Conformal Gravity: Dark Matter and Dark Energy

This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Strict conformal symmetry (local Weyl scaling covariance), postulated for all elementary massless fields, retains standard fermion and gauge boson theory but modifies Einstein-Hilbert general relativity and the Higgs scalar field model, with no new physical fields. Subgalactic phenomenology is retained. Without invoking dark matter, conformal gravity and a conformal Higgs model fit empirical data on galactic rotational velocities, galactic halos, and Hubble expansion including dark energy.Comment: 9 pp in revtex format. References added with minor text revision

Conformal order and Poincareˊ\rm{\acute{e}}-Klein mapping underlying electrostatics-driven inhomogeneity in tethered membranes

Understanding the organization of matter under the long-range electrostatic force is a fundamental problem in multiple fields. In this work, based on the electrically charged tethered membrane model, we reveal regular structures underlying the lowest-energy states of inhomogeneously stretched planar lattices by a combination of numerical simulation and analytical geometric analysis. Specifically, we show the conformal order characterized by the preserved bond angle in the lattice deformation, and reveal the Poincar$\rm{\acute{e}}$-Klein mapping underlying the electrostatics-driven inhomogeneity. The discovery of the Poincar$\rm{\acute{e}}$-Klein mapping, which connects the Poincar$\rm{\acute{e}}$ disk and the Klein disk for the hyperbolic plane, implies the connection of long-range electrostatic force and hyperbolic geometry. We also discuss lattices with patterned charges of opposite signs for modulating in-plane inhomogeneity and even creating 3D shapes, which may have a connection to metamaterials design. This work suggests the geometric analysis as a promising approach for elucidating the organization of matter under the long-range force.Comment: 14 pages, 9 figure

Non-Hermitian Topological Magnonics

Dissipation in mechanics, optics, acoustics, and electronic circuits is nowadays recognized to be not always detrimental but can be exploited to achieve non-Hermitian topological phases or properties with functionalities for potential device applications. As elementary excitations of ordered magnetic moments that exist in various magnetic materials, magnons are the information carriers in magnonic devices with low-energy consumption for reprogrammable logic, non-reciprocal communication, and non-volatile memory functionalities. Non-Hermitian topological magnonics deals with the engineering of dissipation and/or gain for non-Hermitian topological phases or properties in magnets that are not achievable in the conventional Hermitian scenario, with associated functionalities cross-fertilized with their electronic, acoustic, optic, and mechanic counterparts, such as giant enhancement of magnonic frequency combs, magnon amplification, (quantum) sensing of the magnetic field with unprecedented sensitivity, magnon accumulation, and perfect absorption of microwaves. In this review article, we address the unified approach in constructing magnonic non-Hermitian Hamiltonian, introduce the basic non-Hermitian topological physics, and provide a comprehensive overview of the recent theoretical and experimental progress towards achieving distinct non-Hermitian topological phases or properties in magnonic devices, including exceptional points, exceptional nodal phases, non-Hermitian magnonic SSH model, and non-Hermitian skin effect. We emphasize the non-Hermitian Hamiltonian approach based on the Lindbladian or self-energy of the magnonic subsystem but address the physics beyond it as well, such as the crucial quantum jump effect in the quantum regime and non-Markovian dynamics. We provide a perspective for future opportunities and challenges before concluding this article.Comment: 101 pages, 35 figure

Phenomenology of the Lense-Thirring effect in the Solar System

Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate the present and future perspectives in directly measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in Astrophysics and Space Science (ApSS). Some uncited references in the text now correctly quoted. One reference added. A footnote adde

Anti-Reflective Dielectric Nanostructures for Solar Cells Analyzed from a Helicity Preservation Perspective

Continuing increase of carbon dioxide (CO$_2$) emissions and subsequent growth of the global average temperature pushes us towards a faster transition from fossil fuels to renewable energy sources. In this respect, photovoltaics (PV) may play a decisive role in achieving net zero CO$_2$ emissions within the desired time frame. While new PV technologies have been actively researched over recent years, silicon (Si) PV continues to dominate the world market. Despite the maturity of Si PV, there is still room for improvement. In particular, to keep up with the estimates for the global installed PV capacity for upcoming decades, one has to consider how much energy is actually used for manufacturing Si wafers. Thus, it is feasible to consider a transition to thinner Si absorbers. However, such transition requires adjustments of the industrially accepted processes used to negate optical losses since the standard approach employing random pyramidal textures is no longer feasible for rather thin wafers. Thus, alternative strategies have to be established. For this purpose, nanophotonic structures are of interest. In particular, dielectric scatterers supporting Mie resonances attracted attention from the research community over the last few years. In this thesis, we perform a holistic study of periodic and disordered anti-reflective (AR) dielectric nanostructures applied to crystalline silicon (c-Si) heterojunction (HJT) solar cells. We optimize the optical performance of these systems and show that the AR properties of the nanostructure arrays on top of solar cell stacks are related to two requirements: a sufficiently high degree of discrete rotational symmetry of an array and the ability to preserve helicity of the incident illumination. For a periodic system, the first condition can be readily met. The second condition generally requires the system to be made from materials with an equal electric permittivity and magnetic permeability. Since this is unfeasible with naturally available materials, this condition has to be relaxed. Indeed, similar effects can be achieved if only the electric and magnetic response from the photonic nanostructure is balanced. This balance is accomplished by tuning the geometrical parameters of scatterers made from high index materials. For a disordered system, the helicity preservation condition can be reduced similarly to a periodic system. However, in such a system, the first condition is not exactly applicable. Luckily, the disorder can be tailored such that it becomes stealthy hyperuniform, and large-scale density fluctuations are suppressed. Such tailored disordered patterns are fully isotropic, thus possessing effective continuous rotational symmetry. Therefore, the AR properties of these systems are also related to the requirements stated above. Furthermore, we fabricate solar cells coated with periodic and tailored disordered nanodisks based on the optimal designs. We characterize the optical and electrical properties of the samples and observe the improvement of the AR properties and subsequent positive influence on the short-circuit current density. A complementary analysis of the annual energy yield of the solar modules employing solar cells with nanodisk coatings shows that our designs can potentially be integrated into the module with their positive effect preserved