arXiv subjects

Hitoshi Murayama

Publications and source records attributed to Hitoshi Murayama.

At least 253 records · Page 14Linked to original sources

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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arXiv1999

Can ε'/εbe supersymmetric?

The possible supersymmetric contribution to ε'/εhas been generally regarded small in the literature. We point out, however, that this is a result based on specific assumptions, such as universal scalar mass, and in general needs not to be true. Based on a general situation, (1) hierarchical quark Yukawa matrices protected by flavor symmetry, (2) generic dependence of Yukawa matrices on Polonyi/moduli fields as expected in many supergravity/superstring theories, (3) Cabibbo rotation originating from the down-sector, and (4) phases of order unity, we find the typical supersymmetric contribution to ε'/εto be order 3x10^-3 for m_{\tilde{q}} = 500 GeV. It is even possible that the supersymmetric contribution dominates in the reported KTeV value ε'/ε= (28 \pm 4.1)x10^-4. If so, the neutron electric dipole moment is likely to be within the reach of the currently planned experiments.

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arXiv1999

Seasonal Variations of the 7Be Solar Neutrino Flux

Measuring the 7Be solar neutrino flux is crucial towards solving the solar neutrino puzzle. The Borexino experiment, and possibly the KamLAND experiment, will be capable of studying the 7Be neutrinos in the near future. We discuss (1) how the seasonal variation of the Borexino and KamLAND data can be used to measure the 7Be solar neutrino flux in a background independent way and (2) how anomalous seasonal variations might be used to discover vacuum neutrino oscillations, independent of the solar model and the measurement of the background. In particular, we find that, after three years of Borexino or KamLAND running, vacuum neutrino oscillations can be either established or excluded for almost all values of (sin^2 2 theta, Delta m^2) preferred by the Homestake, GALLEX, SAGE, and Super-Kamiokande data. We also discuss how well seasonal variations of the data can be used to measure (sin^2 2 theta, Delta m^2) in the case of vacuum oscillations.

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arXiv1998

Establishing a nu_{mu,tau} Component in the Solar Neutrino Flux

We point out that the recoil electron kinetic energy spectra in the nu-e elastic scattering are different for incident nu_{e} or nu_{mu,tau}, and hence one can in principle establish the existence of the nu_{mu,tau} component in the solar neutrino flux by fitting the shape of the spectrum. This would be a new model-independent test of the solar neutrino oscillation in a single experiment, free from astrophysical and nuclear physics uncertainties. For the ^7Be neutrinos, it is possible to determine the nu_{mu,tau} component at BOREXINO or KamLAND, if the background is sufficiently low. Note that this effect is different from the distortion in the incident neutrino energy spectrum, which has been discussed in the literature.

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arXiv1998

Gaugino Mass without Singlets

In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the observable sector have been believed to be extremely suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector with specific couplings to the observable sector gauge multiplets. We point out that there is a pure supergravity contribution to gaugino masses at the quantum level arising from the superconformal anomaly. Our results are valid to all orders in perturbation theory and are related to the `exact' beta functions for soft terms. There is also an anomaly contribution to the A terms proportional to the beta function of the corresponding Yukawa coupling. The gaugino masses are proportional to the corresponding gauge beta functions, and so do not satisfy the usual GUT relations.

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arXiv1998

Tau Appearance In Atmospheric Neutrino Interactions

If the correct interpretation of the Super-Kamiokande atmospheric neutrino data is ν_μ-> ν_τoscillation, the contained data sample should already have more than 10 tau appearance events. We study the challenging task of detecting the tau, focussing on the decay chain τ^\pm -> ρ^\pm -> π^\pm π^0 in events with quasi-elastic tau production. The background level, which is currently quite uncertain because of a lack of relevant neutral current data, can be measured by the near detector in the K2K experiment. Our estimates of the background suggest that it may be possible to detect tau appearance in Super-Kamiokande with 5-10 years of running.

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arXiv1998

New Confining N=1 Supersymmetric Gauge Theories

We examine N=1 supersymmetric gauge theories which confine in the presence of a tree-level superpotential. We show the confining spectra which satisfy the 't Hooft anomaly matching conditions and give a simple method to find the confining superpotential. Using this method we fix the confining superpotentials in the simplest cases, and show how these superpotentials are generated by multi-instanton effects in the dual theory. These new type of confining theories may be useful for model building, since the size of the matter content is not restricted by an index constraint. Therefore, one expects that a large variety of new confining spectra can be obtained using such models.

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arXiv1998

Seiberg Duality and e+ e- Experiments

Seiberg duality in supersymmetric gauge theories is the claim that two different theories describe the same physics in the infrared limit. However, one cannot easily work out physical quantities in strongly coupled theories and hence it has been difficult to compare the physics of the electric and magnetic theories. In order to gain more insight into the equivalence of two theories, we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the superconformal window. We describe a technique which allows us to compute the cross sections exactly in the infrared limit. They are indeed equal in the low-energy limit and the equality is guaranteed because of the anomaly matching condition. The ultraviolet behavior of the total ``e+ e-'' cross section is different for the two theories. We comment on proposed non-supersymmetric dualities. We also analyze the agreement of the ``γγ'' and ``WW'' scattering amplitudes in both theories, and in particular try to understand if their equivalence can be explained by the anomaly matching condition.

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arXiv1998

Inflation and flat directions in modular invariant superstring effective theories

The potential during inflation must be very flat in, at least, the direction of the inflaton. In renormalizable global supersymmetry, flat directions are ubiquitous, but they are not preserved in a generic supergravity theory. It is known that at least some of them are preserved in no-scale supergravity, and simple generalizations of it. We here study a more realistic generalization, based on string-derived supergravity, using the linear supermultiplet formalism for the dilaton. We consider a general class of hybrid inflation models, where a Fayet-Illiopoulos $D$ term drives some fields to large values. The potential is dominated by the $F$ term, but flatness is preserved in some directions. This allows inflation, with the dilaton stabilized in its domain of attraction, and some moduli stabilized at their vacuum values. Another modulus may be the inflaton.

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arXiv1998

Study of Inclusive Multi-Ring Events from Atmospheric Neutrinos

The current analysis of atmospheric neutrinos by the Super-Kamiokande Collaboration is based only on fully-contained one-ring events and partially contained events. We show that the up-down ratio of fully-contained, inclusive, multi-ring events gives an independent test of the atmospheric neutrino anomaly, without the need for particle identification. Moreover, this class of events is rich in neutral current events and hence gives crucial information for discriminating between oscillations of ν_μinto ν_{e, τ} and ν_s.

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arXiv1998

Axionic Hot Dark Matter in the Hadronic Axion Window

Mixed dark matter scenario can reconcile the COBE data and the observed large scale structure. So far the massive neutrino with a mass of a few eV has been the only discussed candidate for the hot dark matter component. We point out that the hadronic axion in the so-called hadronic axion window, f_a \sim 10^6 GeV, is a perfect candidate as hot dark matter within the mixed dark matter scenario. The current limits on the hadronic axion are summarized. The most promising methods to verify the hadronic axion in this window are the resonant absorption of almost-monochromatic solar axions from M1 transition of the thermally excited $^{57}$Fe in the Sun, and the observation of the ``axion burst'' in water Čerenkov detectors from another supernova.

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arXiv1998

't Hooft Anomaly Matching for Discrete Symmetries

We show how to extend the 't Hooft anomaly matching conditions to discrete symmetries. We check these discrete anomaly matching conditions on several proposed low-energy spectra of certain strongly interacting gauge theories. The excluded examples include the proposed chirally symmetric vacuum of pure N=1 supersymmetric Yang-Mills theories, certain non-supersymmetric confining theories and some self-dual N=1 supersymmetric theories based on exceptional groups.

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arXiv1998

Regulating the Baryon Asymmetry in No-Scale Affleck-Dine Baryogenesis

In supergravity models (such as standard superstring constructions) that possess a Heisenberg symmetry, supersymmetry breaking by the inflationary vacuum energy does not lift flat directions at tree level. One-loop corrections give small squared masses that are negative (about -g^2 H^2/(4π)^2) for all flat directions that do not involve the stop. After inflation, these flat directions generate a large baryon asymmetry; typically $n_B/s \sim$ O(1). We consider mechanisms for suppressing this asymmetry to the observed level. These include dilution from inflaton or moduli decay, GUT nonflatness of the $vev$ direction, and higher dimensional operators in both GUT models and the MSSM. We find that the observed BAU can easily be generated when one or more of these effects is present.

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arXiv1998

Instantons in Partially Broken Gauge Groups

We discuss the effects of instantons in partially broken gauge groups on the low-energy effective gauge theory. Such effects arise when some of the instantons of the original gauge group G are no longer contained in (or can not be gauge rotated into) the unbroken group H. In cases of simple G and H, a good indicator for the existence of such instantons is the ``index of embedding.'' However, in the general case one has to examine π_3(G/H) to decide whether there are any instantons in the broken part of the gauge group. We give several examples of supersymmetric theories where such instantons exist and leave their effects on the low-energy effective theory.

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arXiv1998

Physics at e^- e^-: a Case for Multi-channel Studies

I argue that it would be crucial to have as many channels as possible to understand the physics of electroweak symmetry breaking (EWSB) in next-generation collider experiments. A historic example of the parity violation and the $V-A$ interaction is used to make this point. An e^- e^- option offers us a new channel in this respect. The usefulness of this channel is exemplified for the case of supersymmetry and of the strongly coupled EWSB sector.

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arXiv1998

Less Minimal Supersymmetric Standard Model

Most of the phenomenological studies of supersymmetry have been carried out using the so-called minimal supergravity scenario, where one assumes a universal scalar mass, gaugino mass, and trilinear coupling at M_{GUT}. Even though this is a useful simplifying assumption for phenomenological analyses, it is rather too restrictive to accommodate a large variety of phenomenological possibilities. It predicts, among other things, that the lightest supersymmetric particle (LSP) is an almost pure B-ino, and that the mu-parameter is larger than the masses of the SU(2)_{L} and U(1)_{Y} gauginos. We extend the minimal supergravity framework by introducing one extra parameter: the Fayet--Iliopoulos D-term for the hypercharge U(1), D_Y. Allowing for this extra parameter, we find a much more diverse phenomenology, where the LSP is \tildeν_τ, \tildeτ or a neutralino with a large higgsino content. We discuss the relevance of the different possibilities to collider signatures. The same type of extension can be done to models with the gauge mediation of supersymmetry breaking. We argue that it is not wise to impose cosmological constraints on the parameter space.

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arXiv1998

Third Generation Familons, B Factories, and Neutrino Cosmology

We study the physics of spontaneously broken family symmetries acting on the third generation. Massless familons (or Majorons) $f$ associated with such broken symmetries are motivated especially by cosmological scenarios with decaying tau neutrinos. We first note that, in marked contrast with the case for the first two generations, constraints on third generation familon couplings are poor, and are, in fact, non-existent at present in the hadronic sector. We derive new bounds from $B^0$--$\bar{B}^0$ mixing, $B^0 \to l^+ l'^-$, $b\to sν\barν$, and astrophysics. The resulting constraints on familon decay constants are still much weaker than those for the first and second generation. We then discuss the promising prospects for significant improvements from searches for $τ\to l f$, $B\to (π, K) f$, and $b\to (d,s) f$ with the current CLEO, ARGUS, and LEP data. Finally, we note that future constraints from CLEO III and the $B$ factories will probe decay constants beyond 10^8 GeV, well within regions of parameter space favored by proposed scenarios in neutrino cosmology.

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arXiv1998

Probing Physics at Short Distances with Supersymmetry

We discuss the prospect of studying physics at short distances, such as Planck length or GUT scale, using supersymmetry as a probe. Supersymmetry breaking parameters contain information on all physics below the scale where they are induced. We will gain insights into grand unification (or in some cases string theory) and its symmetry breaking pattern combining measurements of gauge coupling constants, gaugino masses and scalar masses. Once the superparticle masses are known, it removes the main uncertainty in the analysis of proton decay, flavor violation and electric dipole moments. We will be able to discuss the consequence of flavor physics at short distances quantitatively.

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