesting is the photon coupling to a gravitino-antiphotino pair, with a vertex factor ($\text{κ/m}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext><mtext>\surd 6</mtext>}}\text{) γ}{}^{\mathrm{\mu }}\text{q}{}^2$: a one-photon exchange with ordinary fermions is equivalent to a local four-fermion interaction. From the upper limit on the decay ψ → gravitino + antiphotino we get a lower limit ～ 10^?8 eV/c² on the gravitino mass.