arXiv subjects

Tomohiro Abe

Publications and source records attributed to Tomohiro Abe.

At least 19 recordsLinked to original sources

arXiv2026

Sommerfeld Enhancement in Spin-1 Electroweak Dark Matter

We study a renormalizable spin-1 electroweakly interacting dark matter (DM) model in which the DM particle is the neutral component of a $Z_2$-odd $\mathrm{SU(2)}_L$ triplet vector boson. The model predicts an additional $Z_2$-even heavy vector triplet, $W'^{\pm}$ and $Z'$, which is generically heavier than the DM particle and whose mass is closely related to the DM mass. Taking into account the Sommerfeld enhancement due to long-range electroweak interactions, we evaluate the thermal relic abundance of the spin-1 DM. We find that the observed relic abundance is reproduced through the freeze-out mechanism for DM masses ($m_V$) in the range $3.6~\mathrm{TeV} \lesssim m_V \lesssim 9.2~\mathrm{TeV}$ within a perturbative regime. A heavier DM mass is favored when the heavy vector boson mass approaches the DM mass, since annihilation processes into a heavy vector boson and a Standard Model particle significantly enhance the effective annihilation cross section. This behavior is distinctive from spin-0 and spin-$1/2$ electroweak DM scenarios, which typically predict a DM mass around $3~\mathrm{TeV}$. We further investigate indirect detection prospects and find that the Cherenkov Telescope Array Observatory (CTAO) will probe the entire viable parameter region. In particular, for $m_V \gtrsim 7.5~\mathrm{TeV}$, the model predicts a characteristic double-peak gamma-ray signature: one peak arising from the unresolved $\gamma\gamma$ and $Z\gamma$ channels, and the other from the $Z'\gamma$ annihilation channel.

hep-ph↗

arXiv2026

Sommerfeld enhancement from unstable final-state particles in dark matter annihilation

We study the Sommerfeld enhancement of the annihilation cross section of dark matter into heavier unstable particles. In this process, the annihilation products become non-relativistic near the kinematical threshold. If they experience long-range interactions with each other, their wave function is distorted from a plane wave, and the annihilation cross section can be significantly enhanced. When evaluating the Sommerfeld enhancement from the long-range interactions between the annihilation products, the decay of the products needs to be taken into account. We treat this issue by including the decay width in the Schr\"odinger equations of the two-body wave function of the annihilation products. We find that bound states of the annihilation products with a narrow decay width enhance the annihilation cross section through a resonant effect. At the same time, this formulation automatically includes the annihilation process with off-shell final state particles, which is relevant for a wide decay width. We show that the resonant effect significantly affects the prediction of the dark matter relic abundance.

hep-ph↗

arXiv2024

Tiny yet detectable WIMP-nucleon scattering cross sections in a pseudo-Nambu-Goldstone dark matter model

We investigate a pseudo-Nambu-Goldstone (pNG) dark matter (DM) model based on a gauged $SU(2)_x$ and a global $SU(2)_g$ symmetries. These symmetries are spontaneously broken to a global $U(1)_D$ symmetry by a vacuum expectation value of an $SU(2)_x \times SU(2)_g$ bi-fundamental scalar field. The global $SU(2)_g$ symmetry is also softly broken to a global $U(1)_D$ symmetry. Under the setup, a complex pNG boson arises. It is stabilized by $U(1)_D$ and is a DM candidate. Its scattering cross section off a nucleon is highly suppressed by small momentum transfer and thus evades the stringent constraints from DM direct detection experiments. Assuming all the couplings in the dark sector are real, a discrete symmetry arises. Consequently, in addition to the pNG DM, the lighter one of an $SU(2)_x$ gauge boson $V^0$ and a CP-odd scalar boson $a_0$ from the bi-fundamental scalar field can also serve as a DM candidate. Therefore, the model provides two-component DM scenarios. We find that the relic abundance of the DM candidates explains the measured value of the DM energy density. We also find that the pNG DM is the dominant DM component in large regions of the parameter space. In contrast to the pNG DM, both $V^0$ and $a_0$ scatter off a nucleon, and their scattering cross sections are not suppressed. However, their scattering event rates are suppressed by their number densities. Thus, the scattering cross section is effectively reduced. We show that the effective WIMP-nucleon scattering cross sections in the two-component scenarios are smaller than the current upper bounds and above the neutrino fog.

hep-ph↗

arXiv2024

Composite Dark Matter with Forbidden Annihilation

A dark matter model based on QCD-like $SU(N_c)$ gauge theory with electroweakly interacting dark quarks is discussed. Assuming the dark quark mass $m$ is smaller than the dynamical scale $\Lambda_d \sim 4\pi f_d$, the main component of the dark matter is the lightest $G$-parity odd dark pion associated with chiral symmetry breaking in the dark sector. We show that nonzero dark quark mass induces the universal mass contribution to both $G$-parity odd and even pions, and their masses tend to be degenerate. As a result, dark pion annihilation into heavier $G$-parity even dark pion also affects the dark matter relic abundance. Thus, our setup naturally accommodates forbidden dark matter scenario and realizes heavy dark matter whose mass is ${\cal O}(1$-$100)~{\rm TeV}$, which is different from conventional electroweakly interacting dark matter such as minimal dark matter. We also discuss CP-violation from $\theta$-term in the dark gauge sector and find that the predicted size of electron electric dipole moment can be as large as $\sim 10^{-32}~e~{\rm cm}$.

hep-ph↗

arXiv2024

A model of pseudo-Nambu-Goldstone dark matter with two complex scalars

Pseudo-Nambu-Goldstone (pNG) dark matter (DM) is a promising DM candidate and able to explain the measured DM abundance by the thermal freeze-out mechanism evading the stringent bound from DM direct detection experiments. We propose a new model providing a pNG DM by introducing two Standard-Model-singlet complex scalars with the same charges of a dark $U(1)$ gauge symmetry. They are also charged under a $U(1)$ global symmetry corresponding to their relative phase rotations, which is explicitly broken by a soft-breaking term in the scalar potential. The both $U(1)$ symmetries are spontaneously broken by their vacuum expectation values, giving rise to one real pNG boson. We also introduce a discrete $\mathbb{Z}_2$ symmetry exchanging the two scalars to stabilize the pNG boson as DM. It is shown that this model reproduces the DM abundance consistently with the current bound from the direct detection experiments. The model has a gauge kinetic mixing between the dark and $U(1)_Y$ gauge fields, which allows the dark gauge boson to decay even with a relatively light mass and prevents it from being an additional DM component. The Landau pole is avoided thanks to the small gauge coupling constant. In addition, a DM pair dominantly annihilates into a pair of the dark gauge bosons if the gauge boson mass is lighter than the DM mass, and thus its cross section has significantly different parameter dependence from other pNG DM models. We also calculate the DM-nucleon scattering cross section at the loop level. It turns out that it is necessary to probe region covered by the neutrino fog in order to test this model.

hep-ph↗

arXiv2023

Gravitational Wave Signatures of a Chiral Fermion Dark Matter Model

Theories in which the dark matter (DM) candidate is a fermion transforming chirally under a gauge symmetry are attractive, as the gauge symmetry would protect the DM mass. In such theories, the universe would have undergone a phase transition at early times that generated the DM mass upon spontaneous breaking of the gauge symmetry. In this paper, we explore the gravitational wave signals of a simple such theory based on an $\mathrm{SU}(2)_\mathrm{D}$ dark sector with a dark isospin-$3/2$ fermion serving as the DM candidate. This is arguably the simplest chiral theory possible. The scalar sector consists of a dark isospin-$3$ multiplet which breaks the $\mathrm{SU}(2)_\mathrm{D}$ gauge symmetry and also generates the DM mass. We construct the full thermal potential of the model and identify regions of parameter space which lead to detectable gravitational wave signals, arising from a strong first-order $\mathrm{SU}(2)_\mathrm{D}$ phase transition, in various planned space-based interferometers, while also being consistent with dark matter relic abundance. Bulk of the parameter space exhibiting detectable gravitational wave signals in the model also has large WIMP-nucleon scattering cross sections, $\sigma_{\rm SI}$, which could be probed in upcoming direct detection experiments.

hep-ph↗

arXiv2023

Gravitational waves from first-order phase transition in an electroweakly interacting vector dark matter model

We discuss gravitational waves in an electroweakly interacting vector dark matter model. In the model, the electroweak gauge symmetry is extended to SU(2)$_0 \times$ SU(2)$_1 \times$SU(2)$_2 \times$ U(1)$_Y$ and spontaneously broken into SU(2)$_L \times$ U(1)$_Y$ at TeV scale. The model has an exchange symmetry between SU(2)$_0$ and SU(2)$_2$. This symmetry stabilizes some massive vector bosons associated with the spontaneous symmetry breaking described above, and an electrically neutral one is a dark matter candidate. In the previous study, it was found that the gauge couplings of SU(2)$_0$ and SU(2)$_1$ are relatively large to explain the measured value of the dark matter energy density via the freeze-out mechanism. With the large gauge couplings, the gauge bosons potentially have a sizable effect on the scalar potential. In this paper, we focus on the phase transition of SU(2)$_0 \times$ SU(2)$_1 \times$ SU(2)$_2 \to$ SU(2)$_L$. We calculate the effective potential at finite temperature and find that the phase transition is first-order and strong in a wide range of the parameter space. The strong first-order phase transition generates gravitational waves. We calculate the gravitational wave spectrum and find that it is possible to detect the gravitational waves predicted in the model by future space-based gravitational wave interferometers. We explore the regions of the parameter space probed by the gravitational wave detection. We find that the gravitational wave detection can probe the region where the mass of $h'$, a CP-even scalar in the model, is a few TeV.

hep-ph↗

arXiv2023

A model of pseudo-Nambu-Goldstone dark matter from a softly broken $SU(2)$ global symmetry with a $U(1)$ gauge symmetry

A model of the pseudo-Nambu-Goldstone (pNG) dark matter (DM) is proposed. We assume that there is an $SU(2)_g$ global symmetry and a $U(1)_X$ gauge symmetry in the dark sector, and they are spontaneously broken into a $U(1)_D$ global symmetry after a scalar field develops a vacuum expectation value. We add a soft symmetry breaking term that breaks the $SU(2)_g$ global symmetry into the $U(1)_g$ global symmetry explicitly. Our model predicts a stable complex pNG particle under the $U(1)_D$ global symmetry. One of the virtues of the pNG DM models is that the models can explain the current null results in the direct detection experiments. The small momentum transfer suppresses the scattering amplitudes thanks to the low energy behavior of the Nambu-Goldstone boson. In our model, the soft symmetry breaking term is uniquely determined. This is the advantage of our model to some earlier works in which some soft symmetry breaking terms cannot be forbidden but are simply assumed to be absent to avoid the constraints from the direct detection experiments. We calculate the thermal relic abundance of the pNG DM and find that model can explain the measured value of the DM energy density under some constraints from the perturbative unitarity.

hep-ph↗

arXiv2021

Gamma-ray line from electroweakly interacting non-abelian spin-1 dark matter

We study gamma-ray line signatures from electroweakly interacting non-abelian spin-1 dark matter (DM). In this model, $Z_2$-odd spin-1 particles including a DM candidate have the SU(2)$_L$ triplet-like features, and the Sommerfeld enhancement is relevant in the annihilation processes. We derive the annihilation cross sections contributing to the photon emission and compare with the SU(2)$_L$ triplet fermions, such as Wino DM in the supersymmetric Standard Model. The Sommerfeld enhancement factor is approximately the same in both systems, while our spin-1 DM predicts the larger annihilation cross sections into $γγ/ Z γ$ modes than those of the Wino by $\frac{38}{9}$. This is because a spin-1 DM pair forms not only $J=0$ but also $J=2$ partial wave states where $J$ denotes the total spin angular momentum. Our spin-1 DM also has a new annihilation mode into $Z_2$-even extra heavy vector and photon, $Z' γ$. For this mode, the photon energy depends on the masses of DM and the heavy vector, and thus we have a chance to probe the mass spectrum. The latest gamma-ray line search in the Galactic Center region gives a strong constraint on our spin-$1$ DM. We can probe the DM mass for $\lesssim 25.3~$TeV by the Cherenkov Telescope Array experiment even if we assume a conservative DM density profile.

hep-ph↗

arXiv2021

Early kinetic decoupling and a pseudo-Nambu-Goldstone dark matter model

We study the early kinetic decoupling effect in a pseudo-Nambu-Goldstone (pNG) dark matter (DM) model. The pNG DM scattering processes with particles in the thermal bath in the early Universe are suppressed by the small momentum transfer. As a result, kinetic equilibrium is not maintained, and the temperature of DM is different from the temperature of the thermal bath at the freeze-out era. This temperature difference affects the thermal relic abundance of DM. We investigate the early kinetic decoupling in the Higgs resonance region, 50 GeV $\lesssim m_χ\lesssim m_h/2$, where $m_χ$ is the mass of the DM, and $m_h/2 \simeq$ 62.5 GeV. We find that the DM-Higgs coupling determined to obtain the measured value of the DM energy density is underestimated in the literature. The enhancement in the coupling leads larger value of the Higgs invisible decay rate. It enlarges the capability to discover the DM signals from the decay of the Higgs bosons at collider experiments.

hep-ph↗

arXiv2021

Atomic Form Factors and Inverse Primakoff Scattering of Axion

We reexamine the inverse Primakoff scattering of axions, whose scattering cross section depends on the distribution of electrons in target atoms. We evaluate it using a form factor computed with a relativistic Hartree-Fock wave function and compare it with the previous results obtained with those based on the screened Coulomb potential for the electrostatic field in the atom. We take xenon as an example for the target atom and show that the scattering cross section was overestimated by more than an order of magnitude for axions with $\lesssim O(10)$ keV energies, like solar axions. It is also found that inelastic scattering processes, in which the final state contains an excited or ionized atom, can be comparable or even be dominant when the size of momentum transfer is $\lesssim 1$ keV. For more energetic axions, on the other hand, the total scattering cross section is found to be well approximated by a simple expression and has little dependence on the atomic structure. As an application of this result, we consider supernova axions, whose energy is 10-100 MeV, and show that $O(1)$ inverse Primakoff events are expected for axions from a nearby supernova in the future neutrino experiments, which may warrant a more detailed study on the search strategy of this process.

hep-ph↗

arXiv2021

Simple Theory of Chiral Fermion Dark Matter

We propose a theory of chiral fermion dark matter (DM) with an isospin-3/2 fermion of a dark sector $SU(2)_D$ gauge symmetry, which is arguably the simplest chiral theory. An isospin-3 scalar breaks $SU(2)_D$ down to a discrete non-Abelian group $T'$ and generates the DM mass. The $SU(2)_D$ gauge symmetry protects the DM mass and guarantees its stability. We derive consistency conditions for the theory and study its DM phenomenology. In some regions of parameters of the theory a two-component DM scenario is realized, consisting of a fermion and a boson, with the boson being the lightest $T'$ nonsinglet field. In the case of single component fermionic DM, we find that internal consistency of the theory, perturbativity arguments, and the observed relic abundance limit the DM mass to be less than $280$ GeV, except when $s$-channel resonance regions are open for annihilation. For a significant part of the parameter space, the theory can be tested in DM direct detection signals at the LZ and XENONnT experiments.

hep-ph↗

arXiv2020

Ferroelectricity of Dion-Jacobson layered perovskites CsNdNb$_2$O$_7$ and RbNdNb$_2$O$_7$

Crystallography and dielectric properties in Dion-Jacobson layered perovskites, CsNdNb$_2$O$_7$ and RbNdNb$_2$O$_7$, have been examined in dense polycrystalline samples, and polarization hysteresis loops that substantiate ferroelectricity have been observed at room temperature. The theoretical mechanism for the spontaneous polarization, "hybrid improper ferroelectric mechanism,'' induced by a combination of two types of non-polar octahedral rotations, is confirmed in these two phases. Our samples show remanent polarizations of 2-3 $μ$C/cm$^2$, which are much larger than those obtained in polycrystalline samples with the hybrid improper ferroelectricity reported so far. A dielectric constant in CsNdNb$_2$O$_7$ exhibits an anomaly at 625 K, corresponding to the ferroelectric transition, as previously revealed by x-ray and neutron diffractometry. No dielectric anomaly is observed for RbNdNb$_2$O$_7$ throughout the temperature range studied here ($\leq$ 773 K), which is consistent with the previous diffractometry showing the persistence of polar $I2cm$ symmetry up to 790 K.

cond-mat.mtrl-sci↗

arXiv2020

A model of electroweakly interacting non-abelian vector dark matter

We propose an electroweakly interacting spin-1 dark matter (DM) model. The electroweak gauge symmetry, SU(2)$_L\times$U(1)$_Y$, is extended into SU(2)$_0\times$SU(2)$_1 \times $SU(2)$_2 \times$U(1)$_Y$. A discrete symmetry exchanging SU(2)$_0$ and SU(2)$_2$ is imposed. This discrete symmetry stabilizes the DM candidate. The spin-1 DM particle ($V^0)$ and its SU(2)$_L$ partners ($V^\pm$) interact with the Standard Model (SM) electroweak gauge bosons without any suppression factors. Consequently, pairs of DM particles efficiently annihilate into the SM particles in the early universe, and the measured value of the DM energy density is easily realized by the thermal freeze-out mechanism. The model also predicts a heavy vector triplet ($W'^\pm$ and $Z'$) in the visible sector. They contribute to the DM annihilation processes. The mass ratio of $Z'$ and $V^0$ determines values of various couplings, and constraints on $W'$ and $Z'$ restrict regions of the parameter space that are viable for DM physics. We investigate the constraints from perturbative unitarity of scalar and gauge couplings, the Higgs signal strength, $W'$ search at the LHC, and DM direct detection experiments. It is found that the relic abundance of $V^0$ explains the right amount of the DM energy density for 3 TeV $\lesssim m_{V^0} \lesssim$ 19 TeV.

hep-ph↗

arXiv2020

The effect of the early kinetic decoupling in a fermionic dark matter model

We study the effect of the early kinetic decoupling in a model of fermionic dark matter (DM) that interacts with the standard model particles only by exchanging the Higgs boson. There are two DM-Higgs couplings, namely CP-conserving and CP-violating couplings. If the mass of the DM is slightly below half of the Higgs boson mass, then the couplings are suppressed to obtain the measured value of the DM energy density by the freeze-out mechanism. In addition, the scattering processes of DM off particles in the thermal bath are suppressed by the small momentum transfer if the CP-violating DM-Higgs coupling is larger than the CP-conserving one. Due to the suppression, the temperature of the DM can differ from the temperature of the thermal bath. By solving coupled equations for the number density and temperature of the DM, we calculate the DM-Higgs couplings that reproduce the right amount of the DM relic abundance. We find that the couplings have to be larger than the one obtained without taking into account the difference in the temperatures. A consequence of the enhancement of the DM-Higgs couplings is the enhancement of the Higgs invisible decay branching ratio. The enhancement is testable at current and future collider experiments.

hep-ph↗

arXiv2020

Maximum value of the spin-independent cross section in the THDM+a

We investigate the maximum value of the spin-independent cross section ($σ_\text{SI}$) in a dark matter (DM) model called the two-Higgs doublet model + a (THDM+a). This model can explain the measured value of the DM energy density by the freeze-out mechanism. Also, $σ_\text{SI}$ is suppressed by the momentum transfer at the tree level, and loop diagrams give the leading contribution to it. The model prediction of $σ_\text{SI}$ highly depends on values of $c_1$ and $c_2$ that are the quartic couplings between the gauge singlet CP-odd state ($a_0$) and Higgs doublet fields ($H_1$ and $H_2$), $c_1 a_0^2 H_1^\dagger H_1$ and $c_2 a_0^2 H_2^\dagger H_2$. We discuss the upper and lower bounds on $c_1$ and $c_2$ by studying the stability of the electroweak vacuum, the condition for the potential bounded from the below, and the perturbative unitarity. We find that the condition for the stability of the electroweak vacuum gives upper bounds on $c_1$ and $c_2$. The condition for the potential to be bounded from below gives lower bounds on $c_1$ and $c_2$. It also constrains the mixing angle between the two CP-odd states. The perturbative unitarity bound gives the upper bound on the Yukawa coupling between the dark matter and $a_0$ and the quartic coupling of $a_0$. Under these theoretical constraints, we find that the maximum value of the $σ_\text{SI}$ is $\sim 5\times 10^{-47}$ cm$^2$ for $m_A = $ 600 GeV, and the LZ and XENONnT experiments can see the DM signal predicted in this model near future.

hep-ph↗

arXiv2019

Indirect Studies of Electroweakly Interacting Particles at 100 TeV Hadron Colliders

There are many extensions of the standard model that predict the existence of electroweakly interacting massive particles (EWIMPs), in particular in the context of the dark matter. In this paper, we provide a way for indirectly studying EWIMPs through the precise study of the pair production processes of charged leptons or that of a charged lepton and a neutrino at future 100 TeV collider experiments. It is revealed that this search method is suitable in particular for Higgsino, providing us the $5σ$ discovery reach of Higgsino in supersymmetric model with mass up to 850 GeV. We also discuss how accurately one can extract the mass, gauge charge, and spin of EWIMPs in our method.

hep-ph↗

arXiv2019

Loop corrections to dark matter direct detection in a pseudoscalar mediator dark matter model

If dark matter (DM) is a fermion and its interactions with the standard model particles are mediated by pseudoscalar particles, the tree-level amplitude for the DM-nucleon elastic scattering is suppressed by the momentum transfer in the non-relativistic limit. At the loop level, on the other hand, the spin-independent contribution to the cross section appears without such suppression. Thus, the loop corrections are essential to discuss the sensitivities of the direct detection experiments for the model prediction. The one-loop corrections were investigated in the previous works. However, the two-loop diagrams give the leading order contribution to the DM-gluon effective operator ($\barχ χG^{a}_{μν} G^{a μν} $) and have not been correctly evaluated yet. Moreover, some interaction terms which affect the scattering cross section were overlooked. In this paper, we show the cross section obtained by the improved analysis and discuss the region where the cross section becomes large.

hep-ph↗