Minoru Nagai

Non-perturbative effect on thermal relic abundance of dark matter

Abstract We point out that thermal relic abundance of the dark matter is strongly altered by a non-perturbative effect called the Sommerfeld enhancement, when constituent particles of the dark matter are non-singlet under the SU(2)L gauge interaction and much heavier than the weak gauge bosons. Typical candidates for such dark matter particles are the heavy wino- and higgsino-like neutralinos. We investigate the non-perturbative effect on the relic abundance of dark matter for the wino-like neutralino as an example. We show that its thermal abundance is reduced by 50% compared to the perturbative result. The wino-like neutralino mass consistent with the observed dark matter abundance turns out to be 2.7 TeV ≲ m ≲ 3.0 TeV .

Flavor effects on the electric dipole moments in supersymmetric theories: A beyond leading order analysis

The Standard Model predictions for the hadronic and leptonic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics effects. Especially, within supersymmetric frameworks with flavor-violating soft terms large and potentially visible effects to the EDMs are typically expected. In this work, we systematically evaluate the predictions for the EDMs at the beyond-leading-order (BLO). In fact, we show that BLO contributions to the EDMs dominate over the leading-order (LO) effects in large regions of the supersymmetric parameter space. Hence, their inclusion in the evaluation of the EDMs is unavoidable. As an example, we show the relevance of BLO effects to the EDMs for a SUSY SU(5) model with right-handed neutrinos.

Probing Supersymmetric Model with Heavy Sfermions Using Leptonic Flavor and CP Violations

Abstract We study leptonic flavor and CP violating observables in supersymmetric (SUSY) models with heavy sfermions, which is motivated by the recent results of the LHC experiments (i.e., the discovery of the Higgs-like boson with the mass of about 126 GeV and the negative searches for the superparticles). Even if the sfermion masses are of O ( 10 – 100 TeV ) , signals may be within the reach of future leptonic flavor and CP violation experiments assuming that the off-diagonal elements of the sfermion mass matrices are unsuppressed compared to the diagonal ones. We also consider the SUSY contribution to the K 0 - K ¯ 0 mixing parameters; we show that the leptonic observables can become as powerful as those in K 0 - K ¯ 0 mixing to constrain SUSY models.

Waiting for μ → eγ from the MEG experiment

The Standard Model (SM) predictions for the lepton flavor-violating (LFV) processes like μ → eγ are well far from any realistic experimental resolution, thus, the appearance of μ → eγ at the running MEG experiment would unambiguously point towards a New Physics (NP) signal. In this article, we discuss the phenomenological implications in case of observation/improved upper bound on μ → eγ at the running MEG experiment for supersymmetric (SUSY) scenarios with a see-saw mechanism accounting for the neutrino masses. We outline the role of related observables to μ → eγ in shedding light on the nature of the SUSY LFV sources providing useful tools i) to reconstruct some fundamental parameters of the neutrino physics and ii) to test whether an underlying SUSY Grand Unified Theory (GUT) is at work. The perspectives for the detection of LFV signals in τ decays are also discussed.The Standard Model (SM) predictions for the lepton flavor-violating (LFV) processes like mu->eg are well far from any realistic experimental resolution, thus, the appearance of m->eg at the running MEG experiment would unambiguously point towards a New Physics (NP) signal. In this article, we discuss the phenomenological implications in case of observation/improved upper bound on m->eg at the running MEG experiment for supersymmetric (SUSY) scenarios with a see-saw mechanism accounting for the neutrino masses. We outline the role of related observables to m->eg in shedding light on the nature of the SUSY LFV sources providing useful tools i) to reconstruct some fundamental parameters of the neutrino physics and ii) to test whether an underlying SUSY Grand Unified Theory (GUT) is at work. The perspectives for the detection of LFV signals in tau decays are also discussed.

New two-loop contributions to hadronic EDMs in the MSSM

Abstract Flavor-changing terms with CP-violating phases in the quark sector may contribute to the hadronic electric dipole moments (EDMs). However, within the Standard Model (SM), the source of CP violation comes from the unique CKM phase, and it turns out that the EDMs are strongly suppressed. This implies that the EDMs are very sensitive to non-minimal flavor violation structures of theories beyond the SM. In this Letter, we discuss the quark EDMs and CEDMs (chromoelectric dipole moments) in the MSSM with general flavor-changing terms in the squark mass matrices. In particular, the charged-Higgs mediated contributions to the down-quark EDM and CEDM are evaluated at two-loop level. We point out that these two-loop contributions may dominate over the one-loop induced gluino or higgsino contributions even when the squark and gluino masses are around few TeV and tan β is moderate.

Non-thermal production of Wino dark matter via the decay of long-lived particles

A bstractWe consider supersymmetric models in which the neutral Wino is the lightest superparticle (LSP), and study the possibility that non-thermally produced Wino plays the role of dark matter. The thermal relic density of Wino is smaller than the present mass density of dark matter if

Hadronic EDMs in SUSY SU(5) GUTs with right-handed neutrinos

{m_{{\widetilde{W}}}}

The anatomy of neutral scalars with FCNCs in the flavour precision era

≲ 2.9 TeV; however, even with smaller Wino mass, the Wino can be the dominant component of dark matter if it is non-thermally produced by the decay of a long-lived particle. In order to study such a possibility in detail, we perform a precise calculation of the present mass density of Wino produced by the decay of a long- lived particle, taking account of the following effects: (i) coannihilation among charged and neutral Winos, and (ii) Sommerfeld effect on the pair annihilation cross section of Winos. We consider several well-motivated cases where the long-lived particle corresponds to cosmological moduli fields, gravitino, or axino, and discuss the implication of the Wino LSP for these cases.

Electric dipole moments from flavor-changing supersymmetric soft terms

Abstract We discuss hadronic EDM constraints on the neutrino sector in the SUSY SU(5) GUT with the right-handed neutrinos. The hadronic EDMs are sensitive to the right-handed down-type squark mixings, especially between the second and third generations and between the first and third ones, compared with the other low-energy hadronic observables, and the flavor mixings are induced by the neutrino Yukawa interaction. The current experimental bound of the neutron EDM may imply that the right-handed tau neutrino mass is smaller than about 10 14 GeV in the minimal supergravity scenario, and it may be improved furthermore in future experiments, such as the deuteron EDM measurement.

Footprints of SUSY GUTs in flavour physics

A bstractIn many extensions of the Standard Model (SM) flavour changing neutral current (FCNC) processes can be mediated by tree-level heavy neutral scalars and/or pseudo-scalars H0(A0). This generally introduces new sources of flavour violation and CP violation as well as left-handed (LH) and right-handed (RH) scalar (1 ∓ γ5) currents. These new physics (NP) contributions imply a pattern of deviations from SM expectations for FCNC processes that depends only on the couplings of H0(A0) to fermions and on their masses. In situations in which a single H0 or A0 dominates NP contributions stringent correlations between ΔF = 2 and ΔF = 1 observables exist. Anticipating the Flavour Precision Era (FPE) ahead of us we illustrate this by searching for allowed oases in the landscape of a given model assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze ΔF = 2 observables in