arXiv subjects

Yuki Watanabe

Publications and source records attributed to Yuki Watanabe.

At least 19 recordsLinked to original sources

arXiv2026

Floquet Driving of Enzymatic Reactions: Counting Statistics and Long-Time Currents

Technologies for artificially controlling chemical reaction systems, such as optogenetics, are rapidly advancing, making it increasingly important to understand reaction dynamics under time-dependent control. When the modulation of reaction rates is periodic in time, the Floquet formalism provides a systematic framework. We develop a Floquet theory for classical stochastic processes that enables the calculation of the current and its counting statistics under such periodic modulation. In particular, we formulate the theory in terms of a counting field and derive general expressions for the first cumulant and the corresponding current. The current is expressed using the effective Floquet generator and the kicked state, and we further obtain general asymptotic expressions for the current in both the high- and low-frequency regimes. As a concrete example to test our analytical expressions, we then apply the results to discrete Floquet driving -- a non-perturbative, stepwise protocol. The setup is motivated by a biochemical system known as cyclic adenosine monophosphate (cAMP) production, which is an enzymatic reaction activated and inhibited by G-proteins. This is formulated as a discretely driven Michaelis--Menten-type reaction model, in which the catalytic activity is switched on and off abruptly in time, and we obtain analytical expressions and numerical results showing how periodic switching of reaction rates generates a long-time product current. In particular, in the high-frequency limit, we show that the effect of the periodic driving can be interpreted through an effective modification of the chemical reaction rates. These results provide a basis for Floquet analysis of periodically driven chemical reactions.

cond-mat.stat-mech↗

arXiv2026

Quantum electrometry in a silicon carbide power device

For high-bias operation devices such as silicon carbide (SiC) power devices, early detection of failure mechanisms is essential to ensure reliability. This requires a method to map high electric fields with high spatial resolution, which has not been realized until now. Here we report that the silicon vacancy (Vsi) in SiC has outstanding characteristics for detecting electric fields applied in various directions within a high-biased SiC device. Vsi exhibits an equivalent response to electric field components parallel (Epara) and perpendicular (Eperp) to the c-axis, a feature unique among quantum sensors, and the responsiveness to Epara and Eperp enables detection of arbitrary electric fields encountered in cutting-edge SiC power devices. We confirmed high electric field detection of ~2.3 MV/cm, which is ~90% of the breakdown electric field of a 4H-SiC with typical carrier concentration. Selectively formed Vsi enables high-resolution mapping of electric field distribution. Vsi-based quantum sensors bring data-driven research and development methodologies as well as device degradation diagnosis.

quant-ph↗

arXiv2026

Tree codes and sort-and-sweep algorithms for neighborhood computation: A cache-conscious comparison

Neighborhood algorithms may take a considerable percentage of computer time in discrete element methods (DEM). While the sort-and-sweep algorithm is ideal in some ways, as it only deal with particles whose relative positions change in one coordinate direction, the other directions must be processed too, for all particles. In contrast, tree-codes deal only with adjacent particles. We compare sort-and-sweep and tree-code neighborhood algorithms for two-dimensional DEM simulations of polygonal particles in a rotating drum with up to 12000 particles. We discuss the effects of system size and inlining on the performance with respect to the cache memory. For the tree code, the performance is slightly better, at the cost of significantly increased cyclomatic complexity. In particular, one benefit is improved possibilities for shared memory parallelization.

physics.comp-ph↗

arXiv2026

Light neutrinophilic WIMP in the $U(1)_{\rm B-L+xY}$ model

Sub-GeV dark matter is an appealing thermal target because it can still be produced via the standard freeze-out mechanism; at such low masses, achieving freeze-out naturally points to the presence of a light mediator, which shifts the most promising discovery avenues from the energy frontier to the intensity frontier. Realizing this picture is nonetheless challenging, since CMB observations tightly constrain energy injection from dark-matter annihilation at recombination and therefore strongly disfavor simple $s$-wave annihilation into visible Standard-Model final states. In this work, we propose a concrete neutrinophilic framework for sub-GeV thermal dark matter (''light WIMPs'') based on an additional gauge symmetry $\mathrm{U}(1)_{\mathrm{B}-\mathrm{L}+x\mathrm{Y}}$; for an appropriate choice of $x$, the new gauge boson couples predominantly to dark matter and neutrinos while its couplings to charged leptons are suppressed, so that sub-GeV dark matter annihilates almost exclusively into neutrinos, with hadronic modes kinematically closed. We map the parameter space in which the observed relic abundance is reproduced via standard thermal freeze-out in a conventional cosmological history, and show that sizable regions remain viable after imposing current cosmological, indirect-detection, and terrestrial constraints; in part of the allowed parameter space, the dark matter also exhibits sufficiently large self-interactions to potentially alleviate small-scale structure tensions.

hep-ph↗

arXiv2025

Dark-pion dark matter beyond leading order: unitarized chiral dynamics

Dark pions are promising dark matter candidates, yet most analyses rely on leading-order (LO) chiral perturbation theory (ChPT). Motivated by the fact that, even for QCD pi-pi scattering, LO ChPT near threshold underestimates the isoscalar s-wave amplitude by an O(1) factor relative to high-precision dispersive results, we quantify how unitarization modifies the standard LO ChPT picture using the chiral unitary method, a nonperturbative resummation that implements the correct analytic structure with minimal input, and assess its impact on the phenomenology of dark-pion dark matter, taking SIMP and WIMP scenarios as canonical examples. We fix the subtraction constant to its natural estimate, interpreted as an effective cutoff at the chiral scale, so that the unitarized amplitudes depend only on the dark-pion mass and decay constant. We show that, depending on the coupling, the unitarized amplitudes develop resonance poles absent at LO, leading to sizable departures in 2-to-2 self-scattering, relevant for SIMP scenarios, and in annihilation including initial-state interaction effects, relevant for WIMP scenarios. These modifications, in turn, affect the viable parameter space. Although the subtraction constant is, from a model-building perspective, merely a parameter, a substantial deviation from its natural value would point to additional elementary resonances with the same quantum numbers.

hep-ph↗

arXiv2025

Unitarization of the Sommerfeld enhancement through the renormalization group

When a pair of dark matter particles interacts via a long-range force mediated by a light particle, their nonrelativistic annihilation cross section can be significantly enhanced - a phenomenon known as the Sommerfeld enhancement. This enhancement exhibits resonant behavior if the long-range potential supports shallow bound states or narrow resonances, which can lead to violations of the partial-wave unitarity bound. We identify the origin of this pathological behavior as the emergence of secular terms in perturbative expansions associated with low-energy composite states of the long-range potential. To address this issue, we propose a renormalization group improvement of the perturbative series. The resulting improved amplitude provides a unitarity-consistent form of the Sommerfeld enhancement, with its poles acquiring an imaginary part that reflects the decay width of the annihilating bound states. We also briefly discuss the implications of our approach from the perspective of Wilsonian renormalization group, and comment on its potential application to higher-order annihilation processes such as bound-state formation.

hep-ph↗

arXiv2025

Detecting Sterile Neutrino Dark Matter at MeV Gamma-Ray Observatories

We explore the indirect detection of sterile neutrino dark matter within the gauged $U(1)_{B-L}$ extension of the Standard Model, in which three right-handed neutrinos account for neutrino masses, the baryon asymmetry, and dark matter. Focusing on the MeV mass range, we investigate two decay channels: the radiative decay $N \to \nu \gamma$, which produces a monochromatic photon, and the three-body decay $N \to e^- e^+ \nu$, which leads to a 511 keV photon signal from positronium decay. Taking the upcoming COSI mission as a case study, we show that both signals are experimentally accessible and complementary, with the 511 keV channel extending the sensitivity reach up to $O(100)$ MeV. We propose a novel analysis strategy in Compton data space to isolate the diffuse 511 keV emission. Furthermore, we incorporate, for the first time, the Sommerfeld enhancement in the decay width of $N \to e^- e^+ \nu$, enabling more accurate predictions of the signal near the kinematic threshold. The combined observation of both channels would provide a distinctive and testable signature of the sterile neutrino dark matter hypothesis.

hep-ph↗

arXiv2025

Scalar field stochastic dynamics in de Sitter spacetime from exact solutions of quantum deficient oscillators

The stochastic dynamics of a scalar field in de Sitter spacetime can be regarded as a non-perturbative diffusion process, to which exact distribution and correlation functions are constructed by utilising the correspondence between diffusion and Schr\"{o}dinger equations. The Krein--Adler transformation of the quantum harmonic oscillator deletes several pairs of the energy levels to define anharmonic oscillators that we dub quantum deficient oscillators, based on which this article constructs a new class of exact solutions in stochastic inflation. In addition to the simplest single-well model, an exactly solvable double-well model is also presented. The results are further extended to exactly solvable models with multiple wells, allowing analytical studies on various cosmological phenomenologies.

hep-th↗

arXiv2025

Light WIMPs and MeV Gamma-ray Detection with COSI

Light weakly interacting massive particles (WIMPs), whose masses are in the sub-GeV scale, have been attracting more attention due to the negative results searching for traditional WIMPs. The light WIMPs are expected to produce gamma rays from annihilation in the MeV energy region. Advancements in technology have opened up possibilities to precisely detect MeV gamma rays, leading to the upcoming space-based mission of the Compton Spectrometer and Imager (COSI). We comprehensively and quantitatively study the phenomenology of light WIMPs to determine if the COSI observations will probe their viable model parameter regions. We first construct models to describe light WIMPs based on the minimality and renormalizability of quantum field theory. Next, we impose various constraints on the models obtained from cosmological observations (CMB, BBN) and dark matter searches (accelerator, underground, astrophysical experiments, etc.). Finally, we identify viable parameter regions in each model and discuss whether or not COSI will be sensitive to the parameter regions. We find that a velocity-dependent annihilation cross-section is predicted in some regions, enabling COSI to detect the dark matter signal while avoiding severe constraints from cosmological observations.

hep-ph↗

arXiv2024

Tree Code Based Neighborhood Algorithms for Discrete Element Methods

We report our experiences for the development of a neighborhood algorithm implemented via tree-codes to optimize the performance of a discrete element method (DEM) for convex polytopes. Our implementation of the two-dimensional tree code needs $N\log N$, as does the sort and sweep approach. For our choice of boundary conditions (a rotating drum) and system sizes (up to several thousand particles), the performance of the tree-code is slightly better, but the algorithm is considerably more complicated than the sort and sweep approach.

physics.comp-ph↗

arXiv2024

Féeton dark matter above the $e^-e^+$ threshold

The new gauge boson introduced in the minimal extension of the standard model (SM) by gauging the U(1)$_{\rm B-L}$ symmetry plays the role of dark matter when the U(1)$_{\rm B-L}$ gauge coupling is highly suppressed. This dark matter, named the Féeton dark matter is known to be efficiently created in the early universe by inflationary fluctuations with minimal gravity coupling, hence the framework, the gauged U(1)$_{\rm B-L}$ extended SM + inflation, solves the four major problems of the SM; neutrino masses/mixings, dark matter, baryon asymmetry of the universe, and the initial condition of the universe (inflation). We comprehensively study the phenomenology of the dark matter when it is heavier than the $e^- e^+$ threshold, namely twice the electron mass, considering the threshold effect on the dark matter decay into $e^- e^+$. The viable parameter region is found only in the threshold region, while the branching fraction of the decay into $e^- e^+$ (i.e., the $e^- e^+$ signal) never vanishes even at the threshold due to the effect. As a result, the pure U(1)$_{\rm B-L}$ extension without the kinetic mixing between the U(1)$_{\rm B-L}$ and hyper-charge gauge bosons have already been excluded by the present observation of the 511\,keV photon from the galactic center. So, the Féeton dark matter requires a non-zero kinetic mixing to be a viable dark matter candidate and will be efficiently explored by future MeV-gamma ray telescopes thanks to the non-vanishing decay process into $e^- e^+$.

hep-ph↗

arXiv2024

Mediator Decay through mixing with Degenerate Spectrum

The decay of the mediator particle into standard model (SM) particles plays a significant role in exploring the dark sector scenario. We consider such a decay, taking the dark photon mediator as an example that mixes with the SM photon. We find that it requires a careful analysis of the decay rate in the presence of an SM vector boson (e.g., $Z$ boson, $\rho$ meson, and true muonium, etc.) nearly degenerate with the mediator particle in mass. The decay rate of the mediator particle calculated in the mass eigenstate basis {\bf does not} agree with the correct result, given by the imaginary parts of the poles for the vector boson propagators, when the mixing parameter is smaller than a specific value. In such a case, the decay rate calculated by treating the mixing as a perturbative parameter is in agreement with the correct result. We clarify specific values for the mixing parameter quantitatively using several concrete examples of the SM vector bosons degenerate with the dark photon. When the mass mixing between the vector boson and dark photon is smaller (larger) than the decay width of the vector boson, the latter (former) method to calculate the decay rate of the mediator particle gives the correct result.

hep-ph↗

arXiv2022

Decay of the Mediator Particle at Threshold

A light mediator particle is often predicted in the dark sector scenario, which weakly interacts with the standard model (SM) particles. The weakness of the interaction is usually described by a small coupling; however, the small coupling does not always guarantee the weakness of the interaction. When the mass of the mediator particle lies in a threshold region, the so-called threshold singularity may emerge, and then the perturbative calculation fails. This singularity causes several effects, e.g., the mixing between the mediator particle and bound states, the Sommerfeld effect on the final state of the mediator particle decay, etc. Taking the minimal model of the vector mediator particle decaying mainly into the SM particles as an example, we develop a method to describe the singularity quantitatively. We also calculate some physical quantities using this method, such as the lifetime of the mediator particle, and find that those could be significantly altered compared with the result of the perturbative calculation.

hep-ph↗

arXiv2020

Gravitational Wave from Axion-SU(2) Gauge Fields: Effective Field Theory for Kinetically Driven Inflation

Building on Weinberg's approach to effective field theory for inflation, we construct an effective Lagrangian for a pseudo scalar (axion) inflaton field with shift symmetry. In this Lagrangian we allow the axion field to couple to non-Abelian gauge fields via a Chern-Simons term. We then analyze a class of inflation models driven by kinetic terms. We find that the observational constraints on the amplitudes of curvature perturbations and non-Gaussianity yield a lower bound for the tensor-to-scalar ratio of $r\gtrsim 5\times 10^{-3}$ from the vacuum fluctuation. The sourced gravitational wave from SU(2) gauge fields further increases the tensor-to-scalar ratio and makes the total gravitational wave partially chiral and non-Gaussian, which can be probed by polarization of the cosmic microwave background and direct detection experiments. We discuss constraints on parameter space due to backreaction of spin-2 particles produced by the gauge field.

hep-th↗

arXiv2020

Effects of Gravitational Chern-Simons during Axion-SU(2) Inflation

In this paper, we examine the viability of inflation models with a spectator axion field coupled to both gravitational and SU(2) gauge fields via Chern-Simons couplings. Requiring phenomenological success of the axion-SU(2) sector constrains the coupling strength of the gravitational Chern-Simons term. We find that the impact of this term on the production and propagation of gravitational waves can be as large as fifty percent enhancement for the helicity that is not sourced by the gauge field, if the cut-off scale is as low as $Λ$ = 20H. The effect becomes smaller for a larger value of $Λ$, while the impact on the helicity sourced by the gauge field is negligible regardless of $Λ$.

gr-qc↗

arXiv2019

Active Generative Adversarial Network for Image Classification

Sufficient supervised information is crucial for any machine learning models to boost performance. However, labeling data is expensive and sometimes difficult to obtain. Active learning is an approach to acquire annotations for data from a human oracle by selecting informative samples with a high probability to enhance performance. In recent emerging studies, a generative adversarial network (GAN) has been integrated with active learning to generate good candidates to be presented to the oracle. In this paper, we propose a novel model that is able to obtain labels for data in a cheaper manner without the need to query an oracle. In the model, a novel reward for each sample is devised to measure the degree of uncertainty, which is obtained from a classifier trained with existing labeled data. This reward is used to guide a conditional GAN to generate informative samples with a higher probability for a certain label. With extensive evaluations, we have confirmed the effectiveness of the model, showing that the generated samples are capable of improving the classification performance in popular image classification tasks.

cs.LG↗

arXiv2018

Data Efficient Lithography Modeling with Transfer Learning and Active Data Selection

Lithography simulation is one of the key steps in physical verification, enabled by the substantial optical and resist models. A resist model bridges the aerial image simulation to printed patterns. While the effectiveness of learning-based solutions for resist modeling has been demonstrated, they are considerably data-demanding. Meanwhile, a set of manufactured data for a specific lithography configuration is only valid for the training of one single model, indicating low data efficiency. Due to the complexity of the manufacturing process, obtaining enough data for acceptable accuracy becomes very expensive in terms of both time and cost, especially during the evolution of technology generations when the design space is intensively explored. In this work, we propose a new resist modeling framework for contact layers, utilizing existing data from old technology nodes and active selection of data in a target technology node, to reduce the amount of data required from the target lithography configuration. Our framework based on transfer learning and active learning techniques is effective within a competitive range of accuracy, i.e., 3-10X reduction on the amount of training data with comparable accuracy to the state-of-the-art learning approach.

cs.LG↗

arXiv2018

Probing the BSM physics with CMB precision cosmology: an application to supersymmetry

The cosmic history before the BBN is highly determined by the physics that operates beyond the Standard Model (BSM) of particle physics and it is poorly constrained observationally. Ongoing and future precision measurements of the CMB observables can provide us with significant information about the pre-BBN era and hence possibly test the cosmological predictions of different BSM scenarios. Supersymmetry is a particularly motivated BSM theory and it is often the case that different superymmetry breaking schemes require different cosmic histories with specific reheating temperatures or low entropy production in order to be cosmologically viable. In this paper we quantify the effects of the possible alternative cosmic histories on the $n_s$ and $r$ CMB observables assuming a generic non-thermal stage after cosmic inflation. We analyze TeV and especially multi-TeV supersymmetry breaking schemes assuming the neutralino and gravitino dark matter scenarios. We complement our analysis considering the Starobinsky $R^2$ inflation model to exemplify the improved CMB predictions that a unified description of the early universe cosmic evolution yields. Our analysis underlines the importance of the CMB precision measurements that can be viewed, to some extend, as complementary to the laboratory experimental searches for supersymmetry or other BSM theories.

hep-ph↗