Higher-order Couplings Research Articles

Multiple reentrant phase transitions and triple points in Lovelock thermodynamics

We investigate the effects of higher curvature corrections from Lovelock gravity on the phase structure of asymptotically AdS black holes, treating the cosmological constant as a thermodynamic pressure. We examine how various thermodynamic phenomena, such as Van der Waals behaviour, reentrant phase transitions (RPT), and tricritical points are manifest for U(1) charged black holes in Gauss-Bonnet and 3rd-order Lovelock gravities. We furthermore observe a new phenomenon of ‘multiple RPT’ behaviour, in which for fixed pressure the small/large/small/large black hole phase transition occurs as the temperature of the system increases. We also find that when the higher-order Lovelock couplings are related in a particular way, a peculiar isolated critical point emerges for hyperbolic black holes and is characterized by non-standard critical exponents.

Planck scale, Higgs mass, and scalar dark matter

This study is inspired by a scenario, in which the Standard Model enhanced by an additional dark-matter scalar could be extended up to the Planck scale, while accommodating the low measured value of the Higgs mass. To that end, we study a toy model for a gauge-singlet dark-matter scalar coupled to the Higgs-top-quark sector of the Standard Model. Using functional methods to derive renormalization group flow equations in that model, we examine several choices for the ultraviolet, bare potential in the Higgs-dark-matter sector. Our results indicate that the dark-matter scalar can decrease the lower bound on the Higgs mass in the Standard Model. We then use the fact that higher-order couplings which are driven to tiny values by the renormalization group flow towards low energies can easily be of order one at the ultraviolet cutoff scale. Our study indicates that the inclusion of these couplings can significantly increase the ultraviolet cutoff scale and therefore the range of validity of the model while yielding a low value for the Higgs mass in the infrared. This is achieved within a setting where the dark-matter scalar accounts for the complete dark-matter relic density in our Universe.

Dynamic analysis of generally laminated composite beam with a delamination based on a higher-order shear deformable theory

In this study, the dynamic response of the laminated composite beam with arbitrary lay-ups has been investigated within the framework of the third-order shear deformation theory using the finite element method. A new three-nodded finite element compliant with the theory is introduced next. To deal with the dynamic contact between the delaminated segments, unilateral contact constraints are employed in conjunction with Lagrange multiplier method. Furthermore, the Poisson’s effect is incorporated in the formulation of the beam constitutive equation. Also, the higher-order inertia effects and material couplings (flexure–tensile, flexure–twist and tensile–twist couplings) are considered in the formulation. Results are extracted based on two methods namely the Eigen-value techniques for frequencies and the Newmark method to calculate the transient response. Then, the obtained results have been verified with the other results available in the literature and very good agreements have been observed. Furthermore, the new results have been obtained for the case where the excitation was due to a moving/non-moving force.

Role of high-order electromechanical coupling terms in thermodynamics of ferroelectric thin films

Currently used methods for the description of thermodynamics of ferroelectric thin films (Landau theory or ab initio based Monte Carlo simulations) are based on an energy expansion in terms of internal degrees of freedom. It was shown that these methods can suffer from a substantial inaccuracy unless higher order electromechanical interactions are taken into account. The high-order electromechanical couplings strongly renormalize the sixth-power polarization terms of the thermodynamic energy expansion. In this paper, apart from the general statement, we illustrate it with an example of a temperature--misfit strain phase diagram of a ${\text{BaTiO}}_{3}$ thin film derived with high-order electromechanical interactions evaluated using first-principles calculations.

Neutron stars with antikaons: Comparison between two ways of extending the relativistic mean field models

Extending the relativistic mean field (RMF) models either with higher order couplings or with density-dependent couplings has been proven to be successful in explaining several properties of finite nuclei, infinite matter, and neutron stars (NSs) in a unified way. Here, we compare how these two extensions fare while explaining NSs with and without antikaons. Both these extensions soften the equation of state (EoS), but the higher order couplings are more efficient in doing so. Even for a very soft EoS, we find that there is a strong possibility of antikaons being condensed. We find an exception for correlation between NS radius and density dependence of symmetry energy, which gets restored when we introduce antikaons. The implication of a precisely measured 2${M}_{\ensuremath{\bigodot}}$ NS on our results is discussed with four sets of interactions which cover all four combinations of stiff and soft symmetry energy and equations of state.

“Pasta phases” in neutron stars studied with extended relativistic mean field models

To explain several properties of finite nuclei, infinite matter, and neutron stars in a unified way within the relativistic mean field models, it is important to extend them either with higher order couplings or with density-dependent couplings. These extensions are known to have strong impact in the high-density regime. Here we explore their role on the equation of state at densities lower than the saturation density of finite nuclei which govern the phase transitions associated with pasta structures in the crust of neutron stars.

Higher-order mode couplings in double-helix chiral long-period fiber gratings

All possible resonant couplings of the core modes with the cladding modes are analyzed comprehensively in double-helix chiral long-period fiber gratings (CLPGs). Couplings with higher order cladding modes that were neglected in previous works are emphasized in this paper, and thus interesting properties are revealed. Two kinds of double-helix CLPGs whose cross-section asymmetry originates from small geometric deformation and stress-induced birefringence, respectively, are analyzed in detail. The similarities and differences of mode selection and polarization selectivity of mode couplings are identified for the two structures.

Approximate scheme by the coupled-wave theory to efficiently analyze the influences of moiré phenomena in liquid-crystal devices

This work studies an approximate scheme by coupled-wave theory to analyze quickly the large-scale moiré phenomena as seen in common liquid-crystal devices. The moiré phenomena are considered to be caused by two periodic structures (with lattice vectors γ[combininb arrow](1) and γ[combininb arrow](2) and show an interference pattern spanning over a length γ(m)=|γ[combininb arrow](1)|·|γ[combininb arrow](2)|/|γ[combininb arrow](1)-γ[combininb arrow](2)| (with γ[combininb arrow](1)=/~γ[combininb arrow](2)). With the coupled-wave theory, the complete analysis of the moiré optics includes at least 2γ(m)/λ (λ: wavelength in vacuum) Fourier components and presents an ineffective computation. This work applies a cos(τ) type approximation for the openings of unpatterned liquid-crystal pixels, and considers the first-order coupling between the Fourier components of pixels and other (periodic) optical structures. We hence arrive at an effective evaluation, including 4τ|γ[combininb arrow](1)|/λ (or 4τ|γ[combininb arrow](2)|/λ) Fourier components, and are able to go back to a complete analysis when considering higher-order couplings at an appropriate τ integer value.

Massive Modes in Magnetized Brane Models

We study higher dimensional models with magnetic fluxes, which can be derived from superstring theory. We study mass spectrum and wavefunctions of massless and massive modes for spinor, scalar and vector fields. We compute the 3-point couplings and higher order couplings among massless modes and massive modes in 4D low-energy effective field theory. These couplings have non-trivial behaviors, because wavefunctions of massless and massive modes are non-trivial.

Efficient calculation of molecular configurational entropies using an information theoretic approximation.

Accurate computation of free energy changes upon molecular binding remains a challenging problem, and changes in configurational entropy are especially difficult due to the potentially large numbers of local minima, anharmonicity, and high-order coupling among degrees of freedom. Here we propose a new method to compute molecular entropies based on the maximum information spanning tree (MIST) approximation that we have previously developed. Estimates of high-order couplings using only low-order terms provide excellent convergence properties, and the theory is also guaranteed to bound the entropy. The theory is presented together with applications to the calculation of the entropies of a variety of small molecules and the binding entropy change for a series of HIV protease inhibitors. The MIST framework developed here is demonstrated to compare favorably with results computed using the related mutual information expansion (MIE) approach, and an analysis of similarities between the methods is presented.

Erratum: Role of higher order couplings in the presence of kaons in relativistic mean field description of neutron stars [Phys. Rev. C85, 015804 (2012)

Erratum: Role of higher order couplings in the presence of kaons in relativistic mean field description of neutron stars [Phys. Rev. C85, 015804 (2012)

Coherent destruction of tunneling in a lattice array under selective in-phase modulations

We explore the coherent destruction of tunneling (CDT) in a lattice array under selective in-phase harmonic modulations, in which some selected lattice sites are driven by in-phase harmonic oscillating fields and other lattice sites are undriven. Due to the occurrence of CDT, if the driving amplitude $A$ and the driving frequency $\omega$ are tuned to satisfy the zeroth-order Bessel function $J_0(A/\omega)=0$, the driven lattice sites are approximately decoupled with the undriven lattice sites. The CDT even takes place in lattice systems with high-order couplings between non-nearest lattice sites. By using the CDT, we propose a scheme for realizing directed transport of a single particle. It is possible to observe the CDT in the engineered optical waveguide array, which provides a new opportunity for controlling light propagation and designing switch-like couplers.

Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3

Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO${}_{3}$ single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability ${\ensuremath{\mu}}_{a}$ [H$\phantom{\rule{0.16em}{0ex}}(\ensuremath{\omega})$ oriented within the hexagonal plane] below the N\'eel temperature ${T}_{N}$. This excitation softens from 41 to 32 $\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ upon heating and finally disappears above ${T}_{N}$. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity ${\ensuremath{\varepsilon}}_{c}$ within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases upon heating toward room temperature, thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 $\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ in the paramagnetic phase in both ${\ensuremath{\varepsilon}}_{c}$ and ${\ensuremath{\varepsilon}}_{a}$ spectra, and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons, however their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon-paramagnon differential absorption processes. The latter is enabled by strong short-range in-plane spin correlations in the paramagnetic phase.

Natural four-generation mass textures in MSSM brane worlds

A fourth generation of standard model fermions is usually considered unlikely due to constraints from direct searches, electroweak precision measurements, and perturbative unitarity. We show that fermion mass textures consistent with all constraints may be obtained naturally in a model with four generations constructed from intersecting $D6$-branes on a ${T}^{6}/({\mathbb{Z}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathbb{Z}}_{2})$ orientifold. The Yukawa matrices of the model are rank 2, so that only the third- and fourth-generation fermions obtain masses at the trilinear level. The first two generations obtain masses via higher-order couplings and are therefore naturally lighter. In addition, we find that the third and fourth generations automatically split in mass, but do not mix at leading order. Furthermore, the standard model gauge couplings automatically unify at the string scale, and all the hidden-sector gauge groups become confining in the range ${10}^{13}--{10}^{16}\text{ }\text{ }\mathrm{GeV}$, so that the model becomes effectively a four-generation minimal supersymmetric standard model at low energies.

Role of the tensor exchange potential in nucleon-nucleus scattering

We give a microscopic derivation of the spin-spin components of the optical potential for elastic scattering of a nucleon from a target with nonzero spin. A realistic nucleon-nucleon interaction containing direct and exchange terms is used to generate a folded nucleon-nucleus potential whose spin-spin components are treated in distorted-wave Born approximation. We show how folding leads to spin-spin tensor interactions with higher order couplings in the projectile and target spin that have not been explicitly considered before. We place particular emphasis on the polarization transfer coefficient DNN for 200-MeV protons elastically scattered from 10 B, which is rigorously unity in the absence of any spin-spin interactions and for which experimental data exist. We find that deviations of DNN from unity are particularly sensitive to spin-spin exchange terms arising from the nucleon-nucleon tensor interaction and the nuclear wave functions describing the target one-body density matrix. Unpolarized differential cross sections and vector analyzing powers are found to be very insensitive to these terms. DOI: 10.1103/PhysRevC.84.041601

MAXIMAL SUPERSYMMETRY AND EXCEPTIONAL GROUPS

The article is a tribute to my old mentor, collaborator and friend Murray Gell-Mann. In it I describe work by P. Ramond, S.-S. Kim and myself where we describe the [Formula: see text] supergravity in the light-cone formalism. We show how the Cremmer–Julia E7(7) nonlinear symmetry is implemented and how the full supermultiplet is a representation of the E7(7) symmetry. I also show how the E7(7) symmetry is a key to understand the higher order couplings in the theory and is very useful when we discuss possible counterterms for this theory.

Detection of Native-State Nonadditivity in Double Mutant Cycles via Hydrogen Exchange

Proteins have evolved to exploit long-range structural and dynamic effects as a means of regulating function. Understanding communication between sites in proteins is therefore vital to our comprehension of such phenomena as allostery, catalysis, and ligand binding/ejection. Double mutant cycle analysis has long been used to determine the existence of communication between pairs of sites, proximal or distal, in proteins. Typically, nonadditivity (or "thermodynamic coupling") is measured from global transitions in concert with a single probe. Here, we have applied the atomic resolution of NMR in tandem with native-state hydrogen exchange (HX) to probe the structure/energy landscape for information transduction between a large number of distal sites in a protein. Considering the event of amide proton exchange as an energetically quantifiable structural perturbation, m n-dimensional cycles can be constructed from mutation of n-1 residues, where m is the number of residues for which HX data is available. Thus, efficient mapping of a large number of couplings is made possible. We have applied this technique to one additive and two nonadditive double mutant cycles in a model system, eglin c. We find heterogeneity of HX-monitored couplings for each cycle, yet averaging results in strong agreement with traditionally measured values. Furthermore, long-range couplings observed at locally exchanging residues indicate that the basis for communication can occur within the native state ensemble, a conclusion not apparent from traditional measurements. We propose that higher-order couplings can be obtained and show that such couplings provide a mechanistic basis for understanding lower-order couplings via "spheres of perturbation". The method is presented as an additional tool for identifying a large number of couplings with greater coverage of the protein of interest.

New modes for subsurface atomic force microscopy through nanomechanical coupling

Non-destructive, nanoscale characterization techniques are needed to understand both synthetic and biological materials. The atomic force microscope uses a force-sensing cantilever with a sharp tip to measure the topography and other properties of surfaces. As the tip is scanned over the surface it experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample. Here we show that an atomic force microscope can obtain a range of surface and subsurface information by making use of the nonlinear nanomechanical coupling between the probe and the sample. This technique, which is called mode-synthesizing atomic force microscopy, relies on multi-harmonic forcing of the sample and the probe. A rich spectrum of first- and higher-order couplings is discovered, providing a multitude of new operational modes for force microscopy, and the capabilities of the technique are demonstrated by examining nanofabricated samples and plant cells.

Levodopa influences the regularity of the ankle joint kinematics in individuals with Parkinson’s disease

The aim of the investigation was to explore the influence of levodopa therapy on the regularity of the structural variations present in the lower extremity joints of individuals with Parkinson's disease (PD). Ten participants with PD walked on a treadmill during the states of "off" and "on" levodopa. Approximate entropy was used to quantify the regularity of the structural variations present in the joint kinematics. Additionally, a pseudo-periodic surrogation analysis was used to evaluate if changes in the regularity of the joint's movement were associated with a noisy or deterministic motor process. This investigation provided two key findings. The first was that the structural variations present in ankle joint were more regular with levodopa therapy. The second was that changes in the structural variations were related to a deterministic motor process. This indicated that the variations present in the walking patterns of individuals with PD most likely arose from higher-order neural couplings rather than noise in the motor process. Monitoring the regularity of the structural variations present in gait may help improve the management of PD.

Higher order couplings in magnetized brane models

We compute three-point and higher order couplings in magnetized brane models. We show that higher order couplings are written as products of three-point couplings. This behavior is the same as higher order amplitudes by conformal field theory calculations e.g. in intersecting D-brane models.