Fundamental Couplings Research Articles

Theoretical and observational implications of Planck’s constant as a running fine structure constant

This paper explores how a reinterpretation of the generalized uncertainty principle as an effective variation of Planck’s constant provides a physical explanation for a number of fundamental quantities and couplings. In this context, a running fine structure constant is naturally emergent and the cosmological constant problem is solved, yielding a novel connection between gravitation and quantum field theories. The model could potentially clarify the recent experimental observations by the DESI Collaboration that could imply a fading of dark energy over time. When applied to quantum systems and their characteristic length scales, a simple geometric relationship between energy and entropy is disclosed. Lastly, a mass–radius relation for both quantum and classical systems reveals a phase transition-like behavior similar to thermodynamical systems, which we speculate to be a consequence of topological defects in the universe.

Mathematical definition of the fine-structure constant: A clue for fundamental couplings in astrophysics

Astrophysical tests of the stability—or not—of fundamental couplings (e.g., can the numerical value ∼1/137 of the fine-structure constant α = e2/ℏc vary with astronomical time?) are a very active area of observational research. Using a specific α-free non-relativistic and nonlinear isotropic quantum model compatible with its quantum electrodynamics (QED) counterpart yields the 99% accurate solution α = 7.364 × 10−3 vs its experimental value 7.297 × 10−3. The ∼1% error is due to the deliberate use of mean-field Hartree approximation involving lowest-order QED in the calculations. The present theory has been checked by changing the geometry of the model. Moreover, it fits the mathematical solution of the original nonlinear integro-differential Hartree system by use of a rapidly convergent series of nonlinear eigenstates [G. Reinisch, Phys. Lett. A 498, 129347 (2024)]. These results strongly suggest the mathematical transcendental nature—e.g., like for π or e—of α’s numerical value of ∼1/137 and, hence, its astrophysical as well as its cosmological stability.

Tuning optical absorption in perovskite (K,Na)NbO3 ferroelectrics.

The ability to tailor the electronic band structure and optical absorption by appropriate cationic substitution in perovskite oxide ferroelectrics is essential for many advanced electronic and optoelectronic applications of these materials. Here, we explored weak (Ba,Ni)-doping for reducing optical bandgaps in (K,Na)NbO3 ferroelectric films and ceramics. The optical absorption in the broad spectral range of (0.7-8.8) eV was investigated in polycrystalline doped, pure, and oxygen deficient films, in doped epitaxial films grown on different substrates, and in doped ceramics. By comparing optical properties of all films and ceramics, it was established that 1-2 at% of cationic substitutions or up to 10 at % of oxygen vacancies have no detectable effect on the direct (∼4.5 eV) and indirect (∼3.9 eV) gaps. Concurrently, substantial sub-gap absorption was revealed and ascribed to structural band tailing in epitaxial films and ceramics. It was suggested that owing to fundamental strain-property couplings in perovskite oxide ferroelectrics, inhomogeneities of lattice strain can lead to increased sub-gap absorption. The uncovered structurally induced sub-gap optical absorption can be relevant for other ferroelectric ceramics and thin films as well as for related perovskite oxides.

Gauged SU(3)F and loop induced quark and lepton masses

We investigate a local SU(3)F flavour symmetry for its viability in generating the masses for the quarks and charged leptons of the first two families through radiative corrections. Only the third-generation fermions get tree-level masses due to specific choice of the field content and their gauge charges. Unprotected by symmetry, the remaining fermions acquire non-vanishing masses through the quantum corrections induced by the gauge bosons of broken SU(3)F. We show that inter-generational hierarchy between the masses of the first two families arises if the flavour symmetry is broken with an intermediate SU(2) leading to a specific ordering in the masses of the gauge bosons. Based on this scheme, we construct an explicit and predictive model and show its viability in reproducing the realistic charged fermion masses and quark mixing parameters in terms of not-so-hierarchical fundamental couplings. The model leads to the strange quark mass, ms ≈ 16 MeV at MZ, which is ~2.4σ away from its current central value. Large flavour violations are a generic prediction of the scheme which pushes the masses of the new gauge bosons to 103 TeV or higher.

Couplings of order six in the gauge field strength and the second fundamental form on Dp -branes at order α′2

Using the assumption that the independent gauge invariant couplings on the world-volume of the non-perturbative objects in the string theory are independent of the background, we find the four and the six gauge field strength and/or the second fundamental form couplings on the world volume of a D$_p$-brane in the superstring theory at order $\alpha'^2$ in the normalization that $F$ is dimensionless. We have found them by considering the particular background which has one circle and by imposing the corresponding T-duality constraint on the independent couplings. In particular, we find that there are 12+146 independent gauge invariant couplings at this order, and the T-duality constraint can fix 150 of them. We show that these couplings are fully consistent with the partial results in the literature. This comparison also fixes the remaining 8 couplings.

Constraining fundamental constant variations from ultralight dark matter with pulsar timing arrays

Pulsar Timing Arrays (PTAs) are exceptionally sensitive detectors in the frequency band $\text{nHz} \lesssim f \lesssim \mu\text{Hz}$. Ultralight dark matter (ULDM), with mass in the range $10^{-23}\,\text{eV} \lesssim m_\phi \lesssim 10^{-20}\,\text{eV}$, is one class of DM models known to generate signals in this frequency window. While purely gravitational signatures of ULDM have been studied previously, in this work we consider two signals in PTAs which arise in presence of direct couplings between ULDM and ordinary matter. These couplings induce variations in fundamental constants, i.e., particle masses and couplings. These variations can alter the moment of inertia of pulsars, inducing pulsar spin fluctuations via conservation of angular momentum, or induce apparent timing residuals due to reference clock shifts. By using mock data mimicking current PTA datasets, we show that PTA experiments outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons. In the case of coupling to quarks or photons, we find that PTAs and atomic clocks set similar constraints. Additionally, we discuss how future PTAs can further improve these constraints, and detail the unique properties of these signals relative to the previously studied effects of ULDM on PTAs.

Neutrino magnetic and electric dipole moments: From measurements to parameter space

Searches for neutrino magnetic moments/transitions in low energy neutrino scattering experiments are sensitive to effective couplings, which are an intricate function of the Hamiltonian parameters. We study the parameter space dependence of these couplings in the Majorana (transitions) and Dirac (moments) cases, as well as the impact of the current most stringent experimental upper limits on the fundamental parameters. In the Majorana case we find that for reactor, short-baseline, and solar neutrinos, $CP$ violation can be understood as a measurement of parameter space vectors misalignments. The presence of nonvanishing $CP$ phases opens a blind spot region where---regardless of how large the parameters are---no signal can be observed in either reactor or short-baseline experiments. Identification of these regions requires a combination of different datasets and allows for the determination of those $CP$ phases. We point out that stringent bounds not necessarily imply suppressed Hamiltonian couplings, thus allowing for regions where disparate upper limits can be simultaneously satisfied. In contrast, in the Dirac case stringent experimental upper limits necessarily translate into tight bounds on the fundamental couplings. In terms of parameter space vectors, we provide a straightforward mapping of experimental information into parameter space.

New Systematic Analysis Method of Identifying Microscopic Essential Couplings

We propose a systematic method of identifying essential model parameters for nonlinear response tensors. The analysis results reveal fundamental couplings in nontrivial responses and promote further development of multiferroic responses.

Equations and fundamental characteristics of compressional waves propagating in fluid-saturated porous materials

The main purpose of the paper is to present an extended analysis of the coupled system of linear equations describing compressional wave propagation in fluid-saturated porous materials, and to determine their fundamental characteristics. The present paper is a continuation of the analysis of equations for transverse waves that is presented in the manuscript (Cieszko and Kubik, 2020). The starting point of considerations in both works are nonlinear equations describing the dynamic behavior of the two-phase medium formulated in the spirit of the theory of interacting continua in which the parameters of an isotropic pore space structure are explicitly present in the model, and constitutive equations are formulated for each physical component (porous solid and fluid) separately. This system of equations contains all of the fundamental mechanical couplings between the components of such a medium in the general nonlinear form and of clear physical meaning. The linear coupled equations of this theory for a viscous barotropic fluid and a hyperelastic skeleton are equivalent to Biot's model, widely used in the description and analysis of wave propagation in saturated porous materials and wave interactions with the boundary of such media, and they are the subject of the ongoing analysis. A new method of analysis of the system of differential equations written in matrix form is proposed, based on the spectral decomposition of this system in the vector space of dilatations of the solid and fluid particles, and on the method of differential operator decomposition. Such an approach enabled to obtain two separated differential equations describing the propagation of two attenuated compressional waves called the fast and slow wave. This also allowed expressions for parameters characterizing both elastic compressional waves to be derived: velocities, effective mass densities and elastic modules, and also wave impedances which have been determined for the first time for saturated porous materials. In turn, the separated equations for attenuated waves enabled direct derivation of the dispersion equations for the plane harmonic waves of both types and determination of their frequency characteristics, i.e. phase velocities and attenuation coefficients. The obtained frequency characteristics of the fast and slow waves are fully defined by their velocities in the elastic and in the compact medium, and the coefficient characterizing the viscous interaction of the fluid with the skeleton. The results show that the phase velocity of the long slow wave can be greater than the phase velocity of the long fast wave, and the attenuation of the fast wave can be greater than attenuation of the slow wave. It was also proven that both waves can be anomalously dispersed which means that some porous materials saturated with fluid are metamaterials.

Light Absorption in Nanowire Photonic Crystal Slabs and the Physics of Exceptional Points: The Shape Shifter Modes.

Semiconductor nanowire arrays have been demonstrated as promising candidates for nanoscale optoelectronics applications due to their high detectivity as well as tunable photoresponse and bandgap over a wide spectral range. In the infrared (IR), where these attributes are more difficult to obtain, nanowires will play a major role in developing practical devices for detection, imaging and energy harvesting. Due to their geometry and periodic nature, vertical nanowire and nanopillar devices naturally lend themselves to waveguide and photonic crystal mode engineering leading to multifunctional materials and devices. In this paper, we computationally develop theoretical basis to enable better understanding of the fundamental electromagnetics, modes and couplings that govern these structures. Tuning the photonic response of a nanowire array is contingent on manipulating electromagnetic power flow through the lossy nanowires, which requires an intimate knowledge of the photonic crystal modes responsible for the power flow. Prior published work on establishing the fundamental physical modes involved has been based either on the modes of individual nanowires or numerically computed modes of 2D photonic crystals. We show that a unified description of the array key electromagnetic modes and their behavior is obtainable by taking into account modal interactions that are governed by the physics of exceptional points. Such models that describe the underlying physics of the photoresponse of nanowire arrays will facilitate the design and optimization of ensembles with requisite performance. Since nanowire arrays represent photonic crystal slabs, the essence of our results is applicable to arbitrary lossy photonic crystals in any frequency range.

Superallowed 0+→0+ nuclear β decays: 2020 critical survey, with implications for Vud and CKM unitarity

Superallowed $\ensuremath{\beta}$-decay between nuclear analog states with isospin 1 and spin-parity ${0}^{+}$ offers access to fundamental tests of the properties of the electroweak interaction. With 15 such transitions precisely measured, the data collectively probe the conservation of the weak vector current, set tight limits on the presence of beyond-standard-model scalar currents, and yield the most precise value for the ${V}_{u\phantom{\rule{0}{0ex}}d}$ element of the CKM quark-mixing matrix. ${V}_{u\phantom{\rule{0}{0ex}}d}$ is a critical ingredient required to test the unitarity of that matrix. This work provides an in-depth review of the relevant nuclear physics input and connects these data to the fundamental couplings.

Equations and fundamental characteristics of transverse waves propagating in fluid-saturated porous materials

The main purpose of the paper is to present an extended analysis of the coupled system of linear equations describing wave propagation in fluid-saturated porous materials used for the determination of their fundamental characteristics. The present paper is the first part, mainly devoted to the analysis of the system of equations describing transverse wave propagation. The analysis of equations for compressional waves will be presented in a separate paper. The starting point of considerations are nonlinear equations describing the dynamic behavior of the medium formulated in the spirit of the theory of interacting continua in which parameters of isotropic pore space structure are explicitly present in the model, and constitutive equations are formulated for each physical component separately. They contain all fundamental mechanical couplings between components of this medium in the general nonlinear form and of clear physical meaning. Linear equations of this theory for barotropic fluid and hyperelastic skeleton are the subject of the analysis performed in the paper. They are equivalent to Biot's model, widely used in the description and analysis of wave propagation in saturated porous materials and wave interaction with the boundary of such media. A new method of analysis is proposed in the paper, based on spectral decomposition of the system of equations in the two-dimensional vector space of rotations of solid and fluid particles. It is shown that each choice of the base in this vector space defines the division of the medium into two new components and transforms the system of equation to the form describing the dynamic behavior of these components, and the requirement of the basic dynamic properties of the medium to be invariant in each chosen base uniquely determines the mass densities and bulk modules of the new components. Such an approach enabled decomposition of the system of equations for particle rotations to two uncoupled scalar equations, the only one of which describes propagation of the transverse wave. This also allowed obtaining expressions characterizing transverse wave propagation in fluid-saturated porous materials: velocity, effective mass densities and wave impedance of the medium associated with this wave and its frequency characteristics: phase velocity and attenuation coefficient. It is shown that both frequency characteristics are fully defined by the effective mass densities of both components associated with the transverse wave, the tortuosity of the pore space, and the coefficient characterizing the viscous interaction of the fluid with the skeleton.

Electroweak baryogenesis from temperature-varying couplings

The fundamental couplings of the Standard Model are known to vary as a function of energy scale through the Renormalisation Group (RG), and have been measured at the electroweak scale at colliders. However, the variation of the couplings as a function of temperature need not be the same, raising the possibility that couplings in the early universe were not at the values predicted by RG evolution. We study how such temperature-variance of fundamental gauge couplings can aid the production of a baryon asymmetry in the universe through electroweak baryogenesis. We do so in the context of the Standard Model augmented by higher-dimensional operators up to dimension 6.

Cavity quantum-electrodynamical polaritonically enhanced electron-phonon coupling and its influence on superconductivity.

So far, laser control of solids has been mainly discussed in the context of strong classical nonlinear light-matter coupling in a pump-probe framework. Here, we propose a quantum-electrodynamical setting to address the coupling of a low-dimensional quantum material to quantized electromagnetic fields in quantum cavities. Using a protoypical model system describing FeSe/SrTiO3 with electron-phonon long-range forward scattering, we study how the formation of phonon polaritons at the two-dimensional interface of the material modifies effective couplings and superconducting properties in a Migdal-Eliashberg simulation. We find that through highly polarizable dipolar phonons, large cavity-enhanced electron-phonon couplings are possible, but superconductivity is not enhanced for the forward-scattering pairing mechanism due to the interplay between coupling enhancement and mode softening. Our results demonstrate that quantum cavities enable the engineering of fundamental couplings in solids, paving the way for unprecedented control of material properties.

Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant

There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\ensuremath{\alpha}$, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of $\ensuremath{\alpha}$ that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude.

Current and future white dwarf mass-radius constraints on varying fundamental couplings and unification scenarios

We discuss the feasibility of using astrophysical observations of white dwarfs as probes of fundamental physics. We quantify the effects of varying fundamental couplings on the white dwarf mass-radius relation in a broad class of unification scenarios, both for the simple case of a polytropic stellar structure model and for more general models. Independent measurements of the mass and radius, together with direct spectroscopic measurements of the fine-structure constant in white dwarf atmospheres lead to constraints on combinations of the two phenomenological parameters describing the underlying unification scenario (one of which is related to the strong sector of the theory while the other is related to the electroweak sector). While currently available measurements do not yet provide stringent constraints, we show that forthcoming improvements, expected for example from the Gaia satellite, can break parameter degeneracies and lead to constraints that ideally complement those obtained from local laboratory tests using atomic clocks.

Is there a connection between “dark” and “light” physics?

In the early-mid 20th century Dirac and Zel’dovich were among the first scientists to suggest an intimate connection between cosmology and atomic physics. Though a revolutionary proposal for its time, Dirac’s Large Number Hypothesis (1937) adopted a standard assumption of the day, namely, the non-existence of the cosmological constant term (Λ = 0). As a result, its implementation necessitated extreme violence to the theory of general relativity – something few physicists were prepared to sacrifice in favour of ‘numerology’ – requiring a time-dependent gravitational coupling of the form G(t) ∼ 1/t. Zel’dovich’s insight (1968) was to realise that a small but nonzero cosmological term (Λ > 0) allowed the present day radius of the Universe to be identified with the de Sitter radius, , which removed the need for time-dependence in the fundamental couplings. Thus, he obtained the formula Λ ≃ m6G2/ℏ4, where m is a mass scale characterising the relative strengths of the gravitational and electromagnetic interactions, which he identified with the proton mass mp. In this paper, we review a number of recent arguments which, instead, suggest the identification m = me/αe, where me is the electron mass and αe = e2/ℏc ≃ 1/137 is the usual fine structure constant. We note that these are of a physical nature and, therefore, represent an attempt to lift previous arguments à la Dirac from the realm of numerology into the realm of empirical science. If valid, such arguments suggest an intimate connection, not only between the macroscopic and microscopic worlds, but, perhaps even more surprisingly, between the very essence of “dark” and “light” physics.

Dark Energy Constraints from Espresso Tests of the Stability of Fundamental Couplings

ESPRESSO is a high-resolution-ultra-stable spectrograph for the Very Large Telescope (VLT), whose commissioning will start in 2017. One of its key science goals is to test the stability of nature’s fundamental couplings with unprecedented accuracy and control of possible systematics. A total of 27 nights of the ESPRESSO Consortium’s guaranteed time observations (GTO) will be spent on testing the stability of the fine-structure constant and other fundamental couplings. A set of 14 priority optimal targets have been selected for the GTO period. In this work, we discuss the criteria underlying this selection, describe the selected targets, and present some forecasts of the impact of these measurements on fundamental physics and cosmology, focusing on dark energy constraints and using future supernova type Ia surveys as a comparison point. This report is a summary of the results reported in Phys. Rev. D 2016, 94, 123512, to which we refer the reader for further details.

Stability of fundamental couplings: A global analysis

Astrophysical tests of the stability of fundamental couplings are becoming an increasingly important probe of new physics. Motivated by the recent availability of new and stronger constraints we update previous works testing the consistency of measurements of the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $\mu=m_p/m_e$ (mostly obtained in the optical/ultraviolet) with combined measurements of $\alpha$, $\mu$ and the proton gyromagnetic ratio $g_p$ (mostly in the radio band). We carry out a global analysis of all available data, including the 293 archival measurements of {\it Webb et al.} and 66 more recent dedicated measurements, and constraining both time and spatial variations. While nominally the full datasets show a slight statistical preference for variations of $\alpha$ and $\mu$ (at up to two standard deviations), we also find several inconsistencies between different sub-sets, likely due to hidden systematics and implying that these statistical preferences need to be taken with caution. The statistical evidence for a spatial dipole in the values of $\alpha$ is found at the 2.3 sigma level. Forthcoming studies with facilities such as ALMA and ESPRESSO should clarify these issues.

Effective Lagrangian in de Sitter spacetime

Scale invariant fluctuations of metric are universal feature of quantum gravity in de Sitter spacetime. We construct an effective Lagrangian which summarizes their implications on local physics by integrating super-horizon metric fluctuations. It shows infrared quantum effects are local and render fundamental couplings time dependent. We impose Lorenz invariance on the effective Lagrangian as it is required by the principle of general covariance. We show that such a requirement leads to unique physical predictions by fixing the quantization ambiguities. We explain how the gauge parameter dependence of observables is canceled. In particular the relative evolution speed of the couplings are shown to be gauge invariant.