arXiv subjects

Koichi Yoshioka

Publications and source records attributed to Koichi Yoshioka.

At least 19 recordsLinked to original sources

arXiv2025

Two-field inflation from one complex scalar with symmetry breaking

We study two-field inflation derived from a single complex scalar field with a nonzero vacuum expectation value. The dynamics of inflation are governed by two parameters, the vacuum expectation value and the mass parameter of the phase mode, which together give rise to a rich variety of inflationary structures. We classify the possible trajectories of the two inflaton fields and identify the parameter regions consistent with current cosmological observations. Furthermore, we investigate the reheating process through the inflaton decay to right-handed neutrinos and the subsequent generation of lepton number within these regions. Our findings suggest that the presence of multiple scalar degrees of freedom can significantly alter the conditions for successful reheating and leptogenesis.

hep-ph↗

arXiv2025

Multi-Field Effects on Scalar Production in Stars

This paper studies the dynamics of scalar particle production, focusing on the presence of multiple fields and couplings in the medium. The interplay of various fields and couplings can influence the production rate, potentially overshadowing the effect of electrons alone. The plasma mixing, which induces the resonance and screening of scalar processes, is shown to be modified by the in-medium effects depending on the type of processes and field contents. Incorporating these in-medium effects into the analysis of stellar cooling via scalar emission allows for the emergence of various features of multi-field effects given in several types of scalar models.

hep-ph↗

arXiv2023

Stellar cooling limits on light scalar boson revisited

We revisit the stellar cooling limits on the light scalar boson whose coupling to the Standard Model particles is described by its mixing with the Higgs boson. Strong constraints have been obtained from the electron-nucleus bremsstrahlung process and the resonant plasma effect in the medium. We find that the bremsstrahlung contribution from the electron and nucleus scattering is of similar magnitude to the plasma mixing effect including the off-resonant mixing. The constraints on the scalar coupling are found to be about three orders of magnitude weaker than the previous evaluations. For white dwarfs, the stellar cooling constraint is even more suppressed due to the Pauli blocking effect. We obtain limits on the Higgs-scalar mixing angle of $10^{-10}-10^{-9}$ in the region where the scalar mass is lighter than about 10 keV.

hep-ph↗

arXiv2023

Quantum current dissipation in superconducting strings and vortons

In this work, the current stability is discussed for cosmic strings with the bosonic superconductivity. A non-vanishing curvature of string generally induce the quantum instability of the current-carrying particle. Its decay rates are explored for various types of model parameters, curved string shapes, and decay processes. As a cosmological application, the stability is examined for superconducting strings in the string network and also for cosmic vortons by evaluating their cosmological evolution. The zero mode and hence the vorton cannot be stable in various cases, e.g., with a hierarchy between the current-carrying particle mass off the string and the string tension or with sizable couplings of the current-carrying particle to light species such as the Standard Model particles.

hep-ph↗

arXiv2023

Leptonic CP asymmetry and Light flavored scalar

We consider a situation where right-handed neutrinos couple to a light scalar which is possibly a Nambu-Goldstone boson resulting from high-energy symmetry breaking. Its coupling is typically complex-valued and flavor-dependent. In this work, we investigate the possibility of the leptonic asymmetry generation in the Universe from the right-handed neutrino decay to flavorful light scalar. Furthermore a new source of asymmetry generation from a single decay process is pointed out, which is characteristic of the present setting.

hep-ph↗

arXiv2021

Electroweak axion string and superconductivity

We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, called the electroweak axion strings, can exhibit superconductivity without fermionic zero modes. We construct three types of electroweak axion string solutions. Among them, the string with $W$-flux can be lightest in some parameter space, which leads to a stable superconducting cosmic string. We also show that a large electric current can flow along the string due to the Peccei-Quinn scale much higher than the electroweak scale. This large current induces a net attractive force between the axion strings with the same topological charge, which opens a novel possibility that the axion strings form Y-junctions in the early universe.

hep-ph↗

arXiv2021

Non-thermal Production of PNGB Dark Matter and Inflation

A pseudo Nambu-Goldstone boson (pNGB) is a natural candidate of dark matter in that it avoids the severe direct detection bounds. We show in this paper that the pNGB has another different and interesting face with a higher symmetry breaking scale. Such large symmetry breaking is motivated by various physics beyond the standard model. In this case, the pNGB interaction is suppressed due to the Nambu-Goldstone property and the freeze-out production does not work even with sufficiently large portal coupling. We then study the pNGB dark matter relic abundance from the out-of-equilibrium production via feeble Higgs portal coupling. Further, a possibility is pursued the symmetry breaking scalar in the pNGB model plays the role of inflaton. The inflaton and dark matter are unified in a single field and the pNGB production from inflaton decay is inevitable. For these non-thermally produced relic abundance of pNGB dark matter and successful inflation, we find that the dark matter mass should be less than a few GeV in the wide range of the reheating temperature and the inflaton mass.

hep-ph↗

arXiv2020

TeV-scale Majorogenesis

The Majoron, the Nambu-Goldstone boson of lepton number symmetry, is an interesting candidate for dark matter as it deeply connects the dark matter and neutrino physics. In this paper, we consider the Majoron dark matter as pseudo Nambu-Goldstone boson with TeV-scale mass. The heavy Majoron generally has the large decay constant and tiny Yukawa couplings to light right-handed neutrinos which are required by cosmological and astrophysical observations. That makes it difficult to realize the desired amount of the relic abundance of Majoron dark matter. We consider three improved scenarios for the generation of Majoron, dubbed as Majorogenesis, in the early universe and find in all cases the parameter space compatible with the relic abundance and cosmic-ray constraints.

hep-ph↗

arXiv2016

Superspace Gauge Fixing in Yang-Mills Matter Coupled Conformal Supergravity

In $D=4$, $\cal{N}=1$ conformal superspace, the Yang-Mills matter coupled supergravity system is constructed where the Yang-Mills gauge interaction is introduced by extending the superconformal group to include the Kähler isometry group of chiral matter fields. There are two gauge-fixing procedures to get to the component Poincaré supergravity: one via the superconformal component formalism and the other via the Poincaré superspace formalism. These two types of superconformal gauge-fixing conditions are analyzed in detail and their correspondence is clarified.

hep-th↗

arXiv2016

Higgs Boson Mass and Muon g-2 with Strongly Coupled Vector-like Generations

We study the Higgs boson mass and the muon anomalous magnetic moment (the muon $g-2$) in a supersymmetric standard model with vector-like generations. The infrared physics of the model is governed by strong renormalization-group effects of the gauge couplings. That leads to sizable extra Yukawa couplings of Higgs doublets between the second and vector-like generations in both quark and lepton sectors. It is found with this property that there exist wide parameter regions where the Higgs boson mass and the muon $g-2$ are simultaneously explained.

hep-ph↗

arXiv2016

Component versus Superspace Approaches to D=4, N=1 Conformal Supergravity

The superspace formulation of N=1 conformal supergravity in four dimensions is demonstrated to be equivalent to the conventional component field approach based on the superconformal tensor calculus. The detailed correspondence between two approaches is explicitly given for various quantities; superconformal gauge fields, curvatures and curvature constraints, general conformal multiplets and their transformation laws, and so on. In particular, we carefully analyze the curvature constraints leading to the superconformal algebra and also the superconformal gauge fixing leading to Poincare supergravity since they look rather different between two approaches.

hep-th↗

arXiv2012

Runaway, D term and R-symmetry Breaking

We study the D-term effect on runaway directions of the F-term scalar potential. A minimal renormalizable model is presented where supersymmetry is broken without any pseudomoduli. The model is applied to the hidden sector of gauge mediation for spontaneously breaking R symmetry and generating nonvanishing gaugino masses at the one-loop order.

hep-ph↗

arXiv2011

D term and gaugino masses in gauge mediation

We systematically study supersymmetry breaking with non-vanishing F and D terms. We classify the models into two categories and find that a certain class of models necessarily has runaway behavior of scalar potential, while the other needs the Fayet-Iliopoulos term to break supersymmetry. The latter class is useful to have a simple model of gauge mediation where the vacuum is stable everywhere and the gaugino mass is generated at the one-loop order.

hep-ph↗

arXiv2010

Extra dimensions and Seesaw Neutrinos at the International Linear Collider

We study the capability of the international linear collider (ILC) to probe extra dimensions via the seesaw mechanism. In the scenario we study, heavy Kaluza-Klein neutrinos generate tiny neutrino masses and, at the same time, have sizable couplings to the standard-model particles. Consequently, a Kaluza-Klein tower of heavy neutrinos (N) can be produced and studied at the ILC through the process: e+e- -> vN followed by N -> Wl decay. We show that the single lepton plus two-jets final states with large missing energy from this signal process will provide a good opportunity to measure the masses and cross sections of Kaluza-Klein neutrinos up to the third level. Furthermore, the neutrino oscillation parameters can be extracted from the flavor dependence of the lowest-mode signals, which give us information about the origin of low-energy neutrino masses.

hep-ph↗

arXiv2010

Deep Correlation Between Cosmic-Ray Anomaly and Neutrino Masses

The positron anomaly recently reported by the cosmic-ray measurements suggests that, if explained by the decay of dark matter particle, the decay source is closely linked up with the leptonic sector of the standard model. It is observed that, with a simple dimensional analysis, the lifetime of dark matter for the anomaly is expressed by the energy scale of neutrino masses. We present two scenarios in which these two matter at issue (the dark matter width and the tiny neutrino masses) stem from a single operator involving a gauge-singlet scalar field.

hep-ph↗

arXiv2010

Universally Leptophilic Dark Matter From Non-Abelian Discrete Symmetry

The positron anomaly recently reported by the cosmic-ray measurements can be explained by the decaying dark matter scenario, where it decays mainly into leptons with the lifetime of O(10^26) second. When the dark matter is a fermionic particle, the lifetime of this order is known to be obtained by a dimension 6 operator suppressed by the unification scale 10^16 GeV, while such decay operators do not necessarily involve only leptons. In addition, the scenario would be spoiled if there exist lower-dimensional operators inducing the dark matter decay. We show in this letter that a single non-Abelian discrete symmetry such as A_4 is possible to prohibit all such harmful (non-leptonically coupled and lower-dimensional) operators. Moreover, the dark matter decays into charged leptons in a flavor-blind fashion due to the non-Abelian flavor symmetry, which results in perfect agreements not only with the PAMELA data but also with the latest Fermi-LAT data reported very recently. We also discuss some relevance between the discrete symmetry and neutrino physics.

hep-ph↗

arXiv2010

Seesaw in the bulk

A five-dimensional seesaw framework is analyzed with the lepton-number-violating propagator of bulk right-handed neutrinos. That can bypass summing up the effects of heavy Majorana particles whose masses and wavefunctions are not exactly known. The propagator method makes it easier to evaluate the seesaw-induced neutrino mass for various boundary conditions of bulk neutrinos and in a general background geometry, including the warped extra dimension. It is also found that the higher-dimensional seesaw gives a natural framework for the inverse seesaw suppression of low-energy neutrino masses.

hep-ph↗

arXiv2010

Seesaw Neutrino Signals at the Large Hadron Collider

We discuss the scenario with gauge singlet fermions (right-handed neutrinos) accessible at the energy of the Large Hadron Collider. The singlet fermions generate tiny neutrino masses via the seesaw mechanism and also have sizable couplings to the standard-model particles. We demonstrate that these two facts, which are naively not satisfied simultaneously, are reconciled in the five-dimensional framework in various fashions, which make the seesaw mechanism observable. The collider signal of tri-lepton final states with transverse missing energy is investigated for two explicit examples of the observable seesaw, taking account of three types of neutrino mass spectrum and the constraint from lepton flavor violation. We find by showing the significance of signal discovery that the collider experiment has a potential to find signals of extra dimensions and the origin of small neutrino masses.

hep-ph↗