arXiv subjects

T. Yanagida

Publications and source records attributed to T. Yanagida.

At least 19 recordsLinked to original sources

arXiv2006

Hard X-ray Detector (HXD) on Board Suzaku

The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit back ground based on a combination of new techniques, including the concept of well-type active shield counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV, the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (~5 degree). The on-board signal-processing system and the data transmitted to the ground are also described.

astro-ph↗

arXiv2006

In-Orbit Performance of the Hard X-ray Detector on board Suzaku

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600 keV, energy resolutions of ~4 keV (FWHM) at 40 keV and ~11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

astro-ph↗

arXiv2006

Product-Group Unification in Type IIB String Thoery

The product-group unification is a model of unified theories, in which masslessness of the two Higgs doublets and absence of dimension-five proton decay are guaranteed by a symmetry. It is based on SU(5) x U(N) (N=2,3) gauge group. It is known that various features of the model are explained naturally, when it is embedded in a brane world. This article describes an idea of how to accommodate all the particles of the model in Type IIB brane world. The GUT-breaking sector is realized by a D3--D7 system, and chiral quarks and leptons arise from intersection of D7-branes. The D-brane configuration can be a geometric realization of the non-parallel family structure of quarks and leptons, an idea proposed to explain the large mixing angles observed in the neutrino oscillation. The tri-linear interaction of the next-to-minimal supersymmetric standard model is obtained naturally in some cases.

hep-ph↗

arXiv2006

Leptogenesis as the origin of matter

We explore in some detail the hypothesis that the generation of a primordial lepton-antilepton asymmetry (Leptogenesis) early on in the history of the Universe is the root cause for the origin of matter. After explaining the theoretical conditions for producing a matter-antimatter asymmetry in the Universe we detail how, through sphaleron processes, it is possible to transmute a lepton asymmetry -- or, more precisely, a (B-L)-asymmetry -- into a baryon asymmetry. Because Leptogenesis depends in detail on properties of the neutrino spectrum, we review briefly existing experimental information on neutrinos as well as the seesaw mechanism, which offers a theoretical understanding of why neutrinos are so light. The bulk of the review is devoted to a discussion of thermal Leptogenesis and we show that for the neutrino spectrum suggested by oscillation experiments one obtains the observed value for the baryon to photon density ratio in the Universe, independently of any initial boundary conditions. In the latter part of the review we consider how well Leptogenesis fits with particle physics models of dark matter. Although axionic dark matter and Leptogenesis can be very naturally linked, there is a potential clash between Leptogenesis and models of supersymmetric dark matter because the high temperature needed for Leptogenesis leads to an overproduction of gravitinos, which alter the standard predictions of Big Bang Nucleosynthesis. This problem can be resolved, but it constrains the supersymmetric spectrum at low energies and the nature of the lightest supersymmetric particle (LSP). Finally, as an illustration of possible other options for the origin of matter, we discuss the possibility that Leptogenesis may occur as a result of non-thermal processes.

hep-ph↗

arXiv2006

Conformally Sequestered SUSY Breaking in Vector-like Gauge Theories

We provide, in a framework of vector-like gauge theories, concrete models for conformal sequestering of dynamical supersymmetry (SUSY) breaking in the hidden sector. If the sequestering is sufficiently strong, anomaly mediation of the SUSY breaking may give dominant contributions to the mass spectrum of SUSY standard-model particles, leading to negative slepton masses squared. Thus, we also consider a model with gravitational gauge mediation to circumvent the tachyonic slepton problem in pure anomaly mediation models.

hep-ph↗

arXiv2005

A Higher-dimensional Origin of the Inverted Mass Hierarchy for Neutrino

We present successful lepton mass matrices with an inverted mass hierarchy for neutrinos, which follow from a geometrical structure of a (1+5) dimensional space-time where two extra dimensions are compactified on the T^2/Z_3 orbifold. A 5^* and a right-handed neutrino N in each family are localized on each of the equivalent three fixed points of the orbifold while three 10's and Higgs doublets H_u and H_d live in the bulk. An S_3 family symmetry is assumed on three 5^*'s and on three N's, since the three fixed points are equivalent to one another. The Higgs field ϕresponsible for the B-L breaking is localized on one of the three fixed points, which generates the inverted hierarchy for the neutrino masses. The baryon asymmetry is well explained in the non-thermal leptogenesis via inflaton decay. We emphasize that the present model predicts the effective neutrino mass, _{ee}, responsible for neutrinoless double beta decays as _{ee}\simeq 50 meV. This will be accessible to future experiments.

hep-ph↗

arXiv2005

More on Conformally Sequestered SUSY Breaking

We extend our models for conformal sequestering of dynamical supersymmetry breaking with decoupling vector-like matter in several different ways. These extensions enable us to simplify concrete model building, in particular, rendering large gauge group and ad hoc global symmetry for sequestering unnecessary. Conformal sequestering appears highly natural in such circumstances.

hep-ph↗

arXiv2005

511 keV Gamma Ray from Moduli Decay in the Galactic Bulge

We show that the $e^++e^-$ decay of a light scalar boson of mass 1-10 MeV may account for the fluxes of 511 keV gamma ray observed by SPI/INTEGRAL. We argue that candidates of such a light scalar boson is one of the string moduli or a scalar partner of the axion in a supersymmetric theory.

hep-ph↗

arXiv2005

On Myosin II dynamics in the presence of external loads

We address the controversial hot question concerning the validity of the loose coupling versus the lever-arm theories in the actomyosin dynamics by re-interpreting and extending the phenomenological washboard potential model proposed by some of us in a previous paper. In this new model a Brownian motion harnessing thermal energy is assumed to co-exist with the deterministic swing of the lever-arm, to yield an excellent fit of the set of data obtained by some of us on the sliding of Myosin II heads on immobilized actin filaments under various load conditions. Our theoretical arguments are complemented by accurate numerical simulations, and the robustness of the model is tested via different choices of parameters and potential profiles.

q-bio.SC↗

arXiv2005

Dark Matter and Baryon Asymmetry of the Universe in Large-Cutoff Supergravity

We propose a consistent scenario of the evolution of the universe based on the large cutoff supergravity (LCSUGRA) hypothesis of supersymmetry breaking, where the gravitino and sfermion become as heavy a $\sim O(1-10 {\rm TeV})$. With such a heavy gravitino, baryon asymmetry of the universe can be generated by the non-thermal leptogenesis via an inflaton decay without conflicting the serious gravitino problem. We also see that, in the LCSUGRA scenario, relic density of the lightest superparticle becomes consistent with the WMAP value of the dark matter density in the parameter region required for the successful non-thermal leptogenesis.

hep-ph↗

arXiv2005

Strongly Coupled Gauge Mediation

A model of gauge mediation with the gravitino mass of order 1eV is considered to motivate 100TeV colliders. Massive mediators with standard-model and supersymmetry-breaking gauge quantum numbers let low-scale dynamics induce sizable soft masses of the standard-model superpartners. We circumvent potential phenomenological difficulties that such low-scale models tend to cause.

hep-ph↗

arXiv2004

Testing the see-saw mechanism at collider energies

We propose a low energy extension of the Standard Model consisting of an additional gauged $U(1)_{B-L}$ plus three right-handed neutrinos. The lightest right-handed neutrinos have TeV scale masses and may be produced at colliders via their couplings to the $Z_{B-L}$ gauge boson whose mass and gauge coupling is constrained by the out-of-equilibrium condition leading to upper bounds on the right-handed neutrino and $Z_{B-L}$ production cross-sections at colliders. We propose a brane-world scenario which motivates such TeV mass right-handed neutrinos. Our analysis opens up the possibility that the mechanism responsible for neutrino mass is testable at colliders such as the LHC or VLHC.

hep-ph↗

arXiv2004

A Phenomenological model of Myosin II dynamics in the presence of external loads

q-bio.BM↗

arXiv2004

Realization of Minimal Supergravity

Minimal supergravity mediation of supersymmetry breaking has attracted much attention due to its simplicity, which leads to its predictive power. We consider how Nature possibly realizes minimal supergravity through inflationary selection of the theory. Minimality is impressively consistent with the present observational bounds and it might be tested with the aid of low-energy soft parameters obtained in future experiments.

hep-ph↗

arXiv2004

A solution to the baryon and dark-matter coincidence puzzle in a $\tilde{N}$ dominated early universe

If a bosonic partner of a right-handed neutrino dominates the early universe sufficiently before its decay, important ingredients in the present universe are related to physics of the right-handed neutrino sector. In particular, we find that the ratio of the baryon to the dark-matter densities is given only by low-energy parameters such as a neutrino mass and a gravitino mass if the reheating temperature of inflation is much higher than $10^{12}$ GeV. Here, the gravitino is assumed to be the lightest supersymmetric particle and the dominant component of the dark matter. The observed ratio, $Ω_{B}/Ω_{DM} \simeq 0.21\pm 0.04$, suggests the mass of the gravitino to be in the range of $\cal O$(10) MeV provided the CP violating phase is of the order 1.

hep-ph↗

arXiv2004

GUT Phase Transition and Hybrid Inflation

The supersymmetric model of hybrid inflation is interesting not only because of its naturalness but also because of another reason. Its energy scale determined by the COBE normalization is 10^15 - 10^16 GeV. It happens to be the energy scale of interest in particle physics, namely, the mass scale of right-handed neutrinos or the energy scale of the gauge-coupling unification. It is true that topological defects are produced after the hybrid inflation if it is related to a U(1)_B-L or a GUT-symmetry breaking, and hence one cannot naively identify models of particle physics with that of inflation. But those defects are not necessarily found in modified models. We show in this article that quite a simple extension of the minimal supersymmetric hybrid inflation model is free from monopoles or cosmic strings. Moreover, it happens to be exactly the same as a well-motivated extension of SU(5)-unified theories. The vacuum energy is dominated by F-term. The η-problem is not necessarily serious when the model is realized by D-branes. Although it has been considered that a coupling constant has to be very small when the vacuum energy is dominated by F-term, this constraint is not applied either to the D-brane model. They are due to a particular form of the Kahler potential and interaction of the model. Reheating process is also discussed.

hep-ph↗

arXiv2004

Super- and CP-symmetric QCD in Higher Dimensions

An extremely precise global symmetry is necessary in the Peccei--Quinn solution to the strong CP problem. Such symmetry arises when colored chiral fermions are localized in an internal space. We present a supersymmetric model that incorporates the above mechanism. Extra colored chiral multiplets around the supersymmetry-breaking scale are a generic prediction of the supersymetric model.

hep-ph↗

arXiv2003

Upper Bound On Gluino Mass From Thermal Leptogenesis

Thermal leptogenesis requires the reheating temperature $T_R \gsim 3\times 10^{9}$ GeV, which contradicts a recently obtained constraint on the reheating temperature, $T_R \lsim 10^6$ GeV, for the gravitino mass of 100 GeV-10 TeV. This stringent constraint comes from the fact that the hadronic decays of gravitinos destroy very efficiently light elements produced by the Big-Bang nucleosynthesis. However, it is not applicable if the gravitino is the lightest supersymmetric particle (LSP). We show that this solution to the gravitino problem works for the case where the next LSP is a scalar charged lepton or a scalar neutrino. We point out that there is an upper bound on the gluino mass as $m_{\rm gluino} \lsim 1.8$ TeV so that the energy density of gravitino does not exceed the observed dark matter density $Ω_{\rm DM}h^2\simeq 0.11$.

hep-ph↗