Asia Pacific Center for Theoretical Physics

Non-Hermitian physics, such as the non-Hermitian skin effect (NHSE), is well-established in classical platforms, but its emergence in intrinsically Hermitian or quantum systems remains a key challenge. Bridging this gap is crucial for connecting non-Hermitian concepts with foundational quantum many-body theory. Here, we systematically investigate this by studying a quantum subsystem with an effective non-Hermitian Hamiltonian arising from its exact frequency-dependent self-energy. We further employ complex-frequency detection, including excitation, synthesis, and fingerprint, to probe physical responses induced by complex driving frequencies. Our calculations reveal that both complex frequency excitation and synthesis are incompatible with the non-Hermitian approximation and cannot characterize the presence of the NHSE. In contrast, the complex-frequency fingerprint successfully detects the distinctive responses induced by the NHSE through the introduction of a double-frequency Green’s function. Our work provides a platform for studying non-Hermitian physics and its unconventional response in quantum systems rigorously without relying on any approximations. Non-Hermitian physics, like the non-Hermitian skin effect (NHSE), is well-explored in classical platforms but remains challenging in quantum systems. Here, the authors study a quantum subsystem described by an effective non-Hermitian Hamiltonian derived from its exact frequency-dependent self-energy, and show that only complex-frequency fingerprinting can uniquely detect NHSE-induced responses, providing a rigorous framework for exploring non-Hermitian phenomena without approximation.

The relativistic momentum equation of a collisionless plasma is reformulated to describe the time evolution of canonical vorticity. Compared to the non-relativistic counterpart, an additional source term for canonical vorticity is identified, which embodies the misalignment between the fluid momentum and fluid velocity gradients. This kineclinic term breaks the frozen-in condition of canonical vorticity, thereby enabling generation or dissipation of magnetic fields and vorticity. We verify the role of this effect through particle-in-cell simulations of a modified Beltrami flow. Kineclinicity should be finite for all relativistic plasma systems due to the general lack of a functional relationship between fluid momentum and fluid velocity.

Diffusive motion is a fundamental transport mechanism in physical and biological systems, governing dynamics across a wide range of scales-from molecular transport to animal foraging. In many complex systems, however, diffusion deviates from classical Brownian behaviour, exhibiting striking phenomena such as Brownian yet non-Gaussian diffusion (BYNGD) and anomalous diffusion. BYNGD describes a frequently observed statistical feature characterised by the coexistence of linear mean-square displacement (MSD) and non-Gaussian displacement distributions. Anomalous diffusion, in contrast, involves a nonlinear time dependence of the MSD and often reflects mechanisms such as trapping, viscoelasticity, heterogeneity, or active processes. Both phenomena challenge the conventional framework based on constant diffusivity and Gaussian statistics. This review focuses on the theoretical modelling of such behaviour via the Langevin equation with fluctuating diffusivity (LEFD)-a flexible stochastic framework that captures essential features of diffusion in heterogeneous media. LEFD not only accounts for BYNGD but also naturally encompasses a wide range of anomalous transport phenomena, including subdiffusion, ageing, and weak ergodicity breaking. Ergodicity is discussed in terms of the correspondence between time and ensemble averages, as well as the trajectory-to-trajectory variability of time-averaged observables. The review further highlights the empirical relevance of LEFD and related models in explaining diverse experimental observations and underscores their value to uncovering the physical mechanisms governing transport in complex systems.

We study the Green's functions in non-Hermitian systems that exhibit the critical non-Hermitian skin effect (critical NHSE) using a double-chain Hatano-Nelson model with interchain coupling $\mathrm{\ensuremath{\Delta}}$. When $\mathrm{\ensuremath{\Delta}}=0$, the system decomposes into two independent chains and, in this case, the Green's functions follow predictable patterns based on the generalized Brillouin zone (GBZ) theory. For small $\mathrm{\ensuremath{\Delta}}$ $(\mathrm{\ensuremath{\Delta}}=1/10\phantom{\rule{0.16em}{0ex}}000)$, there are two cases. In conventional regions with trivial open-boundary conditions spectral winding numbers, the interchain coupling induces a zigzag scaling structure in the Green's functions, which can be explained by the first-order perturbation theory. In anomalous regions with nontrivial winding numbers, the actual Green's functions and the GBZ-based predictions match in the bulk but diverge near the boundaries and this deviation turns out to be derived from the influence of the GBZ of the $\mathrm{\ensuremath{\Delta}}=0$ case. These results reveal the unique nonperturbative features of the critical NHSE and highlight the limitations of the GBZ theory in capturing the boundary effects of finite-size systems and thus emphasize the need to consider both bulk and boundary dynamics in such systems.

We calculate the scalar-induced one-loop correction to the power spectrum of tensor perturbations produced during single-field slow-roll inflation. We find that the correction is given by the square of the product of the slow-roll parameter and the tree-level scalar power spetctrum. We also discuss the implications of the logarithmic contribution.

Understanding the mechanisms that sustain high biodiversity remains a central challenge. MacArthur's classical consumer-resource model (MCRM) suggests that consumer diversity is limited by the number of available resources, yet empirical observations often exceed this bound. To address this, we extend the generalized consumer-resource model by incorporating intraspecific suppression and analyze its effects using the dynamical mean-field theory. Our results show that intraspecific suppression promotes biodiversity by preventing the emergence of dominant species and enabling more species to coexist, particularly in resource-rich environments. Furthermore, our results provide analytical bounds on relative diversity, demonstrating that the number of coexisting consumer species can exceed the number of resource kinds. This highlights the critical role of intraspecific suppression and environmental factors in promoting coexistence.

Abstract This study investigates the thermoelectric (TE) properties of gallium boron nitride (GaB3N4) and its potential application in high-temperature thermoelectric generators (TEGs) from 1100 K to 2000K. Unlike the previous works on TEGs, we take into the account the variation in the Seebeck coefficient (α), electrical resistivity (ρ) and electronic thermal conductivity (κ) as the temperature varies along the p- and n-type legs of the TEG. This is done by obtaining the best fit curves of each TE parameters versus temperature and their corresponding equations. Then, we implement a slabbing approach where the p- and n-legs were divided into segments employing a 20 K increment. Using the best-fit equation, the intermediate values of α, ρ and κ across the p- and n- legs for the temperatures in between the cold and hot junctions were derived. The thermoelectric performance of the TEG such as electric current (I), voltage (V), power output (P), and efficiency (η) were then obtained, against the normalized load resistance (NLR). Our results showed that the GaB3N4-based TEG demonstrates superior high temperature TEG operation as higher values of I, V, P and η were achieved as temperature is increased from 1100 K to 2000 K. Finally, our findings suggest GaB3N4 exhibits competitive device efficiency as high as nearly 14% at 2000 K, thus making it a viable candidate for high-temperature TEG applications.

We construct a new dilaton Weyl multiplet for N=3 conformal supergravity in four dimensions. The R-symmetry realized on this dilaton Weyl multiplet is SU(2)×U(1)×U(1). The construction follows a two-step procedure. First, two on-shell vector multiplets are coupled to the standard Weyl multiplet. Second, using the field equations of the vector multiplets, some of the auxiliary fields of the standard Weyl multiplet are solved in terms of the fields belonging to the vector multiplets and some dual gauge fields. The remaining fields of the standard Weyl multiplet combine with the vector multiplet fields and the dual gauge fields to constitute the new dilaton Weyl multiplet. Published by the American Physical Society 2025