Searcharxiv⌕ Search

arXiv subjects

T. Moroi

Publications and source records attributed to T. Moroi.

At least 19 recordsLinked to original sources
arXiv1997

Exact Event Rates of Lepton Flavor Violating Processes in Supersymmetric SU(5) Model

Event rates of various lepton flavor violating processes in the minimal supersymmetric SU(5) model are calculated, using exact formulas which include Yukawa vertices of lepton-slepton-Higgsino. We find subtlety in evaluating event rates due to partial cancellation between diagrams. This cancellation typically reduces the event rates significantly, and the size of the reduction strongly depends on superparticle mass spectrum.

hep-ph↗
arXiv1996

Report of the Supersymmetry Theory Working Group

We provide a mini-guide to some of the possible manifestations of weak scale supersymmetry. For each of six scenarios we provide a brief description of the theoretical underpinnings, the adjustable parameters, a qualitative description of the associated phenomenology at future colliders, comments on how to simulate each scenario with existing event generators.

hep-ph↗
arXiv1996

Will at least one of the Higgs bosons of the next-to-minimal supersymmetric extension of the Standard Model be observable at LEP2 or the LHC?

We demonstrate that there are regions of parameter space in the next-to-minimal (i.e. two-Higgs-doublet, one-Higgs-singlet superfield) supersymmetric extension of the SM for which none of the Higgs bosons are observable either at LEP2 with $\sqrt{s}=192 GeV$ and an integrated luminosity of $L=1000 inverse pb$ or at the LHC with $L=600 inverse fb$.

hep-ph↗
arXiv1995

Can Decaying Particles Raise the Upperbound on the Peccei-Quinn Scale?

We have reexamine the effect of entropy production on the cosmic axion density and find that the Peccei-Quinn scale $F_a$ larger than about $10^{15}$~GeV is not allowed even if large entropy is produced by the decays of coherent oscillations or non-relativistic massive particles. We stress that this result is independent of the details of models for the decaying particles.

hep-ph↗
arXiv1995

On the Solution to the Polonyi Problem with No-Scale Type Supergravity

We study the solution to the Polonyi problem in the framework of no-scale type supergravity. In such a model, Polonyi field can weigh as $O(10{\rm TeV})$ and decay just before the big-bang nucleosynthesis. It is shown that in spite of a large entropy production by the decay of the Polonyi field, one can naturally explain the present value of the baryon-to-entropy ratio, $n_B/s \sim (10^{-10}-10^{-11})$ if the Affleck-Dine mechanism for baryogenesis works. It is pointed out, however, that there is another cosmological problem related to the abundance of the lightest superparticles produced by the decay of the Polonyi field.

hep-ph↗
arXiv1995

Lepton-Flavor Violation via Right-Handed Neutrino Yukawa Couplings in Supersymmetric Standard Model

Various lepton-flavor violating (LFV) processes in the supersymmetric standard model with right-handed neutrino supermultiplets are investigated in detail. It is shown that large LFV rates are obtained when $\tan β$ is large. In the case where the mixing matrix in the lepton sector has a similar structure as the Kobayashi-Maskawa matrix and the third-generation Yukawa coupling is as large as that of the top quark, the branching ratios can be as large as $Br(μ\rightarrow eγ)\simeq 10^{-11}$ and $Br(τ\rightarrowμγ)\simeq 10^{-7}$, which are within the reach of future experiments. If we assume a large mixing angle solution to the atmospheric neutrino problem, rate for the process $τ\rightarrowμγ$ becomes larger. We also discuss the difference between our case and the case of the minimal $SU(5)$ grand unified theory.

hep-ph↗
arXiv1995

Constraint on the Reheating Temperature from the Decay of the Polonyi Field

We study the Polonyi problem in the framework of no-scale type supergravity models. We show that the lightest superparticle (LSP) produced in the decay of the Polonyi field may contribute too much to the present density of the universe. By requiring that LSP should not overclose the universe, we obtain a stringent constraint on the reheating temperature after the decay of the Polonyi field. We calculate the LSP density with physical parameters obtained by solving renormalization group equations in the minimal supersymmetric SU(5) model and find that the reheating temperature should be greater than about 100MeV which corresponds to $O$(100)TeV of the Polonyi mass.

hep-ph↗
arXiv1995

Search for Dynamical Symmetry Breaking Physics by Using Top Quark

We report first results from the investigation on probing dynamical mechanism of the electroweak symmetry breaking using top quark. We consider the case where the top mass originates from a fermion-antifermion pair condensate, which necessitates (i)strong interaction to cause condensation, and (ii)4-fermi interaction to give top mass. From the observed top mass and the unitarity constraint, we obtain, for the 4-fermi interaction (ii), lower bounds for its strength and upper bounds for its intrinsic new mass scale as we vary the type of the strong interaction (i). Bethe-Salpeter and Schwinger-Dyson equations are solved numerically to study the dynamical symmetry breaking effect semi-quantitatively.

hep-ph↗
arXiv1995

Gravitino Production in the Inflationary Universe and the Effects on Big-Bang Nucleosynthesis

Gravitino production and decay in the inflationary universe are reexamined. Assuming that the gravitino mainly decays into a photon and a photino, we calculate the upperbound on the reheating temperature. Compared to previous works, we have essentially improved the following two points: (i) the helicity $\pm\frac{3}{2}$ gravitino production cross sections are calculated by using the full relevant terms in the supergravity lagrangian, and (ii) the high energy photon spectrum is obtained by solving the Boltzmann equations numerically. Photo-dissociation of the light elements (D, T, $^3$He, $^4$He) leads to the most stringent upperbound on the reheating temperature, which is given by ($10^{6}$--$10^{9}$)GeV for the gravitino mass 100GeV--1TeV. On the other hand, requiring that the present mass density of photino should be smaller than the critical density, we find that the reheating temperature have to be smaller than ($10^{11}$--$10^{12}$)GeV for the photino mass (10--100)GeV, irrespectively of the gravitino mass. The effect of other decay channels is also considered.

hep-ph↗
arXiv1994

Electromagnetic Cascade in the Early Universe and its Application to the Big-Bang Nucleosynthesis

We investigate the electromagnetic cascade initiated by injection of very high energy photons in the early Universe and calculate the cascade spectrum by solving a set of Boltzmann equations numerically. In the calculation we take account of Compton scattering off the background electrons and pair creation off the background nucleons as well as photon-photon processes and inverse Compton scattering. We also apply our cascade spectrum to the big bang nucleosynthesis with photo-dissociation processes due to heavy unstable particles and obtain the constraint on their lifetime and abundance.

astro-ph↗
arXiv1994

Limit on the Color-Triplet Higgs Mass in the Minimum Supersymmetric SU(5) Model

In the minimum supersymmetric SU(5) GUT, we derive the upper limit on the mass of the color-triplet Higgs multiplets as $\mhc\leq 2.4\times 10^{16}~\GEV$ (90 \% C.L.) taking all possible corrections into account in a renormalization group analysis. If the above upper limit is compared with a limit on $\mhc$ from the negative search for the proton decay; $\mhc \geq 2.0\times 10^{16}~\GEV$ (in which effects of the larger top-quark mass are included), the minimum supersymmetric SU(5) GUT is severely constrained.

hep-ph↗
arXiv1994

On the Solution to the Polonyi Problem with $O$(10~TeV) Gravitino Mass in Supergravity

We study the solution to the Polonyi problem where the Polonyi field weighs as $O(10{\rm TeV})$ and decays just before the primordial nucleosynthesis. It is shown that in spite of a large entropy production by the Polonyi field decay, one can naturally explain the present value of the baryon-to-entropy ratio, $n_B/s \sim (10^{-10}-10^{-11})$ if the Affleck-Dine mechanism for baryogenesis works. It is pointed out, however, that there is another cosmological problem related to the abundance of the lightest superparticles produced by the Polonyi decay.

hep-ph↗
arXiv1994

Gravitino Decay into a Neutrino and a Sneutrino in the Inflationary Universe

Gravitino produced in the inflationary universe are studied. When the gravitino decays into a neutrino and a sneutrino, the emitted high energy neutrinos scatter off the background neutrinos and produce charged leptons (mainly electrons and positrons), which cause the electro-magnetic cascades and produce many soft photons. We obtain the spectra of the high energy neutrinos as well as the spectrum of the high energy photon by integrating a set of Boltzmann equations. Requiring these photons should not alter the abundances of the light elements (D, $^3$He, $^4$He) in the universe, we can set the stringent upperbound on the reheating temperature after the inflation. We find that $T_R \lesssim (10^{10}-10^{12})$GeV for $m_{3/2}\sim (100\GEV - 1\TEV)$, which is more stringent than the constraints in the previous works.

hep-ph↗
arXiv1994

Suppression of Proton Decay in the Missing-Partner Model for Supersymmetric SU(5) GUT

We construct a missing-partner model for supersymmetric SU(5) GUT assuming the Peccei-Quinn symmetry, in which the SU(5) gauge coupling constant remains in the perturbative regime below the gravitational scale $\sim2.4\times 10^{18}\GEV$. The Peccei-Quinn symmetry suppresses the dangerous dimension-five operators for the nucleon decay much below the limit from the present proton-decay experiments. We also stress that due to this suppression mechanism our model can accommodate even the large $\tanβ_H$ ($\sim$ 60) scenario which has been recently suggested to explain the observed value of the $m_b/m_τ$ ratio.

hep-ph↗
arXiv1994

Flat Potential for Inflaton with a Discrete $R$-invariance in Supergravity

We show that a very flat potential of inflaton required for a sufficient inflation is naturally obtained in $N=1$ supergravity by imposing a discrete $R$-invariance $Z_{n}$. Several cosmological constraints on parameters in the inflaton superpotential are derived. The reheating temperature turns out to be $(1-10^8)$GeV for the cases of $n$=3--10. Baryogenesis in this model is also discussed briefly.

hep-ph↗
arXiv1994

Gravitino Production in the Inflationary Universe and the Effects on Big-Bang Nucleosynthesis

Gravitino production and decay in the inflationary universe are reexanimed. Assuming that gravitino mainly decays into photon and photino, we have calculated the upperbound of the reheating temperature. Compared to previous works, we have essentially improved the following two points; (i) the helicity $\pm\frac{3}{2}$ gravitino production cross sections are calculated by using the full relevant terms in the supergravity lagrangian, and (ii) high energy photon spectrum is obtained by solving the Boltzmann equations numerically. Photo-dissociation of the light elements (D, T, $^3$He, $^4$He) leads to the most stringent upperbound of the reheating temperature, which is given by ($10^{6}$--$10^{9}$)GeV for the gravitino mass 100GeV--1TeV. On the other hand, requiring that the present mass density of photino should be smaller than the critical density, we find that the reheating temperature have to be smaller than ($10^{11}$--$10^{12}$)GeV for the photino mass (10--100)GeV, irrespectively of the gravitino mass. The effect of other decay channel is also considered.

astro-ph↗