Low-energy Sector Research Articles

The q-Schwarzian and Liouville gravity

We present a new holographic duality between q-Schwarzian quantum mechanics and Liouville gravity. The q-Schwarzian is a one parameter deformation of the Schwarzian, which is dual to JT gravity and describes the low energy sector of SYK. We show that the q-Schwarzian in turn is dual to sinh dilaton gravity. This one parameter deformation of JT gravity can be rewritten as Liouville gravity. We match the thermodynamics and classical two point function between q-Schwarzian and Liouville gravity. We further prove the duality on the quantum level by rewriting sinh dilaton gravity as a topological gauge theory, and showing that the latter equals the q-Schwarzian. As the q-Schwarzian can be quantized exactly, this duality can be viewed as an exact solution of sinh dilaton gravity on the disk topology. For real q, this q-Schwarzian corresponds to double-scaled SYK and is dual to a sine dilaton gravity.

Can Transport Infrastructure Improve Enterprise Energy Efficiency? Evidence From China

As an advanced social development capital, transportation plays a vital role in promoting regional development. Concurrently, the business activities of enterprises intimately relate to these transportation services. Utilizing road construction to improve the energy efficiency of enterprises, therefore, becomes a critical way to promote the transformation of the economy from high-speed development to high-quality development. Existing studies primarily focus on the impact of transport infrastructure on productivity, while few papers focus on the impact mechanism of transport infrastructure on energy efficiency. To delve deeper into the internal relationship between transportation and regional economic development, this paper explores the effect of transport infrastructure on energy utilization efficiency at the enterprise level. Based on the environmental pollution data of Chinese industrial enterprises from 2001 to 2011, this paper analyzes the impact of transport infrastructure on enterprises’ energy efficiency and verifies the impact mechanism. The results show that the construction and improvement of urban road facilities can significantly improve firm energy utilization efficiency. Compared to low-energy consumption sectors, the impact of transportation infrastructure on the energy efficiency of high-energy consumption industry enterprises is notably more pronounced. A closer examination of the impact mechanism revealed that both industrial agglomeration and the cost effect are pivotal mechanisms through which transportation infrastructure affects enterprise energy efficiency. JEL Classification: D21, L91, Q40, Q51

Supersymmetry dictated topology in periodic gauge fields and realization in strained and twisted 2D materials

Supersymmetry (SUSY) of a Hamiltonian dictates double degeneracy between a pair of superpartners (SPs) transformed by supercharge, except at zero energy where modes remain unpaired in many cases. Here we explore a SUSY of complete isospectrum between SPs-with paired zero modes-realized by 2D electrons in zero-flux periodic gauge fields, which can describe twisted or periodically strained 2D materials. We find their low-energy sector containing zero (or threshold) modes must be topologically non-trivial, by proving that Chern numbers of the two SPs have a finite difference dictated by the number of zero modes and energy dispersion in their vicinity. In 30° twisted bilayer (double bilayer) transition metal dichalcogenides subject to periodic strain, we find one SP is topologically trivial in its lowest miniband, while the twin SP of identical dispersion has a Chern number of 1 (2), in stark contrast to time-reversal partners that have to be simultaneously trivial or nontrivial. For systems whose physical Hamiltonian corresponds to the square root of a SUSY Hamiltonian, such as twisted or strained bilayer graphene, we reveal that topological properties of the two SUSY SPs are transferred respectively to the conduction and valence bands, including the contrasted topology in the low-energy sector and identical topology in the high-energy sector. This offers a unified perspective for understanding topological properties in many flat-band systems described by such square-root models. Both types of SUSY systems provide unique opportunities for exploring correlated and topological phases of matter.

Rotating black holes in a viable Lorentz-violating gravity: finding exact solutions without tears

We introduce a two-step procedure for finding Kerr-type rotating black hole solutions without tears. Considering the low-energy sector of Hořava gravity as a viable Lorentz-violating gravity in four dimensions which admits a different speed of gravity, we find the exact rotating black hole solutions (with or without cosmological constant). We find that the singular region extends to r<0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r<0$$\\end{document} region from the ring singularity at r=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r=0$$\\end{document} in Boyer–Lindquist coordinates. There are two Killing horizons where grr=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g^{rr}=0$$\\end{document} and the black hole thermodynamics laws are still valid. We find the rotating black hole solutions with electromagnetic charges only when we consider the noble electromagnetic couplings, in such a way that the speed of light is the same as the speed of gravity. With the noble choice of couplings, our Lorentz-violating gravity can be consistent with the recently-observed time delay of the coincident GW and GRB signals. Furthermore, in Appendices, we show that (a) the uniqueness of the invariant line element ds2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ds^2$$\\end{document} under the foliation-preserving diffeomorphism DiffF\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${ Diff}_\\mathcal{F}$$\\end{document}, contrary to Lorentz-violating action, (b) the solutions are the Petrov type I with four distinct principal null vectors, and (c) the Hamilton-Jacobi equation for the geodesic particles are not separable.

(Almost) everything is a Dicke model - Mapping non-superradiant correlated light-matter systems to the exactly solvable Dicke model

We investigate classes of interacting quantum spin systems in a single-mode cavity with a Dicke coupling, as a paradigmatic example of strongly correlated light-matter systems. Coming from the limit of weak light-matter couplings and large number of matter entities, we map the relevant low-energy sector of a broad class of models in the non-superradiant phases onto the exactly solvable Dicke model. We apply the outcomes to the Dicke-Ising model as a paradigmatic example [Phys. Rev. Res. 2, 023131 (2020), Sci. Rep. 4, 4083 (2014)], in agreement with results obtained by mean-field theory [Sci. Rep. 4, 4083 (2014)]. We further accompany and verify our findings with finite-size calculations, using exact diagonalization and the series expansion method pcst^{++}++ [Phys. Rev. A 108, 013323 (2023)]

Double-gluon charmonium hybrid states with various exotic quantum numbers

We study the double-gluon charmonium hybrid states with various quantum numbers, each of which is composed of one valence charm quark and one valence charm antiquark as well as two valence gluons. We concentrate on the exotic quantum numbers JPC=0−−/0+−/1−+/2+−/3−+ that the conventional q¯q mesons cannot reach. We apply the QCD sum rule method to calculate their masses to be 7.28−0.43+0.38, 5.19−0.46+0.36, 5.46−0.62+0.41, 4.48−0.31+0.25, and 5.54−0.43+0.35 GeV, respectively. We study their possible decay patterns and propose to search for the JPC=2+−/3−+ states in the D*D¯(*)/Ds*D¯s(*)/Σc*Σ¯c(*)/Ξc*Ξ¯c(′,*) channels. Experimental investigations on these states and decay channels can be useful in classifying the nature of the hybrid state, thus serving as a direct test of QCD in the low energy sector. Published by the American Physical Society 2024

Job creation in a low carbon transition to renewables and energy efficiency: a review of international evidence

AbstractIn this paper, we present findings from a systematic review on job creation, quality, and skills, focusing on decarbonisation in the energy sector. We compare a range of gross job employment factors which indicate that overall, investment in renewable energy and energy efficiency can deliver more jobs than gas or coal power generation. In addition, we review a subset of recent studies which estimate the net employment effects of decarbonisation in the energy sector at a national scale, across various international contexts. These national studies largely agree that the most likely outcome over the next few decades is a modest net positive creation of jobs and moderate economic growth. In certain regions within these countries, jobs in fossil fuel industries may be lost faster than the pace at which low carbon energy sectors can offer new employment. There may be mismatches between regions where displaced workers live and where new opportunities become available, which may be a barrier to accepting alternative employment even if former workers have the requisite skills. In these cases national government transition plans are recommended, coordinated with local governments, to manage the impacts of displacement from carbon-intensive sectors and respond to the need to build a new low carbon workforce including through skills development and training. We highlight a lack of metrics and data in the literature on job quality, skills, and the geographic distribution of employment impacts in decarbonising energy systems, and these should be priority areas for further research.

Evaluating the symmetric and asymmetric effectiveness of low carbon energy consumption for ecological footprint in China: the role of environment-related technological innovation.

The objective of this study is to scrutinize the impact of low carbon energy consumption, environmental-related technological innovation, urbanization, economic growth, and trade on China's ecological footprint from 1980 to 2021. To investigate the nature of the long-term connections between the variables, we employ the symmetric and asymmetric autoregressive distributed lag (ARDL) technique to explore the long- and short-run elasticities of coefficients. The results of ARDL and NARDL verified the environmental Kuznets curve (EKC) hypothesis in the long run in the presence of low carbon energy consumption. Moreover, the findings show that the positive part of low carbon energy consumption is negatively connected with the ecological footprint. Alternatively, the positive part of low carbon energy consumption is positively linked with the ecological footprint. The outcome highlights that environment-related technological innovation reduces the level of ecological footprint. Similarly, urbanization has a detrimental effect on the ecological footprint. Based on the estimated findings, it is suggested that China's economy should place a greater emphasis on increasing its level of investment in the low carbon energy sector and adopting severe environmental legislation to protect the economy from environmental burden.

Hilbert space structure and classical limit of the low energy sector of U(N) quantum Hall ferromagnets

Using the Lieb–Mattis ordering theorem of electronic energy levels, we identify and construct the Hilbert space of the low energy sector of U(N) quantum Hall/Heisenberg ferromagnets at filling factor M for L Landau/lattice sites. The carrier Hilbert space of irreducible representations of U(N) is described by rectangular Young tableaux of M rows and L columns, and associated with Grassmannian phase spaces U(N)/U(M)×U(N-M). Replacing U(N)-spin operators by their expectation values in a Grassmannian coherent state allows for a semi-classical treatment of the low energy U(N)-spin-wave coherent excitations (skyrmions) of U(N) quantum Hall ferromagnets in terms of Grasmannian nonlinear sigma models.

Cross-dimensional valley excitons from Förster coupling in arbitrarily twisted stacks of monolayer semiconductors

In stacks of transition metal dichalcogenide monolayers with arbitrary twisting angles, we explore a new class of bright excitons arising from the pronounced Förster coupling, whose dimensionality is tuned by its in-plane momentum. The low energy sector at small momenta is two-dimensional, featuring a Mexican Hat dispersion, while the high energy sector at larger momenta becomes three-dimensional (3D) with sizable group velocity both in-plane and out-of-plane. By choices of the spacer thickness, versatile surface or interface exciton modes localized at designated layers can emerge out of the cross-dimensional bulk dispersion for a topological origin, which can be mapped to the Su–Schrieffer–Heeger soliton. Moreover, step-edges in spacers can be exploited for engineering lateral interfaces to enable interlayer communication of the topological interface exciton. Combined with the polarization selection rule inherited from the monolayer building block, these exotic exciton properties open up new opportunities for multilayer design towards 3D integration of valley exciton optoelectronics.

A microscopic model of black hole evaporation in two dimensions

We present a microscopic model of black hole (BH) ‘evaporation’ in asymptotically AdS2 spacetimes dual to the low energy sector of the SYK model. To describe evaporation, the SYK model is coupled to a bath comprising of Nf free scalar fields Φi. We consider a linear combination of couplings of the form OSY K(t)∑iΦi(0, t), where OSY K involves products of the Kourkoulou-Maldacena operator iJ/N{sum}_{k=1}^{N/2}{s}_k^{prime }{psi}_{2k-1}(t){psi}_{2k}(t) specified by a spin vector s′. We discuss the time evolution of a product of (i) a pure state of the SYK system, namely a BH microstate characterized by a spin vector s and an effective BH temperature TBH, and (ii) a Calabrese-Cardy state of the bath characterized by an effective temperature Tbath. We take Tbath ≪ TBH, and TBH much lower than the characteristic UV scale J of the SYK model, allowing a description in terms of the time reparameterization mode. Tracing over the bath degrees of freedom leads to a Feynman-Vernon type effective action for the SYK model, which we study in the low energy limit. The leading large N behaviour of the time reparameterization mode is found, as well as the Oleft(1/sqrt{N}right) fluctuations. The latter are characterized by a non-Markovian non-linear stochastic differential equation with non-local Gaussian noise. In a restricted range of couplings, we find two classes of solutions which asymptotically approach (a) a BH at a lower temperature, and (b) a horizonless geometry. We identify these with partial and complete BH evaporation, respectively. Importantly, the asymptotic solution in both cases involves the scalar product of the spin vectors s.s′, which carries some information about the initial state. By repeating the dynamical process O(N2) times with different choices of the spin vector s′, one can in principle reconstruct the initial BH microstate.

Noncommutative $$SO(2,3)_{\star }$$ gauge theory of gravity

Topological gravity (in the sense that it is metric-independent) in a 2n-dimensional spacetime can be formulated as a gauge field theory for the AdS gauge group $$SO(2,2n-1)$$ by adding a multiplet of scalar fields. These scalars can break the gauge invariance of the topological gravity action, thus making a connection with Einstein’s gravity. This review is about a noncommutative (NC) star-product deformation of the four-dimensional AdS gauge theory of gravity, including Dirac spinors and the Yang–Mills field. In general, NC actions can be expanded in powers of the canonical noncommutativity parameter $$\theta$$ using the Seiberg–Witten map. The leading-order term of the expansion is the classical action, while the higher-order $$\theta$$ -dependent terms are interpreted as new types of coupling between classical fields due to spacetime noncommutativity. We study how these perturbative NC corrections affect the field equations of motion and derive some phenomenological consequences, such as NC-deformed Landau levels of an electron. Finally, we discuss how topological gravity in four dimensions (both classical and noncommutative) appears as a low-energy sector of five-dimensional Chern–Simons gauge theory in the sense of Kaluza–Klein reduction.

Are cities venturing green? A global analysis of the impact of green entrepreneurship on city air pollution

Situated at the intersection between environmental entrepreneurship and urban sustainability, our paper seeks to investigate the links between city-level green venture ecosystems and the ability of urban centres to reduce air pollution. Using a large dataset of 12,834 urban centres from around the world and their associated yearly average particulate matter (PM2.5), we show that an increase in the cumulative number of green start-ups drives the lowering of PM2.5 levels. Looking closely at the subsectors that drive the results, we observe that the urban centres which hosted increased numbers of innovators in smart grid technologies, energy efficiency and wind energy generation (the low carbon energy sector overall) also experienced a decrease in air pollution over the 2010–2019 period. Thus, our study is a global analysis of the environmental impact of green entrepreneurship on local air pollution.

QFT without infinities and hierarchy problem

The standard way to do computations in Quantum Field Theory (QFT) often results in the requirement of dramatic cancellations between contributions induced by a “heavy” sector into the physical observables of the “light” (or low energy) sector – the phenomenon known as “technical hierarchy problem”. This procedure uses divergent multi-loop Feynman diagrams, their regularisation to handle the UV divergences, and then renormalisation to remove them. At the same time, the ultimate outcome of the renormalisation is the mapping of several finite parameters defining the renormalisable field theory into different observables (e.g. all kinds of particle cross-sections). In this paper, we first demonstrate how to relate the parameters of the theory to observables without running into intermediate UV divergences. Then we go one step further: we show how in theories with different mass scales, all physics of the “light” sector can be computed in a way that does not require dramatic cancellations induced by the physics of the “heavy” sector. The existence of such a technique suggests that the “hierarchy problem” in renormalisable theories is not really physical, but rather an artefact of the conventional procedure to compute correlation functions. If the QFT is defined by the “divergencies-free” method all fine-tunings in theories with well-separated energy scales may be avoided.

Scalar-singlet assisted leptogenesis with CP violation from the vacuum

In the vanilla type-I seesaw leptogenesis scenario, CP violation required to generate the lepton asymmetries in the heavy Majorana neutrino decays stem from complex Dirac-type Yukawa couplings. In this paper we explore the case in which that CP violation originates from the vacuum expectation value of a complex scalar singlet at a very high scale. This non-trivial CP-violating phase can be successfully communicated to the low-energy neutrino sector via the heavy neutrino portal. The new scalar-singlet degrees of freedom generate new contributions to the CP asymmetries relevant for leptogenesis not only at the one-loop level but also through tree-level three-body decays. These are computed here for an arbitrary number of heavy neutrinos, Higgs doublets and scalar singlets. We also take into account the new decays and scattering processes that enter the unflavoured Boltzmann equations governing the heavy-neutrino particle densities and the (B – L)-asymmetry evolution. Having established the framework of interest, we present a simple model with two RH neutrinos, two Higgs doublets and a complex scalar singlet, supplemented with a Ƶ8 flavour symmetry. This symmetry minimises the number of free parameters without compromising the possibility of spontaneous CP violation and compatibility with neutrino data. In fact, the only viable Ƶ8 charge assignment shows a preference for a non-trivial spontaneous CP-violating phase, which in turn leads to a non-vanishing CP asymmetry due to the direct link between high- and low-energy CP violation. An interesting feature of this simple setup is that the usual wave and vertex type-I seesaw contributions to the CP asymmetry vanish due to the Ƶ8 symmetry. Thus, the observed baryon-to-photon ratio can be explained thanks to the new couplings among the heavy neutrinos and the new scalar degrees of freedom.

Emergence of the spin polarized domains in the kagome lattice Heisenberg antiferromagnet Zn-barlowite (Zn0.95Cu0.05)Cu3(OD)6FBr

Kagome lattice Heisenberg antiferromagnets are known to be highly sensitive to perturbations caused by the structural disorder. NMR is a local probe ideally suited for investigating such disorder-induced effects, but in practice, large distributions in the conventional one-dimensional NMR data make it difficult to distinguish the intrinsic behavior expected for pristine kagome quantum spin liquids from disorder-induced effects. Here we report the development of a two-dimensional NMR data acquisition scheme applied to Zn-barlowite (Zn0.95Cu0.05)Cu3(OD)6FBr kagome lattice, and successfully correlate the distribution of the low energy spin excitations with that of the local spin susceptibility. We present evidence for the gradual growth of domains with a local spin polarization induced by 5% Cu2+ defect spins occupying the interlayer non-magnetic Zn2+ sites. These spin-polarized domains account for ~60% of the sample volume at 2 K, where gapless excitations induced by interlayer defects dominate the low-energy sector of spin excitations within the kagome planes.

Emergent non-Abelian gauge theory in coupled spin-electron dynamics

A clear separation of the time scales governing the dynamics of "slow" and "fast" degrees of freedom often serves as a prerequisite for the emergence of an independent low-energy theory. Here, we consider (slow) classical spins exchange coupled to a tight-binding system of (fast) conduction electrons. The effective equations of motion are derived under the constraint that the quantum state of the electron system at any instant of time $t$ lies in the $n$-dimensional low-energy subspace for the corresponding spin configuration at $t$. The effective low-energy theory unfolds itself straightforwardly and takes the form of a non-abelian gauge theory with the gauge freedom given by the arbitrariness of the basis spanning the instantaneous low-energy sector. The holonomic constraint generates a gauge covariant spin-Berry curvature tensor in the equations of motion for the classical spins. In the non-abelian theory for $n>1$, opposed to the $n=1$ adiabatic spin dynamics theory, the spin-Berry curvature is generically nonzero, even for time-reversal symmetric systems. Its expectation value with the representation of the electron state is gauge invariant and gives rise to an additional {\em geometrical} spin torque. Besides anomalous precession, the $n\ge 2$ theory also captures the spin nutational motion, which is usually considered as a retardation effect. This is demonstrated by proof-of-principle numerical calculations for a minimal model with a single classical spin. Already for $n=2$ and in parameter regimes where the $n=1$ adiabatic theory breaks down, we find good agreement with results obtained from the full (unconstrained) theory.

Towards sustainable methane supply from local bioresources: Anaerobic digestion, gasification, and gas upgrading

Methane is a versatile and storable energy carrier, which is likely to play an important role in the European transition towards a low fossil carbon energy sector. We investigate the potentials for meeting regional methane demands through conversion of local residual bioresources for supply of bio-based CH4. We have developed a tiered assessment framework involving i) allocation of residual and constrained bioresources to conversion pathways based on physical and biochemical properties, ii) life cycle assessment (LCA) of technology conversion pathways through process-oriented parameterisation of the LCA model, and iii) LCA modelling of system-level technology implementation scenarios for quantification of regional potentials for bio-based CH4 supply and environmental savings, in view of current uses of the same bioresources. Two main technology conversion pathways are included: gasification and anaerobic digestion, both with hydrogen enhancement. The latter was also considered with water scrubbing upgrading. The framework is implemented for the French region, Occitania, with a residual bioresource potential of 48 TWh·y−1 (distributed on 41 different bioresources), and an annual methane demand of 17.5 TWh·y−1, currently supplied by natural gas. The assessment results clearly demonstrate that utilisation of available residual bioresources has tremendous potential both for covering current gas demands in the region (up to about seven times in some scenarios) but also for a reduction in climate change impacts from the region (up to about 37%).

Quantum sine-Gordon dynamics in coupled spin chains

The sine-Gordon field theory emerges as the low-energy description in a wealth of quantum many-body systems. Recent efforts have been directed towards realizing quantum simulators of the model, by interfering two weakly coupled one-dimensional cold atomic gases. The weak interactions within the atomic clouds provide a sine-Gordon realization in the semiclassical regime. Furthermore, the intricate microscopic dynamics prevents a quantitative understanding of the effective sine-Gordon validity realm. In this work, we focus on a spin-ladder realization and observe the emergent sine-Gordon dynamics deep in the quantum regime. We use matrix-product state techniques to numerically characterize the low-energy sector of the system and compare it with the exact field-theory predictions. From this comparison, we obtain quantitative boundaries for the validity of the sine-Gordon description. We provide encompassing evidence for the emergent field theory by probing its rich spectrum and by observing the signatures of integrable dynamics in scattering events.

Role of anomalous symmetry in 0−π qubits

We present an exact full symmetry analysis of the 0-$\pi$ superconducting circuit. We identify points in control parameter space of enhanced anomalous symmetry, which imposes robust twofold degeneracy of its ground state, that is for all values of the energy parameters of the model. We show, both analytically and numerically, how this anomalous symmetry is maintained in the low-energy sector, thus providing us with a strong candidate for robust qubit engineering.