arXiv subjects

Shin Sasaki

Publications and source records attributed to Shin Sasaki.

At least 19 recordsLinked to original sources

arXiv2026

Chiral Soliton Lattices under Magnetic Fields and Rotation: a Holographic Analysis

We study the chiral soliton lattice (CSL) in rotating QCD matter under a background magnetic field within holographic QCD. We show that rotation can be incorporated as a background gauge field and that the CSL in rotating matter becomes a ground state in the gravity dual. We also provide a brane interpretation of the CSL under a magnetic field and rotation. Solving the bulk equations, we derive an effective Hamiltonian where the meson decay constant $\tilde{f}$ emerges as an anisotropic, field-dependent matrix. Furthermore, we discuss the thermodynamic properties of the ground state in rotating matter and study its equation of state.

hep-th↗

arXiv2026

Mega-Space Current Algebra and Green-Schwarz Geometry in Heterotic String Theory

We study the Lorentz and gauge connections in heterotic string theories within a framework of manifest T-duality. A central motivation is the Bergshoeff--de Roo (BdR) type parallelism between the torsionful Lorentz and Yang-Mills connections in heterotic $\alpha'$-corrections. We formulate worldsheet current algebras in a mega-space that incorporates the Lorentz and gauge sectors simultaneously. By generalizing the Pol\'a\v{c}ek-Siegel scheme, we evaluate the commutators of the extended generators and determine the generalized connections. We show that this mega-space current algebra geometrically embeds the heterotic Chern--Simons structures into the generalized vielbeins and curvatures. We also show that the Green-Schwarz anomaly cancellation condition follows from the Jacobi identity for the algebra of stringy covariant derivatives, the ``nachos'' operators $\triangleright_{\mathcal{M}}$.

hep-th↗

arXiv2026

Revisiting the Wess-Zumino-Witten Term in Nuclear and Quark Matter under Magnetic Fields and Rotation

We study anomalous Wess-Zumino-Witten terms associated with the chiral anomaly in dense QCD matter under magnetic fields and rotation. By introducing electromagnetic, baryon number, and isospin background gauge fields, we write down the topological couplings of neutral mesons for the $N_f=2$ and $N_f=3$ cases. The resulting terms contain characteristic contributions proportional to $\vec{B} \cdot \vec{\nabla} \phi$ and $\vec{\Omega} \cdot \vec{\nabla} \phi$, where $\phi$ denotes $\pi^0$, $\eta$, or $\eta'$. These results are relevant to chiral soliton lattices in dense rotating matter.

hep-th↗

arXiv2026

Gauge-Dressed Complex Geometry and T-duality in Heterotic String Theories

We study T-duality of $(p,q)$-hermitian geometries in backgrounds with non-Abelian gauge fields $A$ in heterotic string theories. We introduce a gauge-dressed complex geometry characterized by a shifted metric $\bar{g} = g + \frac{1}{2} \mathrm{Tr}(A^2)$, the closed 2-form $\omega$ and a quasi complex structure satisfying $\bar{J}^2 < 0$, but not necessarily $\bar{J}^2 = -1$. Utilizing the positive and negative chirality half generalized complex-like structures constructed by $(\bar{g}, \bar{J})$, we derive a heterotic Buscher-like rule for geometric quantities. We also demonstrate that the gauge-dressed structures can be used to construct an extended Born geometry that satisfies algebras of hypercomplex numbers.

hep-th↗

arXiv2025

Quantum Electron Clouds near Black Holes: Black Atoms and Molecules

We study quantum mechanical wavefunctions near highly curved spaces, i.e., black holes. By utilizing the formalism developed by DeWitt, we derive the Schr\"odinger equations in the vicinity of the Schwarzschild and the Reissner-Nordstr\"om black hole geometries. The quantum electron cloud for the "black hydrogen atom" - an electron trapped by black holes - is particularly studied. We solve the equations and find that black holes generally attract the wavefunctions, localizing them near the horizon where the electrons are most likely to be trapped. These results imply that not only classical objects but also the quantum material and even the chemical properties of the atoms are affected by strong gravity. We also discuss black hydrogen molecules composed of multi-centered Majumdar-Papapetrou black holes.

gr-qc↗

arXiv2025

Holographic QCD Matter: Chiral Soliton Lattices in Strong Magnetic Field

We investigate the chiral soliton lattice (CSL) in the framework of holographic QCD in magnetic field. Under appropriate boundary conditions for the gauge field and the quark mass deformation, we demonstrate that the ground state in the gravitational dual of QCD is given by the CSL in the background magnetic field and the baryon number density. In the presence of the background magnetic field, we show that the CSL is interpreted as a uniformly distributed D4-branes in the holographic setup, where the chiral soliton is identified with a non-self-dual instanton vortex or a center vortex in the five dimensional bulk gauge theory. While the baryon numbers are given to chiral solitons as well as Skyrmions due to the different terms in the Wess-Zumino-Witten (WZW) term in the chiral perturbation theory, these baryon numbers with different origins are unified in terms of the instanton charge density in five dimensions. With bulk analysis of the WZW term, we find that the pion decay constant becomes dependent on the magnetic field. For the massless pion case, we obtain an analytical form that is in qualitative agreement with lattice QCD results for strong magnetic fields.

hep-th↗

arXiv2025

Electric-Magnetic Duality for Symmetric Tensor Gauge Theories and Immobile $p$-branes

We study electric-magnetic duality in Lorentz invariant symmetric tensor gauge theories, where immobile charged particles - fractons - arise due to the generalized current conservation $\partial_{\mu} \partial_{\nu} J^{\mu \nu} = 0$ and the fracton gauge principle. We show that the duality in the symmetric gauge theories holds only in four-dimensional spacetime. In higher dimensions, the duality does not hold with only the symmetric gauge fields but tensor fields with more complex symmetries come into play. Furthermore, we show that a hierarchy for the symmetric gauge field theories of higher ranks is interpreted by the bi-form calculus. We also discuss the restricted immobility of $p$-branes in the mixed symmetric gauge theories. As a byproduct, we find that novel self-duality conditions are defined as BPS equations in the four-dimensional Euclidean space.

hep-th↗

arXiv2024

T-duality on Almost Hermitian Spaces

We investigate T-duality transformation on an almost bi-hermitian space with torsion. By virtue of the Buscher rule, we completely describe not only the covariant derivative of geometrical objects but also the Nijenhuis tensor. We apply this description to an almost bi-hermitian space with isometry and investigate integrability on its T-dualized one. We find that hermiticity is not a sufficient condition to preserve integrability under T-duality transformations. However, in the presence of the K\"{a}hler condition, the T-dualized space still admits integrability of the almost complex structures. We also observe that the form of H-flux is suitable for string compactification scenarios.

hep-th↗

arXiv2024

Extended Doubled Structures of Algebroids for Gauged Double Field Theory

We study an analogue of the Drinfel'd double for algebroids associated with the $O(D,D+n)$ gauged double field theory (DFT). We show that algebroids defined by the twisted C-bracket in the gauged DFT are built out of a direct sum of three (twisted) Lie algebroids. They exhibit a "tripled", which we call the extended double, rather than the "doubled" structure appeared in (ungauged) DFT. We find that the compatibilities of the extended doubled structure result not only in the strong constraint but also the additional condition in the gauged DFT. We establish a geometrical implementation of these structures in a $(2D+n)$-dimensional product manifold and examine the relations to the generalized geometry for heterotic string theories and non-Abelian gauge symmetries in DFT.

hep-th↗

arXiv2024

Solitonic ground state in supersymmetric theory in background

A solitonic ground state called a chiral soliton lattice (CSL) is realized in a supersymmetric theory with background magnetic field and finite chemical potential. To this end, we construct, in the superfield formalism, a supersymmetric chiral sine-Gordon model as a neutral pion sector of a supersymmetric two-flavor chiral Lagrangian with a Wess-Zumino-Witten term. The CSL ground state appears in the presence of either a strong magnetic field and/or large chemical potential, or a background fermionic condensate in the form of a fermion bilinear consisting of the gaugino and a superpartner of a baryon gauge field.

hep-th↗

arXiv2024

On Geometries and Monodromies for Branes of Codimension Two

We study geometries for the NS5-, the KK5- and the $5^2_2$-branes of codimension two in type II and heterotic string theories. The geometries are classified by monodromies that each brane has. They are the $B$-, the general coordinate and the $β$-transformations of the spacetime metric, the $B$-field and the dilaton (and the gauge fields). We show that the monodromy nature appears also in the geometric quantities such as the curvature and the complex structures of spacetime. They are linearly realized in the doubled (generalized) structures in the doubled space.

hep-th↗

arXiv2023

Complex Structures, T-duality and Worldsheet Instantons in Born Sigma Models

We investigate doubled (generalized) complex structures in $2D$-dimensional Born geometries where T-duality symmetry is manifestly realized. We show that Kähler, hyperkähler, bi-hermitian and bi-hypercomplex structures of spacetime are implemented in Born geometries as doubled structures. We find that the Born structures and the generalized Kähler (hyperkähler) structures appear as subalgebras of bi-quaternions and split-tetra-quaternions. We find parts of these structures are classified by Clifford algebras. We then study the T-duality nature of the worldsheet instantons in Born sigma models. We show that the instantons in Kähler geometries are related to those in bi-hermitian geometries in a non-trivial way.

hep-th↗

arXiv2023

Worldsheet Instanton Corrections to Five-branes and Waves in Double Field Theory

We make a comprehensive study on the string winding corrections to supergravity solutions in double field theory (DFT). We find five-brane and wave solutions of diverse codimensions in which the winding coordinates are naturally included. We discuss a physical interpretation of the winding coordinate dependence. The analysis based on the geometric structures behind the solutions leads to an interpretation of the winding dependence as string worldsheet instanton corrections. We also give a brief discussion on the origins of these winding corrections in gauged linear sigma model. Our analysis reveals that for every supergravity solution, one has DFT solutions that include string winding corrections.

hep-th↗

arXiv2023

Gauged Double Field Theory, Current Algebras and Heterotic Sigma Models

We study the $O(D,D+n)$ generalized metric and the gauge symmetries in the gauged double field theory (DFT) in view of current algebras and sigma models. We show that the $O(D,D+n)$ generalized metric in the gauged DFT is consistent with the heterotic sigma models at the leading order in the $α'$-corrections. We then study the non-Abelian gauge symmetries and current algebras of heterotic string theories. We show that the algebras exhibit the correct diffeomorphism, the $B$-field gauge transformations of the background fields together with the non-Abelian gauge transformations possibly with the appropriate local Lorentz transformations.

hep-th↗

arXiv2022

Vacua by Derivative Corrections in $\mathcal{N}=1$ Supergravity with Matter Multiplets

We study the vacuum structures of four-dimensional $\mathcal{N} = 1$ old minimal supergravity with higher derivative corrections. We find that $\mathcal{N} = 1$ supergravity with Riemann curvature square corrections and higher derivative matter chiral multiplets induces a non-trivial de Sitter vacuum, even in the absence of superpotentials. This vacuum generically breaks supersymmetry. We show that the auxiliary fields in the gravity and the chiral multiples play important roles to generate a potential in supersymmetric higher derivative theories.

hep-th↗

arXiv2022

Modeling photometric variations due to a global inhomogeneity on an obliquely rotating star: application to lightcurves of white dwarfs

We develop a general framework to compute photometric variations induced by the oblique rotation of a star with an axisymmetric inhomogeneous surface. We apply the framework to compute lightcurves of white dwarfs adopting two simple models of their surface inhomogeneity. Depending on the surface model and the location of the observer, the resulting lightcurve exhibits a departure from a purely sinusoidal curve that are observed for a fraction of white dwarfs. As a specific example, we fit our model to the observed phase-folded lightcurve of a fast-spinning white dwarf ZTF J190132.9+145808.7 (with the rotation period of 419s). We find that the size and obliquity angle of the spot responsible for the photometric variation are $\dts \approx 60^\circ$ and $\thetaS \approx 60^\circ$ or $90^\circ$, respectively, implying an interesting constraint on the surface distribution of the magnetic field on white dwarfs.

astro-ph.SR↗

arXiv2022

Hyperkähler, Bi-hypercomplex, Generalized Hyperkähler Structures and T-duality

We investigate comprehensive relations among T-duality, complex and bi-hermitian structures $(J_+, J_-)$ in two-dimensional $\mathcal{N} =(2,2)$ sigma models with/without twisted chiral multiplets. The bi-hermitian structures $(J_+,J_-)$ embedded in generalized Kähler structures $(\mathcal{J}_+,\mathcal{J}_-)$ are organized into the algebra of the tri-complex numbers. We newly write down an analogue of the Buscher rule by which the T-duality transformation of the bi-hermitian and Kähler structures are apparent. We also study the bi-hypercomplex and hyperkähler cases in $\mathcal{N} = (4,4)$ theories. They are expressed, as a T-duality covariant fashion, in the generalized hyperkähler structures and form the split-bi-quaternion algebras. As a concrete example, we show the explicit T-duality relation between the hyperkähler structures of the KK-monopole (Taub-NUT space) and the bi-hypercomplex structures of the H-monopole (smeared NS5-brane). Utilizing this result, we comment on a T-duality relation for the worldsheet instantons in these geometries.

hep-th↗

arXiv2022

Analytic model for photometric variation due to starspots on a differentially rotating star

We present an analytic model of the lightcurve variation for stars with non-evolving starspots on a differentially rotating surface. The Fourier coefficients of the harmonics of the rotation period are expressed in terms of the latitude of the spot, $\ell_{s}$, and the observer's line-of-sight direction, $\ell_{o}$, including the limb darkening effect. We generate different realizations of multi-spots according to the model, and perform mock observations of the resulting lightcurve modulations. We discuss to what extent one can recover the properties of the spots and the parameters for the differential rotation law from the periodogram analysis. Although our analytical model neglects the evolution of spots on the stellar surface (dynamical motion, creation and annihilation), it provides a basic framework to interpret the photometric variation of stars, in particular from the existing Kepler data and the future space-born mission. It is also applicable to photometric modulations induced by rotation of various astronomical objects.

astro-ph.SR↗