arXiv subjects

Syo Kamata

Publications and source records attributed to Syo Kamata.

At least 19 recordsLinked to original sources

arXiv2026

Universal Relations for Neutron Stars from Asymptotic Analysis

Dimensionless observables of neutron stars, such as the moment of inertia, the tidal deformability, the spin-induced quadrupole moment, and the compactness, satisfy the I--Love--Q and Love--$C$ universal relations to percent-level accuracy over a wide range of equations of state. We investigate analytically the origin of this insensitivity in the stellar structure equations. We derive asymptotic expansions of these relations directly from the differential equations and boundary conditions for slowly rotating, tidally deformed stars described by a general piecewise-polytropic equation of state. Although the differential equations allow several forms of the asymptotic expansion, we find that only one class is consistent with the observed universality, and we use this class to analyze the universal relations. Because the observables are determined at the stellar surface, information about the deep-interior equation of state can enter them only through the parameters that survive in the asymptotic expansion at the surface. We find that the universal relations depend only on three parameters: two integration constants and one polytrope index of the outermost segment. By determining how these parameters deform the relations, we show that, throughout the region of parameter space occupied by realistic equations of state, the resulting deviations remain at the percent level, consistent with the observed accuracy of the universal relations. Within the same formalism, we classify violations of universality according to the additional degrees of freedom or input data responsible for them. Since the construction relies only on the underlying differential equations and boundary conditions, the same procedure can be applied to other systems once the corresponding equations and boundary conditions are specified.

gr-qc↗

arXiv2026

Algebraic Tomography of Non-Hermitian Floquet Systems from Observable Traces

We formulate a framework of Floquet algebraic tomography for finite-dimensional non-Hermitian monodromy matrices from observable trace sequences $\zeta_n^{(O)}={\rm Tr}(OM^n)$. Since these sequences are constrained by the characteristic polynomial of $M$, the inverse problem is a finite-dimensional algebraic reconstruction problem rather than a generic exponential fit. We organize the reconstruction through the observable resolvent, spectral determinant, and Dirichlet spectral data, separating the common spectral skeleton from observable-dependent dressing. Cayley--Hamilton and Hankel methods recover the similarity-invariant spectral data, while multi-observable and Liouville-space extensions connect the construction to realization theory and tomography reconstruction. We further clarify the limits of identifiability from restricted observable algebras: the data determine a visible representative, micromotion can enlarge the sampled visible operator space, and exact symmetries impose residual invisible sectors. Two examples, a driven transmon qutrit and a finite non-Hermitian Floquet SSH chain, demonstrate leakage-induced visibility expansion, observable-dependent phase response, EP-accessible branch geometry, and disorder/probe-dependent observable-dimension readouts.

quant-ph↗

arXiv2026

Exact WKB analysis of inverted triple-well: resonance, PT-symmetry breaking, and resurgence

We study non-Hermitian quantum mechanics of an inverted triple-well potential within the exact WKB framework. For a single classical potential, different Siegert boundary conditions define three distinct quantum problems: the PT-symmetric, resonance, and anti-resonance systems. For each case, we derive the exact quantization condition and construct the associated trans-series solution. By identifying the resurgent structures and cancellations in these non-Hermitian setups, we obtain the median-summed series, clarifying when the spectra are real or complex in accordance with the physical properties of each system. Establishing explicit links to the semi-classical path integral formalism, we elucidate the roles of bounce and bion configurations in these non-Hermitian systems. This analysis predicts PT-symmetry breaking, which we also verify numerically. Using the median quantization conditions, we prove the existence of this symmetry breaking and establish an exact equation for the exceptional point, which emerges as a remarkably simple algebraic relation between the bounce and bion actions. We further show that the median-summed non-perturbative correction to the spectrum vanishes at the exceptional point, while the resurgent structure survives through a universal minimal trans-series. For the resonance and anti-resonance systems, we find that the exact median-summed spectra are related by complex conjugation, representing time reversal in this setting, are necessarily complex, and do not exhibit an exceptional point. Although their spectra differ significantly from the PT-symmetric case, they share the same minimal trans-series. By maintaining explicit links with the path integral saddles and the formal theory of resurgence, our analysis provides a unified and general perspective on the quantization of non-Hermitian theories.

hep-th↗

arXiv2025

Topological Uncertainty for Anomaly Detection in the Neural-network EoS Inference with Neutron Star Data

We study the performance of the Topological Uncertainty (TU) constructed with a trained feedforward neural network (FNN) for Anomaly Detection. Generally, meaningful information can be stored in the hidden layers of the trained FNN, and the TU implementation is one tractable recipe to extract buried information by means of the Topological Data Analysis. We explicate the concept of the TU and the numerical procedures. Then, for a concrete demonstration of the performance test, we employ the Neutron Star data used for inference of the equation of state (EoS). For the training dataset consisting of the input (Neutron Star data) and the output (EoS parameters), we can compare the inferred EoSs and the exact answers to classify the data with the label $k$. The subdataset with $k=0$ leads to the normal inference for which the inferred EoS approximates the answer well, while the subdataset with $k=1$ ends up with the unsuccessful inference. Once the TU is prepared based on the $k$-labled subdatasets, we introduce the cross-TU to quantify the uncertainty of characterizing the $k$-labeled data with the label $j$. The anomaly or unsuccessful inference is correctly detected if the cross-TU for $j=k=1$ is smaller than that for $j=0$ and $k=1$. In our numerical experiment, for various input data, we calculate the cross-TU and estimate the performance of Anomaly Detection. We find that performance depends on FNN hyperparameters, and the success rate of Anomaly Detection exceeds $90\%$ in the best case. We finally discuss further potential of the TU application to retrieve the information hidden in the trained FNN.

nucl-th↗

arXiv2025

Exact Sum Rules and Zeta Generating Formulas from the ODE/IM correspondence

We develop a spectral-zeta framework for quantum mechanics with the ${\cal PT}$-symmetric potential $V_{{\cal PT}}(x)=x^{2K}(ix)^{\varepsilon}$ $(K,\varepsilon \in {\mathbb N})$ and the Hermitian potential $V_{{\cal H}}(x)=x^{2M}$ $(M \in {\mathbb N}+1)$, based on the fusion relations of the $A_{2M-1}$ T-system. Using the ODE/IM correspondence, we construct exact sum rules (ESRs) and zeta generating formulas (ZGFs) for the spectral zeta functions (SZFs) $\zeta_n(s)$. In contrast to recursive T-Q relations, the ZGFs provide fixed-source, closed-form mappings between different fusion sectors. For Hermitian $M=2$, our ESRs reproduce exact WKB results, extending them systematically to ${\cal PT}$ sectors and (half-)integer $M$. Our analysis reveals a phenomenon of \textit{algebraic information loss}, distinct from analytic ambiguity. The structure is governed by a selection rule ${\cal S}_n$, derived from the Chebyshev structure of fusion relations and $\mathbb{Z}_{2M+2}$ Symanzik symmetry. For odd integer $M$, we identify a structural non-invertibility: mapping from \textit{odd} to \textit{even} fusion sectors causes exact coefficient cancellation due to phase interference, rendering the map non-invertible. This implies even-sector data carry strictly less information than odd-sector data, yielding a \textit{no-go} statement for inverse spectral reconstruction. Conversely, for even and half-integer $M$, all relevant sectors form an information-equivalent, mutually invertible family. Finally, we provide a spectral-zeta formulation of the massless Ai-Bender-Sarkar (ABS) conjecture. By connecting ${\cal PT}$ and Hermitian spectra via ZGFs, we establish a purely spectral-theoretic route to the conjectured relation, avoiding explicit analytic continuation.

hep-th↗

arXiv2025

Exact-WKB Analysis of Two-level Floquet Systems

We explore the application of the exact Wentzel-Kramers-Brillouin (WKB) analysis to two-level Floquet systems and establish a systematic procedure to calculate the quasi-energy and Floquet effective Hamiltonian. We show that, in the exact-WKB analysis, the quasi-energy and Floquet effective Hamiltonian can be expressed in terms of cycle integrals (Voros symbol), which characterize monodromy matrices for Schr\"odinger-type differential equations governing two-level Floquet systems. We analytically evaluate the cycle integrals using the low-frequency expansion and derive both perturbative and non-perturbative corrections to the quasi-energy and Floquet effective Hamiltonian. To verify the accuracy of our results, we compare them with numerical calculations and analyze resonant oscillations, which reveal non-perturbative features that cannot be captured by the perturbative expansion.

hep-ph↗

arXiv2024

Stochastic quantization and diffusion models

This is a pedagogical review of the possible connection between the stochastic quantization in physics and the diffusion models in machine learning. For machine-learning applications, the denoising diffusion model has been established as a successful technique, which is formulated in terms of the stochastic differential equation (SDE). In this review, we focus on an SDE approach used in the score-based generative modeling. Interestingly, the evolution of the probability distribution is equivalently described by a particular class of SDEs, and in a particular limit, the stochastic noises can be eliminated. Then, we turn to a similar mathematical formulation in quantum physics, that is, the stochastic quantization. We make a brief overview on the stochastic quantization using a simple toy model of the one-dimensional integration. The analogy between the diffusion model and the stochastic quantization is clearly seen in this concrete example. Finally, we discuss how the sign problem arises in the toy model with complex parameters. The origin of the difficulty is understood based on the Lefschetz thimble analysis. We point out that the SDE is not invariant under the variable change which induces a kernel and a special choice of the kernel guided by the Lefschetz thimble analysis can reduce the sign problem.

hep-lat↗

arXiv2024

Exact quantization conditions and full transseries structures for ${\cal PT}$ symmetric anharmonic oscillators

We study exact Wentzel-Kramers-Brillouin analysis (EWKB) for a ${\cal PT}$ symmetric quantum mechanics (QM) defined by the potential that $V_{\cal PT}(x) = \omega^2 x^2 + g x^{2 K} (i x)^{\varepsilon}$ with $\omega \in {\mathbb R}_{\ge 0}$, $g \in {\mathbb R}_{>0}$ and $K, \varepsilon \in {\mathbb N}$ to clarify its perturbative/non-perturbative structure. In our analysis, we mainly consider the massless cases, i.e., $\omega = 0$, and derive the exact quantization conditions (QCs) for arbitrary $(K,\varepsilon)$ including all perturbative/non-perturbative corrections. From the exact QCs, we clarify full transseries structure of the energy spectra with respect to the inverse energy level expansion, and then formulate the Gutzwiller trace formula, the spectral summation form, and the Euclidean path-integral. For the massive cases, i.e., $\omega > 0$, we show the fact that, by requiring existence of solution of the exact QCs, the path of analytic continuation in EWKB is uniquely determined for a given $N = 2K + \varepsilon$, and in consequence the exact QCs, the energy spectra, and the three formulas are all perturbative. Similarities to Hermitian QMs and resurgence are also discussed as additional remarks.

hep-th↗

arXiv2024

Uncertainty quantification in the machine-learning inference from neutron star probability distribution to the equation of state

We discuss the machine-learning inference and uncertainty quantification for the equation of state (EoS) of the neutron star (NS) matter directly using the NS probability distribution from the observations. We previously proposed a prescription for uncertainty quantification based on ensemble learning by evaluating output variance from independently trained models. We adopt a different principle for uncertainty quantification to confirm the reliability of our previous results. To this end, we carry out the MC sampling of data to infer an EoS and take the convolution with the probability distribution of the observational data. In this newly proposed method, we can deal with arbitrary probability distribution not relying on the Gaussian approximation. We incorporate observational data from the recent multimessenger sources including precise mass measurements and radius measurements. We also quantify the importance of data augmentation and the effects of prior dependence.

nucl-th↗

arXiv2023

Exact WKB analysis for ${\cal PT}$ symmetric quantum mechanics: Study of the Ai-Bender-Sarkar conjecture

We consider exact WKB analysis to a ${\cal PT}$ symmetric quantum mechanics defined by the potential, $V(x) = \omega^2 x^2 + g x^2(i x)^{\varepsilon=2}$ with $\omega \in {\mathbb R}_{\ge 0}$, $g \in {\mathbb R} _{> 0}$. We in particular aim to verify a conjecture proposed by Ai-Bender-Sarkar (ABS), that pertains to a relation between $D$-dimensional ${\cal PT}$-symmetric theories and analytic continuation (AC) of Hermitian theories concerning the energy spectrum or Euclidean partition function. For the purpose, we construct energy quantization conditions by exact WKB analysis and write down their transseries solution by solving the conditions. By performing alien calculus to the energy solutions, we verify validity of the ABS conjecture and seek a possibility of its alternative form by Borel resummation theory if it is violated. Our results claim that the validity of the ABS conjecture drastically changes depending on whether $\omega > 0$ or $\omega = 0$: If ${\omega}>0$, then the ABS conjecture is violated when exceeding the semi-classical level of the first non-perturbative order, but its alternative form is constructable by Borel resummation theory. The ${\cal PT}$ and the AC energies are related to each other by a one-parameter Stokes automorphism, and a median resummed form, which corresponds to a formal exact solution, of the AC energy (resp. ${\cal PT}$ energy) is directly obtained by acting Borel resummation to a transseries solution of the ${\cal PT}$ energy (resp. AC energy). If $\omega = 0$, then, with respect to the inverse energy level-expansion, not only perturbative/non-perturbative structures of the ${\cal PT}$ and the AC energies but also their perturbative parts do not match with each other. These energies are independent solutions, and no alternative form of the ABS conjecture can be reformulated by Borel resummation theory.

hep-th↗

arXiv2022

Resurgence for the non-conformal Bjorken flow with Fermi-Dirac and Bose-Einstein statistics

We consider resurgence for the nonconformal Bjorken flow with Fermi-Dirac and Bose-Einstein statistics on the extended relaxation-time approximation. We firstly consider full formal transseries expanded around the equilibrium and then construct the resurgent relation by looking to the structure of Borel transformed ODEs. We form a conjecture of the resurgent relation based on the considerations that Stokes constants constituting of the resurgent relation originate only from singularities of dissipative variables on the Borel plane and that the other variables such as temperature and chemical potential become Borel nonsummable through nonlinear terms with the dissipative variables. We numerically check the conjecture for fundamental variables by explicitly evaluating values of the dominant Stokes constant depending on initial conditions and a particle mass. We also make comments on some issues related to transseries structure and resurgence such as the case of broken $U(1)$ symmetry, the massless case, generalized relaxation-time, and attractor solution.

hep-th↗

arXiv2022

Novel features of attractors and transseries in non-conformal Bjorken flows

In this work we investigate the impact of conformal symmetry breaking on hydrodynamization of a far-from-equilibrium fluid. We find a new kind of transseries solutions for the non-conformal hydrodynamic equations of a longitudinal boost invariant expanding plasma. The new transseries solutions unveil a rich physical structure which arises due to the interplay of different physical scales. In the perfect fluid case the non-conformal speed of sound slows down the cooling of the temperature due to the emergence of logarithmic corrections that depends on the mass of the particle. These terms propagate into the perturbative and non-perturbative sectors of the transseries once viscous corrections are included. The logarithmic mass contributions increase the asymptotic value of the Knudsen number while decreasing the damping rate of the transient non-hydrodynamic modes and thus, yielding to an extremely slow hydrodynamization process where flow lines merge to their forward attractor at extremely late times. The early time free streaming expansion is modified and receives logarithmic mass corrections induced by the shear-bulk couplings. The global flow structure and numerical analyses carried out in our work demonstrate the existence of the early and late-time attractors for the shear viscous tensor and bulk viscous pressure.

physics.flu-dyn↗

arXiv2022

All-order Resurgence from Complexified Path Integral in a Quantum Mechanical System with Integrability

We discuss all-order transseries in one of the simplest quantum mechanical systems: a U(1) symmetric single-degree-of-freedom system with a first-order time derivative term. Following the procedure of the Lefschetz thimble method, we explicitly evaluate the path integral for the generating function of the Noether charge and derive its exact transseries expression. Using the conservation law, we find all the complex saddle points of the action, which are responsible for the non-perturbative effects and the resurgence structure of the model. The all-order power-series contributions around each saddle point are generated from the one-loop determinant with the help of the differential equations obeyed by the generating function. The transseries are constructed by summing up the contributions from all the relevant saddle points, which we identify by determining the intersection numbers between the dual thimbles and the original path integration contour. We confirm that the Borel ambiguities of the perturbation series are canceled by the non-perturbative ambiguities originating from the discontinuous jumps of the intersection numbers. The transseries computed in the path-integral formalism agrees with the exact generating function, whose explicit form can be obtained in the operator formalism thanks to the integrable nature of the model. This agreement indicates the non-perturbative completeness of the transseries obtained by the semi-classical expansion of the path integral based on the Lefschetz thimble method.

hep-th↗

arXiv2021

Exact-WKB analysis for SUSY and quantum deformed potentials: Quantum mechanics with Grassmann fields and Wess-Zumino terms

Quantum deformed potentials arise naturally in quantum mechanical systems of one bosonic coordinate coupled to $N_f$ Grassmann valued fermionic coordinates, or to a topological Wess-Zumino term. These systems decompose into sectors with a classical potential plus a quantum deformation. Using exact WKB, we derive exact quantization condition and its median resummation. The solution of median resummed form gives physical Borel-Ecalle resummed results, as we show explicitly in quantum deformed double- and triple- well potentials. Despite the fact that instantons are finite action, for generic quantum deformation, they do not contribute to the energy spectrum at leading order in semi-classics. For certain quantized quantum deformations, where the alignment of levels to all order in perturbation theory occurs, instantons contribute to the spectrum. If deformation parameter is not properly quantized, their effect disappears, but higher order effects in semi-classics survive. In this sense, we classify saddle contributions as fading and robust. Finally, for quantum deformed triple-well potential, we demonstrate the P-NP relation, by computing period integrals and Mellin transform.

hep-th↗

arXiv2021

Constraining the initial stages of ultrarelativistic nuclear collisions

It is frequently supposed that quark-gluon plasma created in heavy-ion collisions undergoes free streaming at early times. We examine this issue based on the assumption that a universal attractor dominates the dynamics already at the earliest stages, which offers a way to connect the initial state with the start of the hydrodynamic expansion in an approximate but conceptually transparent fashion. We demonstrate that the centrality dependence of the measured particle multiplicities can be used to quantitatively constrain the pressure anisotropy and find that it strongly depends on the model of the initial energy deposition. As an illustration, we compare three initial state models and show that they predict rather different early-time values of the pressure anisotropy. This strongly suggests that assuming free streaming prior to hydrodynamization is not necessarily compatible with a generic initial state model and that features of the pre-hydrodynamic flow need to be matched with the model of the initial state.

nucl-th↗

arXiv2021

Quantum phase transition and Resurgence: Lessons from 3d $\mathcal{N}=4$ SQED

We study a resurgence structure of a quantum field theory with a phase transition to uncover relations between resurgence and phase transitions. In particular, we focus on three-dimensional $\mathcal{N}=4$ supersymmetric quantum electrodynamics (SQED) with multiple hypermultiplets, where a second-order quantum phase transition has been recently proposed in the large-flavor limit. We provide interpretations of the phase transition from the viewpoints of Lefschetz thimbles and resurgence. For this purpose, we study the Lefschetz thimble structure and properties of the large-flavor expansion for the partition function obtained by the supersymmetric localization. We show that the second-order phase transition is understood as a phenomenon where a Stokes and anti-Stokes phenomenon occurs simultaneously. The order of the phase transition is determined by how saddles collide at the critical point. In addition, the phase transition accompanies an infinite number of Stokes phenomena due to the supersymmetry. These features are appropriately mapped to the Borel plane structures as the resurgence theory expects. Given the lessons from the SQED, we provide a more general discussion on the relationship between the resurgence and phase transitions. In particular, we show how the information on the phase transition is decoded from the Borel resummation technique.

hep-th↗

arXiv2021

Exact-WKB, complete resurgent structure, and mixed anomaly in quantum mechanics on $S^1$

We investigate the exact-WKB analysis for quantum mechanics in a periodic potential, with $N $ minima on $S^{1}$. We describe the Stokes graphs of a general potential problem as a network of Airy-type or degenerate Weber-type building blocks, and provide a dictionary between the two. The two formulations are equivalent, but with their own pros and cons. Exact-WKB produces the quantization condition consistent with the known conjectures and mixed anomaly. The quantization condition for the case of $N$-minima on the circle factorizes over the Hilbert sub-spaces labeled by discrete theta angle (or Bloch momenta), and is consistent with 't Hooft anomaly for even $N$ and global inconsistency for odd $N$. By using Delabaere-Dillinger-Pham formula, we prove that the resurgent structure is closed in these Hilbert subspaces, built on discrete theta vacua, and by a transformation, this implies that fixed topological sectors (columns of resurgence triangle) are also closed under resurgence.

quant-ph↗

arXiv2020

On exact-WKB analysis, resurgent structure, and quantization conditions

There are two well-known approaches to studying nonperturbative aspects of quantum mechanical systems: Saddle point analysis of the partition functions in Euclidean path integral formulation and the exact-WKB analysis based on the wave functions in the Schrödinger equation. In this work, based on the quantization conditions obtained from the exact-WKB method, we determine the relations between the two formalism and in particular show how the two Stokes phenomena are connected to each other: the Stokes phenomenon leading to the ambiguous contribution of different sectors of the path integral formulation corresponds to the change of the "topology" of the Stoke curves in the exact-WKB analysis. We also clarify the equivalence of different quantization conditions including Bohr-Sommerfeld, path integral and Gutzwiller's ones. In particular, by reorganizing the exact quantization condition, we improve Gutzwiller analysis in a crucial way by bion contributions (incorporating complex periodic paths) and turn it into an exact result. Furthermore, we argue the novel meaning of quasi-moduli integral and provide a relation between the Maslov index and the intersection number of Lefschetz thimbles.

hep-th↗