Papers - Yamamoto, Naoki

Quantum Hall liquids in high-density QCD

Kentaro Nishimura, Naoki Yamamoto, Ryo Yokokura

Physical Review D 111 ( 5 ) 054010(1-7) 2025.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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There exist metastable domain walls of the flavor-singlet meson η for the U(1) axial symmetry in two-flavor color superconductivity (2SC) in quantum chromodynamics (QCD) at large baryon density. We show that, due to the coupling of η to confined SU(2) gluons in the 2SC phase, the effective theory on the domain wall is described by the SU(2)-1 Chern-Simons theory, which is dual to the U(1)2 Chern-Simons theory. This theory has a spin-1 droplet excitation that does not carry a baryon number, which we identify as a vector meson. We also discuss the effective theories and baryonic droplet excitations on the domain walls of the flavor-singlet mesons in the superfluid phases of QCD at large isospin density and two-color QCD at large baryon density.

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Chiral kinetic theory with self-energy corrections and neutrino spin Hall effect

Naoki Yamamoto, Di-Lun Yang

Physical Review D 109 ( 5 ) 056010(1-14) 2024.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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We systematically derive the chiral kinetic theory for chiral fermions with collisions, including the self-energy corrections, from quantum field theories. We find that the Wigner functions and chiral kinetic equations receive both the classical and quantum corrections from the self-energies and their spacetime gradients. We also apply this formalism to study nonequilibrium neutrino transport due to the interaction with thermalized electrons and nucleons, as realized in core-collapse supernovae. We derive neutrino currents along magnetic fields and neutrino spin Hall effect induced by the density gradient at first order in the Fermi constant GF for anisotropic neutrino distributions.

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Convergence of Ginzburg–Landau Expansions: Superconductivity in the Bardeen–Cooper–Schrieffer Theory and Chiral Symmetry Breaking in the Nambu–Jona-Lasinio Model

William Gyory, Naoki Yamamoto

Progress of Theoretical and Experimental Physics (The Physical Society of Japan)  2024 ( 4 ) 043D01(1-19) 2024.03

Research paper (scientific journal), Joint Work, Accepted

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We study the convergence of the Ginzburg–Landau (GL) expansion in the context of the Bardeen–Cooper–Schrieffer (BCS) theory for superconductivity and the Nambu–Jona-Lasinio (NJL) model for chiral symmetry breaking at finite temperature T and chemical potential μ. We present derivations of the all-order formulas for the coefficients of the GL expansions in both systems under the mean-field approximation. We show that the convergence radii for the BCS gap ∆ and dynamical quark mass M are given by ∆conv = πT and Mconv = √μ2 + (πT)2, respectively. We also discuss the implications of these results and the quantitative reliability of the GL expansion near the first-order chiral phase transition.

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Dipole symmetries from the topology of the phase space and the constraints on the low-energy spectrum

Tomáš Brauner, Naoki Yamamoto, Ryo Yokokura

SciPost Physics 16 ( 2 ) 051:1 - 051:32 2024.02

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate the general existence of a local dipole conservation law in bosonic field theory. The scalar charge density arises from the symplectic form of the system, whereas the tensor current descends from its stress tensor. The algebra of spatial translations becomes centrally extended in presence of field configurations with a finite nonzero charge. Furthermore, when the symplectic form is closed but not exact, the system may, surprisingly, lack a well-defined momentum density. This leads to a theorem for the presence of additional light modes in the system whenever the short-distance physics is governed by a translationally invariant local field theory. We also illustrate this mechanism for axion electrodynamics as an example of a system with Nambu–Goldstone modes of higher-form symmetries.

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Chiral asteroseismology: seismic oscillations caused by chiral transport in neutron stars and supernovae

Sota Hanai, Naoki Yamamoto

Journal of Cosmology and Astroparticle Physics 10 ( 018 ) 1 - 25 2023.10

Research paper (scientific journal), Joint Work, Accepted

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We study the novel asteroseismology of the chiral magnetic wave (CMW) of the quark number density in relativistic quark matter inside neutron stars and core-collapse supernovae and the chiral vortical wave (CVW) of the neutrino number density in relativistic neutrino matter at the core of supernovae. We call the oscillation modes for these chiral waves the chiral magnetic mode (CM-mode) and chiral vortical mode (CV-mode), respectively. We derive the dispersion relations of these new modes in the presence of the chirality flipping due to the finite quark mass and diffusion. We then estimate the possible frequencies of these modes and amplitudes of the resulting gravitational waves. In particular, since the CM-mode can exist only in quark matter with nearly gapless quarks (such as the two-flavor color superconductivity) for a sufficiently strong magnetic field, corresponding gravitational waves provide a new possible probe for such quark matter and the magnetic field in neutron stars.

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Generalized chiral instabilities, linking numbers, and non-invertible symmetries

Naoki Yamamoto, Ryo Yokokura

Journal of High Energy Physics 07 ( 45 ) 1 - 29 2023.07

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate a universal mechanism of a class of instabilities in infrared regions for massless Abelian p-form gauge theories with topological interactions, which we call generalized chiral instabilities. Such instabilities occur in the presence of initial electric fields for the p-form gauge fields. We show that the dynamically generated magnetic fields tend to decrease the initial electric fields and result in configurations with linking numbers, which can be characterized by non-invertible global symmetries. The so-called chiral plasma instability and instabilities of the axion electrodynamics and (4+1)-dimensional Maxwell-Chern-Simons theory in electric fields can be described by the generalized chiral instabilities in a unified manner. We also illustrate this mechanism in the (2+1)-dimensional Goldstone-Maxwell model in electric field.

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Effective Chiral Magnetic Effect from Neutrino Radiation

Naoki Yamamoto, Di-Lun Yang

Physical Review Letters 131 ( 1 ) 012701(1-6) 2023.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00319007

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We develop an approach to chiral kinetic theories for electrons close to equilibrium and neutrinos away from equilibrium based on a systematic power counting scheme for different timescales of electromagnetic and weak interactions. Under this framework, we derive electric and energy currents along magnetic fields induced by neutrino radiation in general nonequilibrium states. This may be regarded as an effective chiral magnetic effect (CME), which is present without a chiral chemical potential, unlike the conventional CME. We also consider the so-called gain region of core-collapse supernovae as an example and find that the effective CME enhanced by persistent neutrino emission in time is sufficiently large to lead to the inverse cascade of magnetic and fluid kinetic energies and observed magnitudes of pulsar kicks. Our framework may also be applicable to other dense-matter systems involving nonequilibrium neutrinos.

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Chiral effects in astrophysics and cosmology

Kohei Kamada, Naoki Yamamoto, Di-Lun Yang

Progress in Particle and Nuclear Physics 129   104016 2023.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01466410

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The microscopic quantum nature of elementary particles, chirality, leads to macroscopic phenomena like the chiral anomaly, chiral magnetic effect, and chiral plasma instability. We review recent progress of the studies of these chiral effects in high-energy astrophysics, such as pulsar kicks, magnetars, and core-collapse supernovae, and early Universe cosmology, such as the primordial magnetic field, baryogenesis, and chiral gravitational waves. We also provide a pedagogical introduction to the chiral effects and low-energy effective theories to describe them in and out of equilibrium—the chiral (magneto)hydrodynamics, chiral kinetic theory, and chiral radiation transport theory for neutrinos.

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Unstable Nambu-Goldstone modes

Naoki Yamamoto, Ryo Yokokura

Physical Review D 106 ( 10 ) 105004(1-9) 2022.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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Nambu-Goldstone (NG) modes for 0-form and higher-form symmetries can become unstable in the presence of background fields. Examples include the instability of a photon with a time-dependent axion background or with a chirality imbalance, known as the chiral plasma instability, and the instability of a dynamical axion with a background electric field. We show that all these phenomena can be universally described by a symmetry algebra for 0-form and higher-form symmetries. We prove a counting rule for the number of unstable NG modes in terms of correlation functions of broken symmetry generators. Based on our unified description, we further give a simple new example where one of the NG modes associated with the spontaneous 0-form symmetry breaking U(1)×U(1)→{1} becomes unstable.

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Chiral gravitational waves from thermalized neutrinos in the early Universe

Philipp Gubler, Naoki Yamamoto, Di-Lun Yang

Journal of Cosmology and Astroparticle Physics 09 ( 025 ) 1 - 36 2022.09

Research paper (scientific journal), Joint Work, Accepted

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We investigate polarized gravitational waves generated by chiral fermions in the early Universe. In particular, we focus on the contribution from left-handed neutrinos in thermal equilibrium with finite temperature and chemical potential in the radiation dominated era. We compute the correlation functions of gravitational fields pertinent to the Stokes parameter V characterizing the circular polarization of gravitational waves in the Minkowski and expanding spacetime backgrounds. In the expanding universe, we find that the thermalized neutrinos induce a non-vanishing V linear to the neutrino degeneracy parameter and wavenumber of gravitational waves in the long wavelength region. While the magnitude of the gravitational waves generated by thermal neutrinos is too small to be detectable by current and planned third generation gravitational wave detectors, their observations by future generation detectors for ultra-high frequency regimes could provide information on the neutrino degeneracy parameter in the early Universe.

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Chiral plasma instability and inverse cascade from nonequilibrium left-handed neutrinos in core-collapse supernovae

Jin Matsumoto, Naoki Yamamoto, Di-Lun Yang

Physical Review D 105 ( 12 ) 123029(1-7) 2022.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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We show that the backreaction of left-handed neutrinos out of equilibrium on the matter sector induces an electric current proportional to a magnetic field even without a chiral imbalance for electrons in core-collapse supernovae. We derive the transport coefficient of this effect based on the recently formulated chiral radiation transport theory for neutrinos. This chiral electric current generates a strong magnetic field via the so-called chiral plasma instability, which could provide a new mechanism for the strong and stable magnetic field of magnetars. We also numerically study the physical origin of the inverse cascade of the magnetic energy in the magnetohydrodynamics including this current. Our results indicate that incorporating the chiral effects of neutrinos would drastically modify the hydrodynamic evolutions of supernovae, which may also be relevant to the explosion dynamics.

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Photonic spin Hall effect from quantum kinetic theory in curved spacetime

Kazuya Mameda, Naoki Yamamoto, Di-Lun Yang

Physical Review D 105 ( 9 ) 096019(1-9) 2022.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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Based on quantum field theory, we formulate the Wigner function and quantum kinetic theory for polarized photons in curved spacetimes which admit a covariantly constant timelike vector. From this framework, the photonic chiral/zilch vortical effects are reproduced in a rigidly rotating coordinate. In a spatially inhomogeneous coordinate, we derive the spin Hall effect for the photon helicity current and energy current in equilibrium. Our derivation reveals that such photonic Hall effect are related to the photonic vortical effect via the Lorentz invariance and their transport coefficients match each other.

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Magnetic field induced neutrino chiral transport near equilibrium

Naoki Yamamoto, Di-Lun Yang

Physical Review D 104 ( 12 ) 123019(1-15) 2021.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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Based on the recently formulated chiral radiation transport theory for left-handed neutrinos, we study the chiral transport of neutrinos near thermal equilibrium in core-collapse supernovae. We first compute the near-equilibrium solution of the chiral radiation transport equation under the relaxation time approximation, where the relaxation time is directly derived from the effective field theory of the weak interaction. By using such a solution, we systematically derive analytic expressions for the nonequilibrium corrections of the neutrino energy-momentum tensor and neutrino number current induced by magnetic fields via the neutrino absorption on nucleons. In particular, we find the nonequilibrium neutrino energy current proportional to the magnetic field. We also discuss its phenomenological consequences such as the possible relation to pulsar kicks.

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Chiral soliton lattice phase in warm QCD

Tomáš Brauner, Helena Kolešová, Naoki Yamamoto

Physics Letters B 823 ( 10 ) 136767(1-7) 2021.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  03702693

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We analyze the phase diagram of quantum chromodynamics at low-to-moderate temperature, baryon chemical potential and external magnetic field within chiral perturbation theory at next-to-leading order of the derivative expansion. Our main result is that the anomaly-induced chiral soliton lattice (CSL) phase is stabilized by thermal fluctuations. As a consequence, the CSL state may survive up to temperatures at which chiral symmetry is restored.

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Floquet vacuum engineering: Laser-driven chiral soliton lattice in the QCD vacuum

Akihiro Yamada, Naoki Yamamoto

Physical Review D 104 ( 5 ) 054041(1-7) 2021.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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What happens to the QCD vacuum when a time-periodic circularly polarized laser field with a sufficiently large intensity and frequency is applied? Based on the Floquet formalism for periodically driven systems and the systematic low-energy effective theory of QCD, we show that for a sufficiently large frequency and above a critical intensity, the QCD vacuum is unstable against the chiral soliton lattice of pions; a crystalline structure of topological solitons that spontaneously breaks parity and continuous translational symmetries. Our work would pave the way for novel “Floquet vacuum engineering.”

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Positive magnetoresistance induced by hydrodynamic fluctuations in chiral media

Noriyuki Sogabe, Naoki Yamamoto, Yi Yin

Journal of High Energy Physics 09 ( 131 ) 1 - 31 2021.09

Research paper (scientific journal), Joint Work, Accepted

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We analyze the combined effects of hydrodynamic fluctuations and chiral magnetic effect (CME) for a chiral medium in the presence of a background magnetic field. Based on the recently developed non-equilibrium effective field theory, we show fluctuations give rise to a CME-related positive contribution to magnetoresistance, while the early studies without accounting for the fluctuations find a CME-related negative magnetoresistance. At zero axial relaxation rate, the fluctuations contribute to the transverse conductivity in addition to the longitudinal one.

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Topological mass generation in gapless systems

Naoki Yamamoto, Ryo Yokokura

Physical Review D 104 ( 2 ) 025010(1-17) 2021.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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Mass generation of gauge fields can be universally described by topological couplings in gapped systems, such as the Abelian Higgs model in (3+1) dimensions and the Maxwell-Chern-Simons theory in (2+1) dimensions. These systems also exhibit the spontaneous breaking of higher-form Zk symmetries and topological orders for level k≥2. In this paper, we consider topological mass generation in gapless systems. As a paradigmatic example, we study the axion electrodynamics with level k in (3+1) dimensions in background fields that hosts both gapped and gapless modes. We argue that the gapped mode is related to those in fully gapped systems in lower dimensions via dimensional reduction. We show that this system exhibits the spontaneous breaking of a higher-form Zk symmetry despite the absence of the conventional topological order. In the case of the background magnetic field, we also derive the low-energy effective theory of the gapless mode with the quadratic dispersion relation and show that it satisfies the chiral anomaly matching.

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Helical magnetic effect and the chiral anomaly

Naoki Yamamoto, Di-Lun Yang

Physical Review D 103 ( 12 ) 125003(1-7) 2021.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24700010

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In the presence of the fluid helicity v·ω, the magnetic field induces an electric current of the form j=C_{HME}(v·ω)B. This is the helical magnetic effect (HME). We show that for massless Dirac fermions with charge e=1, the transport coefficient CHME is fixed by the chiral anomaly coefficient C=1/(2π^2) as C_{HME}=C/2 independently of interactions. We show the conjecture that the coefficient of the magnetovorticity coupling for the local vector charge, n=CBωB·ω, is related to the chiral anomaly coefficient as CBω=C/2. We also discuss the condition for the emergence of the helical plasma instability that originates from the HME.

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Wigner functions and quantum kinetic theory of polarized photons

Koichi Hattori, Yoshimasa Hidaka, Naoki Yamamoto, Di-Lun Yang

Journal of High Energy Physics 02 ( 1 ) 1 - 26 2021.02

Research paper (scientific journal), Joint Work, Accepted

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We derive the Wigner functions of polarized photons in the Coulomb gauge with the ħ expansion applied to quantum field theory, and identify side-jump effects for massless photons. We also discuss the photonic chiral vortical effect for the Chern-Simons current and zilch vortical effect for the zilch current in local thermal equilibrium as a consistency check for our formalism. The results are found to be in agreement with those obtained from different approaches. Moreover, using the real-time formalism, we construct the quantum kinetic theory (QKT) for polarized photons. By further adopting a specific power counting scheme for the distribution functions, we provide a more succinct form of an effective QKT. This photonic QKT involves quantum corrections associated with self-energy gradients in the collision term, which are analogous to the side-jump corrections pertinent to spin-orbit interactions in the chiral kinetic theory for massless fermions. The same theoretical framework can also be directly applied to weakly coupled gluons in the absence of background color fields.

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Topological term, QCD anomaly, and the η′ chiral soliton lattice in rotating baryonic matter

Kentaro Nishimura, Naoki Yamamoto

Journal of High Energy Physics 07 ( 196 ) 1 - 23 2020.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  11266708

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We study the ground states of low-density hadronic matter and high-density color-flavor locked color superconducting phase in three-flavor QCD at finite baryon chemical potential under rotation. We find that, in both cases under sufficiently fast rotation, the combination of the rotation-induced topological term for the η′ meson and the QCD anomaly leads to an inhomogeneous condensate of the η′ meson, known as the chiral soliton lattice (CSL). We find that, when baryon chemical potential is much larger than isospin chemical potential, the critical angular velocity for the realization of the η′ CSL is much smaller than that for the π0 CSL found previously. We also argue that the η′ CSL states in flavor-symmetric QCD at low density and high density should be continuously connected, extending the quark-hadron continuity conjecture in the presence of the rotation.

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