Anomalous-magnetic-moment-enhanced Casimir effect

Fujii, Daisuke; Nakayama, Katsumasa*; Suzuki, Kei

Physical Review D, 113(3), p.036002_1 - 036002_12, 2026/02

https://doi.org/10.1103/6zds-1htp

We present a theoretical study on how the anomalous magnetic moment (AMM) of Dirac fermions influences the fermionic Casimir effect in the presence of magnetic fields. The analysis is carried out by generalizing the standard Lifshitz formula to incorporate the AMM. Our extended formulation reveals that the presence of the AMM leads to an increase in the fermionic Casimir energy. Notably, when the AMM becomes sufficiently large, this enhancement is markedly amplified due to the gapless nature of the lowest Landau level. We further provide quantitative estimates of the Casimir energy contributions from various fermions, such as electrons, muons, and constituent quarks, subjected to magnetic fields.

Holographic QCD matter in a bottom-up model

Fujii, Daisuke; Hosaka, Atsushi*; Iwanaka, Akihiro*; Sakai, Tadakatsu*; Tachibana, Motoi*

Proceedings of Science (Internet), 500, p.135_1 - 135_6, 2026/01

https://doi.org/10.22323/1.500.0135

Understanding strongly coupled QCD matter remains challenging due to its non-perturbative nature. We study finite-density, zero-temperature QCD in a two-flavor hard-wall holographic model with nonzero quark mass. The dense phase is obtained by solving the classical equations of motion under a homogeneous ansatz. To relate bulk fields to boundary observables, we perform holographic renormalization and construct the dictionary, emphasizing the essential role of an IR boundary term at the hard-wall cutoff. Within this setup we uncover a baryonic phase with large baryon number density and a strongly suppressed chiral condensate. From these solutions we derive the equation of state and compute neutron-star mass-radius relations, finding stars above two solar masses over a broad parameter range.

Scale-anomaly-induced binding pressure in hadrons

Fujii, Daisuke; Tanaka, Mitsuru*

Physics Letters B, 870, p.139872_1 - 139872_7, 2025/11

https://doi.org/10.1016/j.physletb.2025.139872

We investigate how the QCD scale anomaly contributes to the internal pressure structure of hadrons, employing the decomposition of the energy-momentum tensor into its trace and traceless parts. By utilizing recent model-independent results for gravitational form factors, we analyze the pressure distributions of both pions and nucleons in the instant form and the light-front form. Our analysis reveals that, in all examined cases, the confining pressure is predominantly driven by the scale anomaly. This indicates that the dominance of the scale anomaly in generating internal pressure is a robust and universal feature, regardless of the specific hadron, theoretical model, or form used in the analysis.

Lifshitz formulas for finite-density Casimir effect

Fujii, Daisuke; Nakayama, Katsumasa*; Suzuki, Kei

Physics Letters B, 868, p.139758_1 - 139758_6, 2025/09

https://doi.org/10.1016/j.physletb.2025.139758

The Lifshitz formula has long served as a foundational framework for analyzing the Casimir effect under finite-temperature conditions. In this work, we extend its applicability to situations involving finite chemical potential, thereby incorporating quantum field contributions beyond thermal effects. We illustrate the broad utility of the resulting generalized formula by exploring characteristic features of the Casimir effect across a variety of setups, including different boundary conditions, temperature regimes, spatial dimensionalities, and chemical potential imbalances. This extended framework is particularly relevant to systems such as dense quark matter and Dirac/Weyl semimetals, where the chemical potential functions as a tunable parameter that influences the Casimir force.

Dominance of gluonic scale anomaly in confining pressure inside nucleon and D-term

Fujii, Daisuke; Kawaguchi, Mamiya*; Tanaka, Mitsuru*

Physics Letters B, 866, p.139559_1 - 139559_7, 2025/07

https://doi.org/10.1016/j.physletb.2025.139559

We investigate the confining pressure inside the nucleon and the associated gravitational form factor, known as the D-term, within a skyrmion based on the scale-invariant chiral perturbation theory. In this approach, the effects of scale symmetry breaking are incorporated through the coupling of a scalar meson field to the scale anomaly, following the low-energy theorem. Utilizing the decomposition of the nucleon's energy-momentum tensor, we clarify how the scale anomaly components contribute to the internal pressure. Our analysis reveals that the gluon-induced scale anomaly predominantly governs the confining pressure. Compared to the result in the chiral limit of conventional chiral perturbation theory, this approach yields a total pressure profile more consistent with lattice QCD data. Furthermore, the pressure due to the gluonic anomaly extends over a wide spatial region, leading to a significant contribution to the D-term.

Casimir effect at finite density

Fujii, Daisuke; Nakayama, Katsumasa*; Suzuki, Kei

International Journal of Modern Physics A, 40(10-11), p.2543020_1 - 2543020_8, 2025/04

https://doi.org/10.1142/S0217751X25430201

In this talk, I discuss the general features of the Casimir effect induced from quantum fields at finite chemical potential, particularly at finite density. Historically, the thermal Casimir effect has been well-established by the cooperation between theory and experiment, whereas its counterpart at finite chemical potential is still not. This is because it is usually difficult to control the chemical potential of photons in equilibrium experimentally. On the other hand, if one focuses on fermionic systems, their chemical potentials may be a tunable parameter for the Casimir effect. In addition, various quantum many-body phenomena realized at finite fermion density can modify the typical property of the Casimir effect. Within some theoretical frameworks, we evaluate the Casimir energy for Dirac fields at finite density and particularly show an oscillatory behavior as a function of the separation of boundary conditions or the chemical potential. As physical and realistic examples of the Casimir effect at finite chemical potential, I discuss applications to fermion fields inside thin dense quark matter in hadron physics and to Dirac/Weyl semimetal thin films in solid-state physics. Such materials will be platforms to examine the fermionic Casimir effect at finite chemical potential.

Casimir effect on the lattice spacetime

Fujii, Daisuke; Nakayama, Katsumasa*; Suzuki, Kei

International Journal of Modern Physics A, 40(10-11), p.2543017_1 - 2543017_8, 2025/01

https://doi.org/10.1142/s0217751x25430171

We investigate the characteristics of Casimir energy within a lattice-regularized spacetime framework. Typically, Casimir energy requires a regularization procedure to remove divergences originating from vacuum fluctuations of quantum fields. In this work, we adopt lattice regularization, wherein discretization effects persist as long as the lattice spacing remains finite. We first detail how the Casimir energy is computed using both naive and Wilson fermion formulations. When discretization artifacts are limited to only a few lattice points, it becomes possible to recover the continuum Casimir energy by taking the continuum limit. To illustrate physical applications, we evaluate the Casimir energy for electron fields in Dirac/Weyl semimetals, where lattice effects are meaningfully retained, and for photon fields in axion electrodynamics, where the continuum limit is accurately reproduced.

Gravitational form factors of pion from top-down holographic QCD

Fujii, Daisuke; Iwanaka, Akihiro*; Tanaka, Mitsuru*

Physical Review D, 110(9), p.L091501_1 - L091501_8, 2024/11

https://doi.org/10.1103/PhysRevD.110.L091501

The gravitational form factors (GFFs) of pions are calculated from a top-down holographic quantum chromodynamics (QCD) approach with momentum transfer dependence for the first time. It is important because the GFFs of hadrons have information on the internal stress distribution that may provide insight into the mechanism of how QCD forms hadrons. The forward limit value of this GFFs, i.e. the D-term, was also obtained. Furthermore, in this approach, we observe the so-called glueball dominance, in which pions have gravitational interactions via infinite glueball spectra.

Electromagnetic transition amplitude for Roper resonance from holographic QCD

Fujii, Daisuke; Iwanaka, Akihiro*; Hosaka, Atsushi*

Physical Review D, 106(1), p.014010_1 - 014010_6, 2022/07

https://doi.org/10.1103/PhysRevD.106.014010

The Roper resonance, the first excited state of the nucleon, is one of the best established baryon resonates. Yet, its properties have not been consistently explained by effective models of QCD, such as the non-relativistic quark model. In this paper, we propose an alternative approach in the Sakai-Sugimoto model that is one of the holographic models of QCD. In particular, we analyze the helicity amplitude of the electromagnetic transitions at the leading of 't Hooft coupling . The model incorporates baryon structure at short distance by nonlinear mesons surrounded by meson clouds at long distance. We demonstrate that the recently observed data by CLAS are explained in the present approach.

Decay properties of Roper resonance in the holographic QCD

Fujii, Daisuke*; Hosaka, Atsushi

Physical Review D, 104(1), p.014022_1 - 014022_6, 2021/07

https://doi.org/10.1103/PhysRevD.104.014022