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Masaki Asano

Publications and source records attributed to Masaki Asano.

At least 19 recordsLinked to original sources
arXiv2017

Sgoldstino search at the LHC

Low-scale supersymmetry breaking scenario in which the breaking scale is around TeV has been discussed as a possibility to obtain a large Higgs mass and to moderate the fine tuning problem. A characteristic feature is that the hidden sector would be accessible at colliders in such a scenario. In this paper, we investigate the phenomenology of sgoldstino which is the scalar component of the goldstino superfield. We present partial widths and branching ratios for sgoldstinos decaying to final states involving Higgs bosons and sparticles which have not been discussed in detail so far.

hep-ph↗
arXiv2016

Light Higgsino as the tail of the $μ$-$B_μ$ solution

Gauge mediation predicts 10 TeV or heavier squarks because such a heavy stop is required to explain the observed 125 GeV Higgs boson mass without a large trilinear soft mass term in the minimal supersymmetric standard model. Although such a high scale cannot be searched by the LHC directly, gauge mediation also predicts a hierarchy $μ^2 \ll B_μ$ by a simple and naive solution of the $μ$ problem. We point out that this simple and naive way of generating the $μ$ ($B_μ$) term works in the case of 10 TeV or heavier squarks with a slight breaking of a GUT relation among messenger B-terms (or supersymmetric mass terms). Furthermore, the upper bound on the Higgsino mass is obtained from the observed Higgs boson mass, perturbativity of a relevant coupling, and conditions avoiding tachyonic sneutrinos and stop. It turns out that the light Higgsino of O(100) GeV is a promising signal of gauge mediation.

hep-ph↗
arXiv2016

Low-Scale Gauge Mediation with a 100 TeV Gravitino

We propose a new framework of low-scale gauge-mediated supersymmetry (SUSY) breaking with a gravitino mass of O(100) TeV. The usual 4D gauge mediation models predict a light gravitino and suffer from cosmological problems. In our framework, a heavy gravitino in gauge mediation is realized with a flat extra-dimension, whose compactification scale is around the grand unified theory scale. Superparticle masses of the visible sector from gravity/anomaly mediation are suppressed, and they are purely generated by usual gauge mediation on the visible brane. Importantly, the Higgs Bmu-term vanishes at the leading order, which enables us to obtain the suitable mu-Bmu relation for the electroweak symmetry breaking. We discuss such models considering two possibilities of the SUSY breaking source: 1) Scherk-Schwarz SUSY breaking which we call Scherk-Schwarz Gauge Mediation and 2) gravitational SUSY breaking localized on a hidden brane. In the case 2), the cosmological moduli problem may be relaxed as well.

hep-ph↗
arXiv2015

A New Scheme for NMSSM in Gauge Mediation

We propose a new framework for the next-to-minimal supersymmetric standard model (NMSSM) in gauge mediation, where in general the correct electroweak symmetry breaking (EWSB) is difficult to be explained. The difficulty is caused by the absence of a soft supersymmetry (SUSY) breaking mass for the NMSSM singlet S. In our framework, S is a meson in a hidden QCD. This QCD is responsible for the dynamical SUSY breaking, forming S, and the soft SUSY breaking mass for S, which is a key to explain the correct EWSB: all the ingredients for successful phenomenology originate from the common dynamics. From the requirement of the successful EWSB, the low-scale SUSY breaking around 100-1000 TeV is predicted. This is favored to avoid the large fine-tuning.

hep-ph↗
arXiv2014

Partially Composite Dark Matter

In a class of theories where the Higgs field emerges as a pseudo Nambu-Goldstone boson, it is often assumed that interactions to generate the top Yukawa coupling provide the Higgs potential as well. Such a scenario generically requires a little cancellation in the leading contribution to the Higgs potential, and the electroweak scale is generated by the balance between the leading and the subleading contributions. We, instead, consider the possibility that the contribution from the dark matter particle balances against that from the top quark. The thermal relic of the new particle explains the abundance of dark matter in a consistent region of the parameter space, and the direct detection is found to be promising.

hep-ph↗
arXiv2014

Multi-hadron final states in RPV supersymmetric models with extra matters

The gluino mass has been constrained by various search channels at the LHC experiments and the recent analyses are even sensitive to the cases where gluinos decay to quarks at the end of the decay chains through the baryonic RPV operator. We argue that introduction of extra matters, which is partly motivated by cancelling anomalies of discrete R symmetry, may help to relax the gluino mass limit when the RPV hadronic gluino decays are considered. In the scenarios where the extra matter states appear in the gluino decay chains, the number of decay products increases and each jet becomes soft, making it difficult to distinguish the signal from backgrounds. We investigate the sensitivity of existing analyses to such scenarios and demonstrate that the gluino mass limit can be relaxed if the mass spectrum reconciles the sensitivities of high $p_T$ jet searches and large jet multiplicity searches.

hep-ph↗
arXiv2014

Composite Higgsino

Several supersymmetric models in which there is a (partially) composite Higgs boson arising from (coupled to) a strong sector have been proposed. Such strong dynamics would help to cause the electroweak symmetry breaking naturally. In this paper, we focus on the compositeness of the Higgsinos in such models. We show that such a Higgsino compositeness can induce the characteristic decay branching fraction of the neutralinos. In such scenarios, the decay branching fraction of the second lightest neutral Higgsino into the lightest neutral Higgsino with photon can be large due to a dipole interaction. We also discuss the Higgsino dark matter feature. The annihilation cross section into gamma Z can be large.

hep-ph↗
arXiv2013

The 130 GeV gamma-ray line and generic dark matter model building constraints from continuum gamma rays, radio and antiproton data

An analysis of the Fermi gamma ray space telescope data has recently revealed a resolved gamma-ray feature close to the galactic center which is consistent with monochromatic photons at an energy of about 130 GeV. If interpreted in terms of dark matter (DM) annihilating into γγ(γZ, γh), this would correspond to a DM particle mass of roughly 130 GeV (145 GeV, 155 GeV). The rate for these loop-suppressed processes, however, is larger than typically expected for thermally produced DM. Correspondingly, one would generically expect even larger tree level production rates of standard model fermions or gauge bosons. Here, we quantify this expectation in a rather model-independent way by relating the tree level and loop amplitudes with the help of the optical theorem. As an application, we consider bounds from continuum gamma rays, radio and antiproton data on the tree level amplitudes and translate them into constraints on the loop amplitudes. We find that, independently of the DM production mechanism, any DM model aiming at explaining the line signal in terms of charged standard model particles running in the loop is in rather strong tension with at least one of these constraints, with the exception of loops dominated by top quarks. We stress that attempts to explain the 130 GeV feature with internal bremsstrahlung do not suffer from such difficulties.

hep-ph↗
arXiv2013

Can R-parity violation hide vanilla supersymmetry at the LHC?

Current experimental constraints on a large parameter space in supersymmetric models rely on the large missing energy signature. This is usually provided by the lightest neutralino which stability is ensured by the R-parity. However, if the R-parity is violated, the lightest neutralino decays into the standard model particles and the missing energy cut is not efficient anymore. In particular, the UDD type R-parity violation induces the neutralino decay to three quarks which potentially leads to the most difficult signal to be searched at hadron colliders. In this paper, we study the constraints on the R-parity violating supersymmetric model using a same-sign dilepton and a multijet signatures. We show that the gluino and squarks lighter than a TeV are already excluded in constrained minimal supersymmetric standard model with R-parity violation if their masses are approximately equal. We also analyze constraints in a simplified model with R-parity violation. We compare how R-parity violation changes some of the observables typically used to distinguish a supersymmetric signal from standard model backgrounds.

hep-ph↗
arXiv2012

Natural supersymmetric spectrum in mirage mediation

Current results of LHC experiments exclude large area of light new particle region, namely natural parameter space, in supersymmetric extension models. One of the possibilities for achieving the correct electroweak symmetry breaking naturally is low scale messenger scenario. Actually, the next-to-minimal supersymmetric standard model with TeV scale mirage mediation realizes the natural electroweak symmetry breaking with various mass spectra. In this paper, we show the possible mass spectrum in the scenario, e.g. degenerate and/or hierarchical mass spectrum, and discuss these features.

hep-ph↗
arXiv2012

Comprehensive Analysis on the Light Higgs Boson Scenario

Comprehensive analysis on the light Higgs scenario of the minimal supersymmetric standard model is performed in the framework of the non-universal Higgs mass model (NUHM). The NUHM is known to be the simplest framework realizing the light Higgs scenario with the unifications of gaugino and sfermion masses at the scale of grand unified theory being consistent. All important constraints from collider experiments, flavor-changing processes, and cosmological observations are considered in order to clarify the allowed region of the model parameter space, where the Markov Chain Monte Carlo method is used to obtain the region. We show that the region is excluded by current LHC results for the SUSY particle searches. We discuss possible extensions to save the LHS. Even with such extensions, the measurement of B_s to mu^+ mu^- would enable us to test the LHS in the near future.

hep-ph↗
arXiv2012

Little Higgs with T-parity measurements at the ILC

The Littlest Higgs with T-parity Model (LHT) is one of the attractive candidates of physics beyond the Standard Model. In this study we focus on heavy gauge bosons and heavy leptons that LHT imposes, which are detectable at ILC. The mass and couplings of these particles possess important information of the model's mass generation mechanism and how they interact with other particles. Precision measurement will be essential among verifying the model. We will address the measurement accuracy of Little Higgs particle masses, couplings and model parameters at ILC.

hep-ph↗
arXiv2012

Indirect dark matter searches as a probe of degenerate particle spectra

We consider the possibility that the cosmological dark matter consists of particles very close in mass to new colored particles below the TeV scale. While such a scenario is inherently difficult to directly confirm at colliders, we find that indirect dark matter searches may be a powerful alternative. In particular, we show that in this case dark matter annihilation to quark-quark-gluon final states can give rise to significant antiproton (but also gamma-ray) fluxes, and compare the resulting constraints to bounds from direct searches at LEP, the Tevatron and the LHC. For supersymmetric neutralinos degenerate with squarks, e.g., antiprotons can give rise to more stringent constraints for masses below around 45-80 GeV.

hep-ph↗
arXiv2011

Exploring Supersymmetric Model with Very Light Gravitino at the LHC

The low-scale gauge mediation scenario of supersymmetry breaking predicts very light gravitino, which makes the next lightest supersymmetric particle (NLSP) quasi stable. We study the LHC phenomenology of the case that the NLSP is the stau. When the mass of the gravitino is of the order of 10eV, the decay length of stau is about 0.1--1 mm, so that it decays before reaching the first layer of the inner silicon detector. We show, however, that, with utilizing the impact parameter of tau-jets from the stau decay, it is possible to determine the mass spectrum of sparticles precisely. It is also possible to estimate the lifetime of the stau by observing distribution of the impact parameter.

hep-ph↗
arXiv2011

Focus Point Assisted by Right-Handed Neutrinos

The large hadron collider experiments have now reached the focus point region in which the scalar masses are multi-TeV. We study the parameter region of the focus point scenario which may realize a natural electroweak symmetry breaking avoiding serious fine tuning. We show that the region with a mild tuning of 3-5 % level is expanded by introducing right-handed neutrinos in the framework of the seesaw scenario. We discuss the prediction of the Higgs mass, bounds on the squark and gluino masses, and the relic density of the lightest neutralino in such a parameter region.

hep-ph↗
arXiv2011

Discrimination of New Physics Models with the International Linear Collider

The large hadron collider (LHC) is anticipated to provide signals of new physics at the TeV scale, which are likely to involve production of a WIMP dark matter candidate. The international linear collider (ILC) is to sort out these signals and lead us to some viable model of the new physics at the TeV scale. In this article, we discuss how the ILC can discriminate new physics models, taking the following three examples: the inert Higgs model, the supersymmetric model, and the littlest Higgs model with T-parity. These models predict dark matter particles with different spins, 0, 1/2, and 1, respectively, and hence comprise representative scenarios. Specifically, we focus on the pair production process, e+e- -> chi+chi- -> chi0chi0W+W-, where chi0 and chi+- are the WIMP dark matter and a new charged particle predicted in each of these models. We then evaluate how accurately the properties of these new particles can be determined at the ILC and demonstrate that the ILC is capable of identifying the spin of the new charged particle and discriminating these models.

hep-ph↗
arXiv2011

Non-anomalous Discrete R-symmetry, Extra Matters, and Enhancement of the Lightest SUSY Higgs Mass

We consider low-energy supersymmetric model with non-anomalous discrete R-symmetry. In such a model, to make the R-symmetry non-anomalous, new particles with gauge quantum numbers should be inevitably added to the particle content of the minimal supersymmetric standard model (MSSM). Those new particles may couple to the Higgs boson, resulting in a significant enhancement of the lightest Higgs mass. We show that, in such a model, the lightest Higgs mass can be much larger than the MSSM upper bound; the lightest Higgs mass as large as 140 GeV (or larger) becomes possible.

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