arXiv subjects

Takeo Moroi

Publications and source records attributed to Takeo Moroi.

At least 163 records · Page 9Linked to original sources

arXiv2002

Cosmic Density Perturbations from Late-Decaying Scalar Condensations

We study the cosmic density perturbations induced from fluctuation of the amplitude of late-decaying scalar condensations (called ϕ) in the scenario where the scalar field ϕonce dominates the universe. In such a scenario, the cosmic microwave background (CMB) radiation originates to decay products of the scalar condensation and hence its anisotropy is affected by the fluctuation of ϕ. It is shown that the present cosmic density perturbations can be dominantly induced from the primordial fluctuation of ϕ, not from the fluctuation of the inflaton field. This scenario may change constraints on the source of the density perturbations, like inflation. In addition, a correlated mixture of adiabatic and isocurvature perturbations may arise in such a scenario; possible signals in the CMB power spectrum are discussed. We also show that the simplest scenario of generating the cosmic density perturbations only from the primordial fluctuation of ϕ(i.e., so-called ``curvaton'' scenario) is severely constrained by the current measurements of the CMB angular power spectrum if correlated mixture of the adiabatic and isocurvature perturbations are generated.

hep-ph↗

arXiv2002

Isocurvature Fluctuations in Tracker Quintessence Models

We consider effects of the isocurvature perturbation in the framework of the tracker-type quintessence models. During the inflation, fluctuations in the amplitude of the quintessence field are generated, which provide isocurvature component of the cosmic density perturbation. Contrary to the conventional notion, it is shown that effects of the isocurvature fluctuation may become sizable in some cases, and in particular, the cosmic microwave background angular power spectrum may be significantly enhanced due to the effect of the isocurvature mode. Such an enhancement may be detectable in on-going and future experiments.

astro-ph↗

arXiv2002

Anomaly-Mediated Supersymmetry Breaking with Axion

We construct hadronic axion models in the framework of the anomaly-mediated supersymmetry breaking scenario. If the Peccei-Quinn symmetry breaking is related to the supersymmetry breaking, mass spectrum of the minimal anomaly-mediated scenario is modified, which may solve the negative slepton mass problem in the minimal anomaly-mediated model. We find several classes of phenomenologically viable models of axion within the framework of the anomaly mediation and, in particular, we point out a new mechanism of stabilizing the axion potential. In this class of models, the Peccei-Quinn scale is related to the messenger scale. We also study phenomenological aspects of this class of models. We will see that, in some case, the lightest particle among the superpartners of the standard-model particles is stau while the lightest superparticle becomes the axino, the superpartner of the axion. With such a unique mass spectrum, conventional studies of the collider physics and cosmology for supersymmetric models should be altered.

hep-ph↗

arXiv2001

Cosmic Microwave Background Anisotropy with Late Time Entropy Production

We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field ϕonce dominates the universe, the CMB we observe today is from the decay of ϕand its anisotropy is affected by the primordial fluctuation in the amplitude of the modulus field. As a result, constraints on the inflaton potential from the CMB anisotropy can be relaxed. In addition, with the cosmological moduli fields, correlated mixture of adiabatic and isocurvature fluctuations may be generated, which results in enhanced CMB angular power spectrum at higher multipoles relative to that of lower ones. Such an enhancement can be an evidence of late time entropy production due to the cosmological moduli fields, and may be observed at on-going and future experiments.

hep-ph↗

arXiv2001

Muon Magnetic Dipole Moment and Higgs Mass in Supersymmetric SU(5) Models

We study the muon magnetic dipole moment and the Higgs mass in the framework of the supersymmetric SU(5) models. In this analysis, all the relevant parameters in the Lagrangian are taken to be free; in particular, assumption of the universal scalar mass is not adopted. Negative search for the Higgs boson at the LEP II experiment sets an important constraint on the supersymmetric contribution to the muon magnetic dipole moment a_μ(SUSY). It is shown that, for a fixed value of the lightest Higgs mass, the maximum possible value of a_μ(SUSY) becomes significantly larger in the general SU(5) case compared to the case of the universal scalar mass (i.e., the case of the so-called ``CMSSM''). We also point out that, if we take relatively large value of the trilinear scalar couplings, the constraint from the Higgs mass is drastically relaxed. In this case, a_μ(SUSY) can be as large as \sim 50\times 10^{-10} even for small value of \tanβ(say, for \tanβ=5).

hep-ph↗

arXiv2001

Cosmic Microwave Background Anisotropy with Cosine-Type Quintessence

We study the Cosmic Microwave Background (CMB) anisotropies produced by cosine-type quintessence models. In our analysis, effects of the adiabatic and isocurvature fluctuations are both taken into account. For purely adiabatic fluctuations with scale invariant spectrum, we obtain a stringent constraint on the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA. Furthermore, it is shown that isocurvature fluctuations have significant effects on the CMB angular power spectrum at low multipoles in some parameter space, which may be detectable in future satellite experiments. Such a signal may be used to test the cosine-type quintessence models.

astro-ph↗

arXiv2001

CP Violation in Kaon System in Supersymmetric SU(5) Model with Seesaw-Induced Neutrino Masses

CP violations in the kaon system are studied in supersymmetric SU(5) model with right-handed neutrinos. We pay a special attention to the renormalization group effect on the off-diagonal elements of the squark mass matrices. In particular, if the Yukawa couplings and mixings in the neutrino sector are sizable, off-diagonal elements of the right-handed down-type squark mass matrix are generated, which affect CP and flavor violations in decay processes of the kaon. We calculate supersymmetric contributions to epsilon (as well as Delta m_K), Br(K_L -> pi^0 nu \bar{nu}), and epsilon'/epsilon in this framework. We will see that the supersymmetric contribution to the epsilon parameter can be as large as (and in some case, larger than) the experimentally measured value. We also discuss its implication to future tests of the unitarity triangle of the Kobayashi-Maskawa matrix.

hep-ph↗

arXiv2001

No-Scale Scenarios in the Light of New Measurement of Muon Anomalous Magnetic Moment

Supersymmetric contribution to the muon anomalous magnetic moment a_μis discussed in the no-scale-type supersymmetry breaking scenarios. Taking the correlation between the supersymmetric contributions to a_μand Br(b\to sγ), it is shown that the precise measurements of these quantities serve an important constraint on the relative sign of the gaugino masses; combining the 2.6-σdeviation in a_μfrom the standard-model prediction measured by the E821 experiment and Br(b\to sγ) measured by CLEO, the sign of the product M_2M_3 is strongly preferred to be positive, where M_2 and M_3 are SU(2)_L and SU(3)_C gaugino mass parameters, respectively. In particular, no-scale-type models with universal gaugino masses are in accord with the two constraints and also with the Higgs mass bound. In addition, it is also shown that future improvements in the measurements of a_μand Br(b\to sγ) may provide serious test of the cases with M_2M_3<0.

hep-ph↗

arXiv2001

Recent Result from E821 Experiment on Muon g-2 and Unconstrained Minimal Supersymemtric Standard Model

Recently, the E821 experiment at the Brookhaven National Laboratory announced their latest result of their muon g-2 measurement which is about 2.6-σaway from the standard model prediction. Taking this result seriously, we examine the possibility to explain this discrepancy by the supersymmetric contribution. Our analysis is performed in the framework of the unconstrained supersymmetric standard model which has free seven parameters relevant to muon g-2. We found that, in the case of large \tanβ, sparticle masses are allowed to be large in the region where the SUSY contribution to the muon g-2 is large enough, and hence the conventional SUSY search may fail even at the LHC. On the contrary, to explain the discrepancy in the case of small \tanβ, we found that (i) sleptons and SU(2)_L gauginos should be light, and (ii) negative search for the Higgs boson severely constrains the model in the framework of the mSUGRA and gauge-mediated model.

hep-ph↗

arXiv2001

Constraints on Natural Inflation from Cosmic Microwave Background

We study constraints on the natural inflation model from the cosmic microwave background radiation (CMBR). Inflaton ϕfor the natural inflation has a potential of the form V=Λ^4[1-\cos(ϕ/\sqrt{2}f_ϕ)], which is parametrized by two parameters f_ϕand Λ. Various cosmological quantities, like the primordial curvature perturbation and the CMBR anisotropy, are determined as functions of these two parameters. Using recent observations of the CMBR anisotropy by BOOMERANG and MAXIMA (as well as those from COBE), constraints on the parameters f_ϕand Λare derived. The model with f_ϕlower than 8.5\times 10^{18} (5.4\times 10^{18}, 4.5\times 10^{18}) GeV predicts a power spectrum with index n_{\rm S} smaller than 0.95 (0.9, 0.85) which suppresses the CMBR anisotropy for smaller angular scale. With such a small n_{\rm S}, height of the second acoustic peak can become significantly lower than the case of the scale-invariant Harrison-Zeldovich spectrum.

hep-ph↗

arXiv2000

Radiative decay of a massive particle and the non-thermal process in primordial nucleosynthesis

We consider the effects on big bang nucleosynthesis (BBN) of the radiative decay of a long-lived massive particle. If high-energy photons are emitted after the BBN epoch ($t \sim 1 - 10^3$ sec), they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between standard BBN and observation. Taking into account recent observational and theoretical developments in this field, we revise our previous study constraining the abundance of the radiatively-decaying particles. In particular, on the theoretical side, it was recently claimed that the non-thermal production of $^6$Li, which is caused by the photodissociation of $\hefour$, most severely constrains the abundance of the radiatively-decaying particle. We will see, however, it is premature to emphasize the importance of the non-thermal production of $^6$Li because (i) the theoretical computation of the $^6$Li abundance has large uncertainty due to the lack of the precise understanding of the $^6$Li production cross section, and (ii) the observational data of $^6$Li abundance has large errors.

hep-ph↗

arXiv2000

Quantum Inconsistency of Einstein Supergravity

We show that N=1, D=4 Einstein-frame supergravity is inconsistent at one loop because of an anomaly in local supersymmetry transformations. A Jacobian must be added to the Einstein-frame Lagrangian to cancel this anomaly. We show how the Jacobian arises from the super-Weyl field redefinition that takes the superspace Lagrangian to the Einstein frame. We present an explicit example which demonstrates that the Jacobian is necessary for one-loop scattering amplitudes to be frame independent.

hep-th↗

arXiv2000

CP violation in B_d \to ϕK_S in SUSY GUT with right-handed neutrinos

CP violation in the B_d system is discussed in the supersymmetric grand unified theory (GUT) with the right-handed neutrinos. Above the GUT scale, the right-handed down-type squarks couple to the right-handed neutrinos. Due to the renormalization group effect, flavor violations in the lepton sector may be transfered to the right-handed down-type squark mass matrix, which affects the CP violation in the B decay. Taking into account this effect, we compare the CP violation in B_d \to ψK_S and B_d \to ϕK_S processes. We will find that a significant difference is possible between the CP violating phases in two decay processes.

hep-ph↗

arXiv2000

Anomaly mediation in supergravity theories

We consider the effects of anomalies on the supersymmetry-breaking parameters in supergravity theories. We construct a supersymmetric expression for the anomaly-induced terms in the 1PI effective action; we use this result to compute the complete one-loop formula for the anomaly-induced gaugino mass. The mass receives contributions from the super-Weyl, Kahler, and sigma-model anomalies of the supergravity theory. We point out that the anomaly-mediated gaugino mass can be affected by local counterterms that cancel the super-Weyl-Kahler anomaly. This implies that the gaugino mass cannot be predicted unless the full high-energy theory is known.

hep-th↗

arXiv2000

Naturalness Re-examined: Implications for Supersymmetry Searches

We discuss the origin of "focus points" in the scalar mass RGEs of the MSSM and their implications for collider searches. We present a new exact analytic solution to the homogeneous system of scalar mass RGEs in the MSSM for general $\tanβ$. This is then used to prove that the focus point for $m^2_{H_u}$ depends only on the value of the top Yukawa coupling at the {\em weak} scale (not its value at the GUT scale) and is independent of the bottom Yukawa coupling.

hep-ph↗

arXiv2000

Effects of the right-handed neutrinos on ΔS = 2 and ΔB = 2 processes in supersymmetric SU(5) model

We discuss an extra source of CP and flavor violations in supersymmetric SU(5) grand unified model with the right-handed neutrinos. In such a model, the right-handed down-type squarks \tilde{d}_R interact with the right-handed neutrinos above the GUT scale, and the renormalization group effect can generate sizable off-diagonal elements in the mass matrix of \tilde{d}_R. Because of new Yukawa phases which exist in the SU(5) model, these off-diagonal elements have, in general, large CP violating phases. The renormalization group induced off-diagonal elements affect the K and B decays. In particular, in this model, supersymmetric contribution to the ε_K parameter can be as large as the currently measured experimental value, and hence the effect might be seen as an anomaly in the on-going test of the Cabibbo-Kobayashi-Maskawa triangle.

hep-ph↗

arXiv1999

Focus Points and Naturalness in Supersymmetry

We analyze focus points in supersymmetric theories, where a parameter's renormalization group trajectories meet for a family of ultraviolet boundary conditions. We show that in a class of models including minimal supergravity, the up-type Higgs mass has a focus point at the weak scale, where its value is highly insensitive to the universal scalar mass. As a result, scalar masses as large as 2 to 3 TeV are consistent with naturalness, and {\em all} squarks, sleptons and heavy Higgs scalars may be beyond the discovery reaches of the Large Hadron Collider and proposed linear colliders. Gaugino and Higgsino masses are, however, still constrained to be near the weak scale. The focus point behavior is remarkably robust, holding for both moderate and large \tanβ, any weak scale gaugino masses and A parameters, variations in the top quark mass within experimental bounds, and for large variations in the boundary condition scale.

hep-ph↗

arXiv1999

The Minimal Supersymmetric Leptogenesis

We reanalyze the supersymmetric leptogenesis model by one of the authors (HM) and Yanagida based on \tilde{L} = H_u flat direction in detail. We point out that the appropriate amount of baryon asymmetry can be generated in this model with the neutrino mass matrix consistent with the atmospheric neutrino oscillation and solutions to the solar neutrino problem, preferably the small angle MSW solution. The reheating temperature can be low enough to avoid the cosmological gravitino problem. This model is the minimal one because it does not rely on any new physics beyond supersymmetry and Majorana neutrino masses.

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