arXiv subjects

Akihiro Nakamura

Publications and source records attributed to Akihiro Nakamura.

At least 19 recordsLinked to original sources

arXiv2025

Accuracy-Preserving Calibration via Statistical Modeling on Probability Simplex

Classification models based on deep neural networks (DNNs) must be calibrated to measure the reliability of predictions. Some recent calibration methods have employed a probabilistic model on the probability simplex. However, these calibration methods cannot preserve the accuracy of pre-trained models, even those with a high classification accuracy. We propose an accuracy-preserving calibration method using the Concrete distribution as the probabilistic model on the probability simplex. We theoretically prove that a DNN model trained on cross-entropy loss has optimality as the parameter of the Concrete distribution. We also propose an efficient method that synthetically generates samples for training probabilistic models on the probability simplex. We demonstrate that the proposed method can outperform previous methods in accuracy-preserving calibration tasks using benchmarks. The code is available at https://github.com/ToyotaCRDL/SimplexTS.

cs.LG↗

arXiv2023

StyleDiff: Attribute Comparison Between Unlabeled Datasets in Latent Disentangled Space

One major challenge in machine learning applications is coping with mismatches between the datasets used in the development and those obtained in real-world applications. These mismatches may lead to inaccurate predictions and errors, resulting in poor product quality and unreliable systems. In this study, we propose StyleDiff to inform developers of the differences between the two datasets for the steady development of machine learning systems. Using disentangled image spaces obtained from recently proposed generative models, StyleDiff compares the two datasets by focusing on attributes in the images and provides an easy-to-understand analysis of the differences between the datasets. The proposed StyleDiff performs in $O (d N\log N)$, where $N$ is the size of the datasets and $d$ is the number of attributes, enabling the application to large datasets. We demonstrate that StyleDiff accurately detects differences between datasets and presents them in an understandable format using, for example, driving scenes datasets.

stat.ML↗

arXiv2022

A Markov chain approximation of switched Fokker-Planck equations for a model of on-off intermittency in the postural control during quiet standing

The intermittent on-off switching of feedback control is considered as a major mechanism of postural stabilization during human quiet standing, which can be modeled by switched-type hybrid stochastic delay differential equations with unstable subsystems. Dynamics of the model can also be described by the corresponding switched-type Fokker-Planck (FP) equations. Here, we develop a comprehensive numerical recipe to simulate switched-type FP equations in the case that the probability current is conserved at the switching boundary, as is the case for noise-free models exhibiting C^0-continuity for solutions at the boundary, but in a way extendable to cases with discontinuous jump. Specifically, the FP equations are approximated by a finite state Markov chain model using the finite element method. Then, dynamics of the Markov chain model, including time evolution of probability density function (PDF), stationary PDF, and power spectrum of postural sway are analyzed. We further investigate how the stationary PDF alters as values of important parameters of the model change. Dynamics of the Markov chain model are compared with Monte Carlo-based dynamics of the model, by which the developed numerical recipe is validated. The obtained Markov chain model forms a basis of our future investigations of the intermittent postural control as a Markov decision process.

eess.SY↗

arXiv2019

Revisiting Fine-tuning for Few-shot Learning

Few-shot learning is the process of learning novel classes using only a few examples and it remains a challenging task in machine learning. Many sophisticated few-shot learning algorithms have been proposed based on the notion that networks can easily overfit to novel examples if they are simply fine-tuned using only a few examples. In this study, we show that in the commonly used low-resolution mini-ImageNet dataset, the fine-tuning method achieves higher accuracy than common few-shot learning algorithms in the 1-shot task and nearly the same accuracy as that of the state-of-the-art algorithm in the 5-shot task. We then evaluate our method with more practical tasks, namely the high-resolution single-domain and cross-domain tasks. With both tasks, we show that our method achieves higher accuracy than common few-shot learning algorithms. We further analyze the experimental results and show that: 1) the retraining process can be stabilized by employing a low learning rate, 2) using adaptive gradient optimizers during fine-tuning can increase test accuracy, and 3) test accuracy can be improved by updating the entire network when a large domain-shift exists between base and novel classes.

cs.LG↗

arXiv2019

Noise-Level Estimation from Single Color Image Using Correlations Between Textures in RGB Channels

We propose a simple method for estimating noise level from a single color image. In most image-denoising algorithms, an accurate noise-level estimate results in good denoising performance; however, it is difficult to estimate noise level from a single image because it is an ill-posed problem. We tackle this problem by using prior knowledge that textures are highly correlated between RGB channels and noise is uncorrelated to other signals. We also extended our method for RAW images because they are available in almost all digital cameras and often used in practical situations. Experiments show the high noise-estimation performance of our method in synthetic noisy images. We also applied our method to natural images including RAW images and achieved better noise-estimation performance than conventional methods.

cs.CV↗

arXiv2014

Glueball instability and thermalization driven by dark radiation

We study glueballs in the holographic gauge theories living in a curved space-time. The dual bulk is obtained as a solution of the type IIB superstring theory with two parameters, which correspond to four dimensional (4D) cosmological constant $λ$ and the dark radiation $C$ respectively. The theory is in the confining phase for $λ<0$ and small $C$, then we observe stable glueball states in this theory. However, the stability of the glueball states is lost when the density of the dark radiation ($C$) increases and exceeds a critical point. Above this point, the dark radiation works as the heat bath of the Yang-Mills theory since the event horizon appears. Thus the system is thermalized, and the theory is in a finite temperature deconfinement phase, namely in the QGP phase. We observe this transition process through the glueball spectra which varies dramatically with $C$. We also examined the entanglement entropy of the system to find a clue of this phase transition and the role of the dark radiation $C$ in the entanglement entropy.

hep-th↗

arXiv2014

Ad$S_5$ with two boundaries and holography of $\cal{N}=$4 SYM theory

According to the AdS/CFT correspondence, the ${\cal N}=4$ supersymmetric Yang-Mills (SYM) theory is studied through its gravity dual whose configuration has two boundaries at the opposite sides of the fifth coordinate. At these boundaries, in general, the four dimensional (4D) metrics are different, then we expect different properties for the theory living in two boundaries. It is studied how these two different properties of the theory are obtained from a common 5D bulk manifold in terms of the holographic method. We could show in our case that the two theories on the different boundaries are described by the Ad$S_5$, which is separated into two regions by a domain wall. This domain wall is given by a special point of the fifth coordinate. Some issues of the entanglement entropy related to this bulk configuration are also discussed.

hep-th↗

arXiv2013

Holographic Friedmann Equation and $\cal{N}=$4 SYM theory

According to the AdS/CFT correspondence, the ${\cal N}=4$ supersymmetric Yang-Mills (SYM) theory has been studied by solving the dual supergravity. In solving the bulk Einstein equation, we find that it could be related to the 4D Friedmann equation, which is solved by using the cosmological constant and the energy density of the matters on the boundary, and they are dynamically decoupled from the SYM theory. We call this combination of the bulk Einstein equations and the 4D Friedmann equation as holographic Friedmann equations (HFE). Solving the HFE, it is shown how the 4D decoupled matters and the cosmological constant control the dynamical properties of the SYM theory, quark confinement, chiral symmetry breaking, and baryon stability. From their effect on the SYM, the matters are separated to two groups. Our results would give important information in studying the cosmological development of our universe.

hep-th↗

arXiv2010

Stability of D brane Anti D brane Systems in Confining Gauge Theories

We study the stability of a special form of D brane embedding which is regarded as a bound state of D$_n$ and anti-D$_n$-brane embedded in a 10D supergravity background which is dual to a confining gauge theory. For D5 branes with $U(1)$ flux, their bound state configuration can be regarded as the baryonium vertex. For D branes of $n=6$ and 8 without the $U(1)$ flux, their bound states have been used to introduce flavor quarks in the dual supersymmetric Yang-Mills theory. In any case, it would be important to assure that they are free from tachyon instability. For all these cases, we could show their stability with respect to this point.

hep-th↗

arXiv2010

Holographic Penta and Hepta Quark State in Confining Gauge Theories

We study a new embedding solutions of D5 brane in an asymptotic AdS${}_5\times S^5$ space-time, which is dual to a confining $SU(N_c)$ gauge theory. The D5 brane is wrapped on $S^5$ as in the case of the vertex of holographic baryon. However, the solution given here is different from the usual baryon vertex in the point that it couples to $k$-anti-quarks and $N_c+k$ quarks on the opposite two points of $S^5$, the north and south poles, respectively. The total quark number of this state is preserved as $N_c$ when minus one is assigned to anti-quark, then it forms a color singlet like the baryon. However, this includes anti-quarks and quarks, whose number is larger than that of the baryon. When we set as $N_c=3$, we find the so called penta and hepta-quark states. We study the dynamical properties of these states by solving the vertex and string configurations for such states. The mass spectra of these states and the tension of the stretched vertex are estimated, and they are compared with that of the baryon.

hep-th↗

arXiv2009

Baryonium in Confining Gauge Theories

We show a new class of embedding solutions of D5 brane, which wraps on $S^5$ in the AdS${}_5\times S^5$ space-time and contains fundamental strings as U(1) flux to form a baryon vertex. The new solution given here is different from the baryon vertex since it consists of two same side (north or south) poles of $S^5$ as cusps, which are put on different points in our three dimensional space. This implies that the same magnitude of electric displacement exists at each cusp, but their orientations are opposite due to the flux number conservation. This configuration is therefore regarded as a D5-$\bar{D5}$ bound state, and we propose this as the vertex of a baryonium state, which is made of a baryon and an anti-baryon. By attaching quarks and anti-quarks to the two cusps of this vertex, it is possible to construct a realistic baryonium.

hep-th↗

arXiv2008

Multi-quark baryons and color screening at finite temperature

We study baryons in SU(N) gauge theories at finite temperature according to the gauge/string correspondence based on IIB string theory. The baryon is constructed out of D5 brane and $N$ fundamental strings to form a color singlet $N$-quark bound state. At finite temperature and in the deconfining phase, we could find $k(<N)$-quark ``baryons''. Thermal properties of such $k$-quark baryons and also of the $N$-quark baryon are examined. We study the temperature dependence of color screening distance and Debye length of the baryon of $k$-quark and $N$-quark. We also estimate the melting temperature, where the baryons decay into quarks and gluons completely.

hep-th↗

arXiv2007

D3/D7 holographic Gauge theory and Chemical potential

N=2 supersymmetric Yang-Mills theory with flavor hypermultiplets at finite temperature and in the dS${}_4$ are studied for finite quark number density ($n_b$) by a dual supergravity background with non-trivial dilaton and axion. The quarks and its number density $n_b$ are introduced by embedding a probe D7 brane. We find a critical value of the chemical potential at the limit of $n_b=0$, and it coincides with the effective quark mass given in each theory for $n_b=0$. At this point, a transition of the D7 embedding configurations occurs between their two typical ones. The phase diagrams of this transition are shown in the plane of chemical potential versus temperature and cosmological constant for YM theory at finite temperature and in dS${}_4$ respectively. In this phase transition, the order parameter is considered as $n_b$. % and the critical value of the chemical potential This result seems to be reasonable since both theories are in the quark deconfinement phase.

hep-th↗

arXiv2006

Flavor quarks in AdS4 and gauge/gravity correspondence

The non-perturbative properties of the gauge theories in the AdS${}_4$ are studied in the dual supergravity by including light flavor quarks, which are introduced by a D7 brane embedding. Contrary to the cases of Minkowski and dS${}_4$, the dilaton does not play any important dynamical role in the AdS${}_4$ case, and the characteristic properties like the quark confinement and the chiral symmetry breaking are realized mainly due to the geometry AdS${}_4$. The possible hadron spectra %in the AdS${}_4$ are also examined, and we find that the meson spectra are well described by the formula given by the field theory in AdS${}_4$, but the characteristic mass scale is modified by the gauge interactions for exited states.

hep-th↗

arXiv2006

Gauge theory in de Sitter space-time from a holographic model

Yang-Mills theory with flavor quarks in the dS${}_4$ is studied through the dual supergravity in the AdS${}_5\times S^5$ background with non-trivial dilaton and axion. The flavor quarks are introduced by embedding a probe D7 brane. We find that the dynamical properties of YM theory in the dS${}_4$ are similar to the case of the finite temperature theory given by the 5d AdS-Schwarzschild background. In the case of dS${}_4$, however, contrary to the finite temperature case, the gauge field condensate plays an important role on the dynamical properties of quarks. We also give the quark-antiquark potential and meson spectra to find possible quark-bound states. And we arrive at the conclusion that, while the quarks are not confined in the dS${}_4$, we could find stable meson states at very small cosmological constant as expected in the present universe. But there would be no hadrons at early universe as in the inflation era.

hep-th↗

arXiv2006

Holographic Model at Finite Temperature with $R$-chrage density

We consider a holographic model of QCD at finite temperature with nonzero chemical potentials conjugate to $R$-charge densities. A critical surface of the confinement-deconfinement phase transition is shown for five-dimensional charged black hole solution given by Behrnd, Cvetič and Sabra. On a special section of the parameter space, we find an critical curve being similar to the one expected in QCD. We calculate meson spectra and decay constants in the confinement phase of this section to see their temperature and chemical potential dependences. We could assure generalized GellMann-Oakes-Renner relation and the reduction of pion velocity near the critical point.

hep-ph↗

arXiv2005

Meson mass and confinement force driven by dilaton

Meson spectra given as fluctuations of a D7 brane are studied under the background driven by the dilaton. This leads to a dual gauge theory with quark confinement due to the gauge condensate. We find that the effect of the gauge condensate on the meson spectrum is essential in order to make a realistic hadron spectrum in the non-supersymmetric case. In the supersymmetric case, however, only the spectra of the scalars are affected, but they are changed in an opposite way compared to the non-supersymmetric case.

hep-th↗

arXiv2003

Newton's law in de Sitter brane

Newton potential has been evaluated for the case of dS brane embedded in Minkowski, dS$_5$ and AdS$_5$ bulks. We point out that only the AdS$_5$ bulk might be consistent with the Newton's law from the brane-world viewpoint when we respect a small cosmological constant observed at present universe.

hep-th↗