arXiv subjects

Yukihiro Mimura

Publications and source records attributed to Yukihiro Mimura.

At least 37 records · Page 2Linked to original sources

arXiv2014

Hilltop Supernatural Inflation and SUSY Unified Models

In this paper, we consider high scale (100 TeV) supersymmetry (SUSY) breaking and realize the idea of hilltop supernatural inflation in concrete particle physics models based on flipped-SU(5) and Pati-Salam models in the framework of supersymmetric grand unified theories (SUSY GUTs). The inflaton can be a flat direction including right-handed sneutrino and the waterfall field is a GUT Higgs. The spectral index is $n_s=0.96$ which fits very well with recent data by PLANCK satellite. There is no both thermal and non-thermal gravitino problems. Non-thermal leptogenesis can be resulted from the decay of right-handed sneutrino which plays (part of) the role of inflaton.

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arXiv2013

Higgs Pair Production at the LHC and ILC from general potential

Higgs cubic coupling plays a crucial role to probe an origin of electroweak symmetry breaking. It is expected that the cubic coupling is measured by Higgs pair production at the LHC and ILC, and the deviations from the standard model can be extracted from the Higgs pair production process, and those can give us a hint of new physics beyond the standard model. We consider a general potential that achieves the suitable electroweak symmetry breaking. As one of the interesting models, we suggest a non-perturbative Higgs model in which a run-away type of potential is used. In the model, the cross sections of pair production at the LHC is enlarged compared to the standard model. We also study the Higgs pair production induced by a non-canonical kinetic term of Higgs fields which will be important to search the pair-production at the ILC.

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arXiv2013

Proton decay and $μ\to e+γ$ Connection in a Renormalizable SO(10) GUT for Neutrinos

Supersymmetric SO(10) grand unified models with renormalizable Yukawa couplings involving {\bf 10}, {\bf 126} and {\bf 120} Higgs fields have been shown to give a very economical theory for understanding quark-lepton flavor in a unified framework. In previous papers, we showed how nucleon decay can be suppressed in these models without invoking cancellation, by choice of Yukawa flavor texture within a type II seesaw framework for neutrinos that explains all mixings and masses including the recently observed "large" $θ_{13}$. In this follow-up paper, we extend our earlier work to the case of type I seesaw and show that the recently measured "large" $θ_{13}$ can be accommodated in this case while suppressing proton decay. We then point out that the two cases (type I and II) lead to different testable predictions for $B(μ\to e+γ)$ and $B(τ\to μ(e) +γ)$ as well as different flavor final states in nucleon decay. In particular, we find that for the type I seesaw case, $B(τ\to μ+γ)$ can be observable while at the same time suppressing $B(μ\to e+γ)$, whereas in the type II seesaw case, $B(τ\to μ+γ)$ is always suppressed whereas $B(μ\to e+γ)$ is observable.

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arXiv2013

Bootstrap Dynamical Symmetry Breaking with New Heavy Chiral Quarks

A Higgs-like new boson with mass around 126 GeV is now established, but its true nature probably cannot be settled with 2011--2012 LHC data. We assume it is a dilaton with couplings weaker than the Higgs boson (except to $γγ$ and $gg$), and explore dynamical symmetry breaking (DSB) by strong Yukawa coupling of a yet unseen heavy chiral quark doublet $Q$. Assuming the actual Higgs boson to be heavy, the Goldstone boson $G$ of electroweak symmetry breaking still couples to $Q$ with Yukawa coupling $λ_Q$. A ``bootstrap" gap equation without a Higgs particle is constructed. Electroweak symmetry breaking via strong $λ_Q$ generates both heavy mass for $Q$, while self-consistently justifying $G$ as a massless Goldstone particle in the loop. The spontaneous breaking of scale invariance in principle \emph{allows} for a dilaton. We numerically solve such a gap equation and find the mass of the heavy quark to be a couple of TeV. We offer a short critique on the results of the scale-invariant model of Hung and Xiong, where a similar gap equation is built with a massless scalar doublet. Through this we show that a light SM Higgs at 126 GeV cannot be viable within our approach to DSB, while a dilaton with weaker couplings is consistent with our main result.

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arXiv2013

Enhancement of Higgs to diphoton decay width in non-perturbative Higgs model

We investigate a possibility if a loop diagram via Higgsino can enhance the Higgs to diphoton decay width in supersymmetric models with an extension of Higgs sector. A model with an additional non-renormalizable term of Higgs fields is firstly analyzed where the higher order term can introduce the Higgs coupling to Higgsinos as well as charged Higgs bosons. We point out that a choice of the Higgs coupling to obtain a significant size of enhancement of diphoton decay width reduces the Higgs mass and/or a size of non-renormalizable term needs to be large and a cutoff scale is around the weak scale. Another model in which the Higgsino mass term is generated by a non-perturbative instanton effect via a strong dynamics in a context of SUSY QCD is also suggested. It is shown that the sign of the Higgs coupling to fermions is opposite from perturbative models due to an operator including bosonic fields in the denominator and a constructive contribution to the diphoton decay amplitude can be easily obtained in this kind of model.

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arXiv2012

Colored Scalars And The CDF $W+$dijet Excess

The recent data on $W+$dijet excess reported by CDF may be interpreted as the associated production of a $W$ and a new particle of mass about 150 GeV which subsequently decays into two hadron jets. We study the possibility of explaining the $W+$dijet excess by colored scalar bosons. There are several colored scalars which can have tree level renormalizable Yukawa couplings with two quarks, $({\bf 8}, {\bf 2},1/2)$, $(\bar{\bf 6}({\bf 3}), {\bf 3}({\bf 1}), -1/3)$, $(\bar {\bf 6}({\bf 3}), {\bf 1}, -4/3(2/3))$. If one of these scalars has a mass about 150 GeV, being colored it can naturally explain why the excess only shows up in the form of two hadron jets. Although the required production cross section and mass put constraints on model parameters and rule out some possible scenarios when confronted with other existing data, in particular FCNC data, we find that there are strong constraints on the Yukawa couplings of these scalars. Without forcing the couplings to be some special texture forms most of the scalars, except the $({\bf 3}, {\bf 3}, -1/3)$, are in trouble with FCNC data. We also study some features for search of these new particles at the RHIC and the LHC and find that related information can help further to distinguish different models.

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arXiv2011

TeV-scale seesaw with non-negligible left-right neutrino mixings

We suggest natural TeV-scale seesaw with non-negligible left-right neutrino mixings as preserving tiny neutrino masses. Our analysis is exhibited, without loss of generality, by taking a basis of the neutrino matrices, in which the condition to obtain the left-right mixings is clear. We also suggest a flavor symmetry as an underlying theory, which naturally realizes our setup to preserve tiny neutrino masses. Our setup can predict a magnitude of sin theta_13 in a region of 0.10 to 0.20, depending on the deviation from maximal atmospheric neutrino mixing and CP phase. We also investigate experimental constraints and phenomenology in our setup.

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arXiv2011

B_s --> mu+mu- in Supersymmetric Grand Unified Theories

We investigate the recent CDF measurement of the Br(B_s --> mu+mu-) which shows excess over the Standard Model. We consider minimal supergravity motivated models (mSUGRA)/CMSSM and grand unified models, SU(5) and SO(10). In the grand unified models, the neutrino mixings provide an additional source of squark flavor violation through the quark-lepton unification. In the context of minimal SU(5) model, we find that the new CDF measurement has imposed a lower bound on the branching ratio of tau --> mu gamma for a large CP phase in the B_s-bar B_s mixing. Recall that there have been indication for a large CP phase in B_s mixing from B_s --> J/psi phi (Tevatron and LHCb) and dimuon asymmetry (D0). We also predict Br(tau --> mu eta) for the possible range of values of Br(tau --> mu gamma).

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arXiv2011

Dimuon CP Asymmetry in B Decays and Wjj Excess in Two Higgs Doublet Models

We analyze the puzzle of the dimuon CP asymmetry in B_s decays in two Higgs doublet models. We show that the flavor changing neutral current (FCNC) induced by the Higgs coupling in a type III two Higgs doublet model provides a solution to the dimuon charge asymmetry puzzle by enhancing the absorbtive part of the mixing amplitude Γ_{12}^s. We investigate different experimental constraints and show that it is possible to enhance Γ_{12}^s in order to explain the dimuon asymmetry observed by D0. This enhancement requires large Higgs couplings to the first and second generations of quarks which may also explain the recent 3.2 σWjj excess observed by CDF.

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arXiv2010

Direct and Indirect Detection and LHC Signals of Bino-Higgsino Dark Matter

If the lightest dark matter neutralino has a sufficiently large Higgsino component, its spin-independent and spin-dependent cross sections on nucleons can be sizable enough to be detected soon in direct and indirect surveys. We outline in this paper some characteristic features expected of mixed bino-Higgsino dark matter. If the observed relic density is saturated by the bino-Higgsino dark matter, it fixes the amount of allowable bino-Higgsino mixing and provides predictions for other observables which can be tested at the Large Hadron Collider (LHC). We study the correlation between the cross sections and the branching ratio of B_s -> mu^+ mu^-. For a mixed bino-Higgsino dark matter, the mass differences of the neutralinos can be less than M_Z. This will cause an excess of lepton pairs, above the Standard Model predictions, from the decays of the two heavier neutralinos. We discuss implications of the dilepton invariant mass distribution, and outline a way to extract the neutralino parameters for testing gaugino mass unification and deducing the relic density from an interplay of astrophysical detection and LHC measurements.

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arXiv2010

CP Violating Lepton Asymmetry from B Decays in Supersymmetric Grand Unified Theories

We investigate the effect of the dimuon CP asymmetry from the B decay modes, recently observed at 3.2 sigma deviation from the Standard Model (SM) by the D0 collaboration, in the context of SU(5) and SO(10) GUT models. We exhibit that a large amount of flavor violation between the second and the third generation is generated due to the large neutrino atmospheric mixing angle and this flavor violation can be responsible for the observed large CP asymmetry due to the presence of new phases (not present in the CKM matrix) in the Yukawa couplings. We also study the implication of the parameter space in these GUT models with large CP violating lepton asymmetry for different phenomenologies, e.g., Br(tau -> mu + gamma), Br(B_s -> mu + mu) at the Fermilab, direct detection of dark matter (DM) in the ongoing detectors and measurement of muon flux from solar neutrinos at the IceCube experiment.

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arXiv2010

An SO(10) Grand Unified Theory of Flavor

We present a supersymmetric SO(10) grand unified theory (GUT) of flavor based on an $S_4$ family symmetry. It makes use of our recent proposal to use SO(10) with type II seesaw mechanism for neutrino masses combined with a simple ansatz that the dominant Yukawa matrix (the {\bf 10}-Higgs coupling to matter) has rank one. In this paper, we show how the rank one model can arise within some plausible assumptions as an effective field theory from vectorlike {\bf 16} dimensional matter fields with masses above the GUT scale. In order to obtain the desired fermion flavor texture we use $S_4$ flavon multiplets which acquire vevs in the ground state of the theory. By supplementing the $S_4$ theory with an additional discrete symmetry, we find that the flavon vacuum field alignments take a discrete set of values provided some of the higher dimensional couplings are small. Choosing a particular set of these vacuum alignments appears to lead to an unified understanding of observed quark-lepton flavor: (i) the lepton mixing matrix that is dominantly tri-bi-maximal with small corrections related to quark mixings; (ii) quark lepton mass relations at GUT scale: $m_b\simeq m_τ$ and $m_μ\simeq 3 m_s$ and (iii) the solar to atmospheric neutrino mass ratio $m_\odot/m_{\rm atm}\simeq θ_{\rm Cabibbo}$ in agreement with observations. The model predicts the neutrino mixing parameter, $U_{e3} \simeq θ_{\rm Cabibbo}/(3\sqrt2) \sim 0.05$, which should be observable in planned long baseline experiments.

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arXiv2010

Color Triplet Diquarks at the LHC

We consider a class of supersymmetric models containing baryon number violating processes such as observable neutron - antineutron oscillations that are mediated by color triplet diquark fields. For plausible values of the diquark-quark couplings, the scalar diquark with mass between a few hundred GeV and one TeV or so can be produced in the s-channel at the LHC and detected through its decay into a top quark and a hadronic jet.

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arXiv2009

Observable n - anti-n Oscillations with New Physics at LHC

We explore extensions of the MSSM in which TeV scale vector-like multiplets can mediate observable n-anti-n oscillations, without causing conflict with the proton decay experiments, with a U(1) symmetry playing an important role. The colored vector-like particles, in particular, may be found at the LHC through some decay modes arising from their direct couplings to quarks.

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arXiv2009

Origin of Quark-Lepton Flavor in SO(10) with Type II Seesaw

Diverse mass and mixing patterns between the quarks and leptons makes it challenging to construct a simple grand unified theory of flavor. We show that SO(10) SUSY GUTs with type II seesaw mechanism giving neutrino masses provide a natural framework for addressing this issue. A simple ansatz that the dominant Yukawa matrix (the 10-Higgs coupling to matter) has rank one, appears to simultaneously explain both the large lepton mixings as well as the observed quark flavor hierarchy in these models. A testable prediction of this ansatz is the neutrino mixing, U_{e3}, which should be observable in planned long baseline experiments.

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arXiv2009

Correlation between direct dark matter detection and Br(B_s -> mu mu) with a large phase of B_s - anti-B_s mixing

We combine the analyses for flavor changing neutral current processes and dark matter solutions in minimal-type supersymmetric grand unified theory (GUT) models, SO(10) and SU(5), with a large B_s - anti-B_s mixing phase and large tan beta. For large tan beta, the double penguin diagram dominates the SUSY contribution to the B_s - anti-B_s mixing amplitude. Also, the Br(B_s -> mu mu) constraint becomes important as it grows as tan^6 beta, although it can still be suppressed by large pseudoscalar Higgs mass m_A. We investigate the correlation between B_s -> mu mu and the dark matter direct detection cross-section through their dependence on m_A. In the minimal-type of SU(5) with type I seesaw, the large mixing in neutrino Dirac couplings results in large lepton flavor violating decay process tau to mu gamma, which in turn sets upper bound on m_A. In the SO(10) case, the large mixing can be chosen to be in the Majorana couplings instead, and the constraint from Br(tau -> mu gamma) can be avoided. The heavy Higgs funnel region turns out to be an interesting possibility in both cases and the direct dark matter detection should be possible in the near future in these scenarios.

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arXiv2009

Flavor Symmetry in Gauge-Higgs-Matter Unified Orbifold GUTs

We construct an orbifold model in which all the standard model particles are unified in a gauge multiplet in higher dimensional supersymmetric gauge theory. We find that a flavor symmetry has to remain in four dimensions due to the discrete charge conservation for orbifold conditions if the colored Higgs components in the gauge multiplet are projected out. When the flavor symmetry originates from the E_8 bulk gauge symmetry, the successful unification model can be constructed. In the model, all the Dirac Yukawa couplings for quarks and leptons are generated by the higher dimensional gauge interaction.

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arXiv2009

Three family unification in higher dimensional models

In orbifold models, gauge, Higgs and the matter fields can be unified in one multiplet from the compactification of higher dimensional supersymmetric gauge theory. We study how three families of chiral fermions can be unified in the gauge multiplet. The bulk gauge interaction includes the Yukawa interactions to generate masses for quarks and leptons after the electroweak symmetry is broken. The bulk Yukawa interaction has global or gauged flavor symmetry originating from the R symmetry or bulk gauge symmetry, and the Yukawa structure is restricted. When the global and gauged flavor symmetries are broken by orbifold compactification, the remaining gauge symmetry which contains the standard model gauge symmetry is restricted. The restrictions from the bulk flavor symmetries can provide explanations of fermion mass hierarchy.

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