arXiv subjects

Takafumi Aoki

Publications and source records attributed to Takafumi Aoki.

22 records · Page 2Linked to original sources

arXiv2024

Small Instanton Effects on Composite Axion Mass

This paper investigates the impact of small instanton effects on the axion mass in composite axion models. In particular, we focus on the Composite Accidental Axion (CAA) models, which are designed to address the axion quality problem, and where the Peccei-Quinn (PQ) symmetry emerges accidentally. In the CAA models, the QCD gauge symmetry is embedded in a larger gauge group at high energy. These models contain small instantons not included in low-energy QCD, which could enhance the axion mass significantly. However, in the CAA models, our analysis reveals that these effects on the axion mass are non-vanishing but are negligible compared to the QCD effects. The suppression of the small instanton effects originates from the global chiral U(1) symmetries which are not broken spontaneously and play a crucial role in eliminating $θ$-terms in the hidden sectors through anomalies. We find these U(1) symmetries restrict the impact of small instantons in hidden sectors on the axion mass. Our study provides crucial insights into the dynamics within the CAA models and suggests broader implications for understanding small instanton effects in other composite axion models.

hep-ph↗

arXiv2023

Lattice study on a tetra-quark state $T_{bb}$ in the HAL QCD method

We study a doubly-bottomed tetra-quark state $(bb\bar{u}\bar{d})$ with quantum number $I(J^P)=0(1^+)$, denoted by $T_{bb}$, in lattice QCD with the Non-Relativistic QCD (NRQCD) quark action for $b$ quarks. Employing $(2+1)$-flavor gauge configurations at $a \approx 0.09$ {fm} on $32^3\times 64$ lattices, we have extracted the coupled channel potential between $\bar{B}\bar{B}^*$ and $\bar{B}^* \bar{B}^*$ in the HAL QCD method, which predicts an existence of a bound $T_{bb}$ below the $\bar{B}\bar{B}^*$ threshold. By extrapolating results at $m_π\approx 410,\, 570,\, 700$ {MeV} to the physical pion mass $m_π\approx140$ {MeV}, we obtain a biding energy with its statistical error as $E_{\rm binding}^{\rm (single)} = 155(17)$ MeV and $E_{\rm binding}^{\rm (coupled)} = 83(10)$ MeV, where ``coupled" means that effects due to virtual $\bar{B}^* \bar{B}^*$ states are included through the coupled channel potential, while only a potential for a single $\bar{B}\bar{B}^*$ channel is used in the analysis for ``single". A comparison shows that the effect from virtual $\bar{B}^* \bar{B}^*$ states is quite sizable to the binding energy of $T_{bb}$. We estimate systematic errors to be $\pm 20$ MeV at most, which are mainly caused by the NRQCD approximation for $b$ quarks.

hep-lat↗

arXiv2022

Lattice study on a tetraquark state $T_{bb}$ in the HAL QCD method

We investigate a doubly-bottomed tetraquark state $T_{bb}$ $(bb \bar{u}\bar{d})$ with quantum number $I(J^P)=0(1^+)$ in $(2+1)$-flavor lattice QCD. Using the Non-Relativistic QCD (NRQCD) quark action for $b$ quarks, we have extracted the coupled channel potential between $\bar{B}\bar{B}^*$ and $\bar{B}^* \bar{B}^*$ in the HAL QCD method at $a \approx 0.09$ {fm} on $32^3\times 64$ lattices. The potential predicts an existence of a bound $T_{bb}$ below the $\bar{B}\bar{B}^*$ threshold. At the physical pion mass $m_π\approx140$ {MeV} extrapolated from $m_π\approx 410,\, 570,\, 700$ {MeV}, a binding energy with its statistical error is given by $E_{\rm binding}^{\rm (coupled)} = 83(10)$ MeV from a coupled channel analysis where effects due to virtual $\bar{B}^* \bar{B}^*$ states are included through the coupled channel potential, while we obtain $E_{\rm binding}^{\rm (single)} = 155(17)$ MeV only from a potential for a single $\bar{B}\bar{B}^*$ channel. This difference indicates that the effect from virtual $\bar{B}^* \bar{B}^*$ states is sizable to the binding energy of $T_{bb}$. Adding $\pm 20$ MeV as empirical systematic error caused by the NRQCD approximation for $b$ quarks, our estimate of the $T_{bb}$ binding energy becomes $83(10)(20)$ MeV.

hep-lat↗

arXiv2020

Fingerprint Feature Extraction by Combining Texture, Minutiae, and Frequency Spectrum Using Multi-Task CNN

Although most fingerprint matching methods utilize minutia points and/or texture of fingerprint images as fingerprint features, the frequency spectrum is also a useful feature since a fingerprint is composed of ridge patterns with its inherent frequency band. We propose a novel CNN-based method for extracting fingerprint features from texture, minutiae, and frequency spectrum. In order to extract effective texture features from local regions around the minutiae, the minutia attention module is introduced to the proposed method. We also propose new data augmentation methods, which takes into account the characteristics of fingerprint images to increase the number of images during training since we use only a public dataset in training, which includes a few fingerprint classes. Through a set of experiments using FVC2004 DB1 and DB2, we demonstrated that the proposed method exhibits the efficient performance on fingerprint verification compared with a commercial fingerprint matching software and the conventional method.

cs.CV↗