Field Theory Calculations Research Articles

Plausible presence of new state in neutron stars with masses above [formula omitted

We investigate the neutron star (NS) equation of state (EOS) by incorporating multi-messenger data of GW170817, PSR J0030 + 0451, PSR J0740 + 6620, and state-of-the-art theoretical progresses, including the information from chiral effective field theory (χEFT) and perturbative quantum chromodynamics (pQCD) calculation. Taking advantage of the various structures sampling by a single-layer feed-forward neural network model embedded in the Bayesian nonparametric inference, the structure of NS matter’s sound speed cs is explored in a model-agnostic way. It is found that a peak structure is common in the cs2 posterior, locating at (2.4-4.8)ρsat (nuclear saturation density) and cs2 exceeds c2/3 at 90% credibility. The non-monotonic behavior suggests evidence of the state deviating from the hadronic matter inside the very massive NSs. Assuming the new/exotic state is featured as it is softer than typical hadronic models or even with hyperons, we find that a sizable (⩾10-3M⊙) exotic core, likely made of quark matter, is plausible for the NS with a gravitational mass above about 0.98MTOV, where MTOV represents the maximum gravitational mass of a non-rotating cold NS. The inferred MTOV=(2.18-0.13+0.27)M⊙ (90% credibility) is well consistent with the value of (2.17-0.12+0.15)M⊙ estimated independently with GW170817/GRB 170817A/AT2017gfo assuming a temporary supramassive NS remnant formed after the merger. PSR J0740 + 6620, the most massive NS detected so far, may host a sizable exotic core with a probability of ≈0.36.

Large-time correlation functions in bosonic lattice field theories

Large-time correlation functions have a pivotal role in extracting particle masses from Euclidean lattice field theory calculations, however little is known about the statistical properties of these quantities. In this work, the asymptotic form of the distributions of the correlation functions at vanishing momentum is determined for bosonic interacting lattice field theories with a unique gapped vacuum. It is demonstrated that the deviations from the asymptotic form at large Euclidean times can be utilized to determine the spectrum of the theory.

Strategies for quantum-optimized construction of interpolating operators in classical simulations of lattice quantum field theories

It has recently been argued that noisy intermediate-scale quantum computers may be used to optimize interpolating operator constructions for lattice quantum field theory (LQFT) calculations on classical computers. Here, two concrete realizations of the method are developed and implemented. The first approach is to maximize the overlap, or fidelity, of the state created by an interpolating operator acting on the vacuum state to the target eigenstate. The second is to instead minimize the energy expectation value of the interpolated state. These approaches are implemented in a proof-of-concept calculation in ($1+1$)-dimensions for a single-flavor massive Schwinger model to obtain quantum-optimized interpolating operator constructions for a vector meson state in the theory. Although fidelity maximization is preferable in the absence of noise due to quantum gate errors, it is found that energy minimization is more robust to these effects in the proof-of-concept calculation. This work serves as a concrete demonstration of how quantum computers in the intermediate term might be used to accelerate classical LQFT calculations.

Alternating Gyroid Stabilized by Surfactant-like Triblock Terpolymers in IS/SO/ISO Ternary Blends

Block polymers self-assembled into chiral alternating-gyroid (GA) morphologies are desirable templates for fabricating photonic materials. Recent self-consistent field theory (SCFT) calculations on a model system predicted that adding a minuscule amount of ABC triblocks into a blend of thermodynamically symmetric double-gyroid-forming AB and BC diblocks with immiscible A and C blocks stabilizes GA. Here, we use SCFT to investigate the feasibility of this method in practice by computing the phase behaviors of ternary mixtures of poly(isoprene-b-styrene) (IS), poly(styrene-b-ethylene oxide) (SO), and poly(isoprene-b-styrene-b-ethylene oxide) (ISO). Addition of ISO indeed stabilizes GA; however, the phase window is relatively narrow, due to the packing frustration induced by the mismatch in preferred domain sizes between IS and SO diblock copolymers. Designing the system to have comparable diblock domain sizes significantly enhances the relative stability of GA against the competing alternating lamellae, and this stability is also sensitive to the degree of polymerization of the ISO midblock. Moreover, the stabilization of alternating morphologies is sensitive to temperature, and less ISO is needed at lower temperatures. The effect of some other design parameters, such as diblock volume fraction, is also investigated. These computational results provide insights into possible experimental strategies for producing GA and highlight the sensitivity of network phase formation to asymmetries in the thermodynamic parameters.

Neural-network preconditioners for solving the Dirac equation in lattice gauge theory

This work develops neural-network--based preconditioners to accelerate solution of the Wilson-Dirac normal equation in lattice quantum field theories. The approach is implemented for the two-flavor lattice Schwinger model near the critical point. In this system, neural-network preconditioners are found to accelerate the convergence of the conjugate gradient solver compared with the solution of unpreconditioned systems or those preconditioned with conventional approaches based on even-odd or incomplete Cholesky decompositions, as measured by reductions in the number of iterations and/or complex operations required for convergence. It is also shown that a preconditioner trained on ensembles with small lattice volumes can be used to construct preconditioners for ensembles with many times larger lattice volumes, with minimal degradation of performance. This volume-transferring technique amortizes the training cost and presents a pathway towards scaling such preconditioners to lattice field theory calculations with larger lattice volumes and in four dimensions.

Evanescent operators in one-loop matching computations

Effective Field Theory calculations used in countless phenomenological analyses employ dimensional regularization, and at intermediate stages of computations, the operator bases extend beyond the four-dimensional ones. The extra pieces — the evanescent operators — can ultimately be removed with a suitable renormalization scheme, resulting in a finite shift of the physical operators. Modern Effective Field Theory matching techniques relying on the method of expansion by regions have to be extended to account for this. After illustrating the importance of these shifts in two specific examples, we compute the finite shifts required to remove all evanescent operators appearing in the one-loop matching of generic ultraviolet theories to the Standard Model Effective Field Theory and elucidate the formalism for generic Effective Field Theory calculations.

Modern multiloop calculations

Loop integrals and methods of their evaluations are vital for perturbative calculations in any quantum field theory. As the order of perturbation theory increases the complexity of the relevant multiloop integrals explodes rapidly. In the present contribution I review methods of modern multiloop calculations with the emphasis on the method based on the IBP reduction and differential equations.

Patterning of Polymer-Functionalized Nanoparticles with Varied Surface Mobilities of Polymers.

The polymers can be either dynamically tethered to or permanently grafted to the nanoparticle to produce polymer-functionalized nanoparticles. The surface mobility of polymer ligands with one end anchored to the nanoparticle can affect the surface pattern, but the effect remains unclear. Here, we addressed the influence of lateral polymer mobility on surface patterns by performing self-consistent field theory calculations on a modeled polymer-functionalized nanoparticle consisting of immobile and mobile brushes. The results show that except for the radius of nanoparticles and grafting density, the fraction of mobile brushes substantially influences the surface patterning of polymer-functionalized nanoparticles, including striped patterns and patchy patterns with various patches. The number of patches on a nanoparticle increases as the fraction of mobile brushes decreases, favored by the entropy of immobile brushes. Critically, we found that broken symmetry usually occurs in patchy nanoparticles, associated with the balance of enthalpic and entropic effects. The present work provides a fundamental understanding of the dependence of surface patterning on lateral polymer mobility. The work could also guide the preparation of diversified nanopatterns, especially for the asymmetric patchy nanoparticles, enabling the fundamental investigation of the interaction between polymer-functionalized nanoparticles.

Opus on conformal symmetry of the Nambu–Goto versus Polyakov strings

I investigate the Nambu–Goto and Polyakov strings, accounting for higher-derivative terms in the emergent action for the metric tensor which are classically negligible for smooth metrics but revive quantumly. Using the conformal field theory technique by KPZ-DDK, I compute in the one-loop approximation the conformal dimension and the central charge which differs in the two cases, telling the Nambu–Goto and Polyakov strings apart. I confirm the results by explicit quantum field theory computations of the propagator and the energy–momentum tensor at one loop, using the Pauli–Villars regularization.

Evidence of electron correlation and weak bulk plasmon in SrMoO3

We investigate the electronic structure of highly conducting perovskite SrMoO3 using valence band photoemission spectroscopy and electronic structure calculations. Large intensity corresponding to coherent feature close to Fermi level is captured by density functional theory (DFT) calculation. An additional satellite at ∼3 eV binding energy remains absent in DFT, hybrid functional (DFT-hybrid) and dynamical mean field theory (DFT + DMFT) calculations. Mo 4d spectra obtained with different surface sensitive photoemission spectroscopy suggest different surface and bulk electronic structures. DFT + DMFT spectral function is in excellent agreement with the coherent feature in the bulk Mo 4d spectra, revealing moderate electron correlation strength. A large plasmon satellite and signature of strong electron correlation are observed in the surface spectra, while the bulk spectra exhibits a weak plasmon satellite.

Nanolaminated Fe2AB2 and Mn2AB2 (A = Al,Si,Ga,In) materials and the assessment of their electronic correlations

Ternary transition metal carbides and nitrides in the so-called MAX phases constitute a rich family of compounds that host interesting electronic and magnetic properties, and thus, these materials have been drawing increasing levels of attention. Similar ternary boride compounds, the MAB phases, have been studied much less despite being equally if not more promising. In this paper, we investigate ${\mathrm{Fe}}_{2}A{\text{B}}_{2}$ and ${\mathrm{Mn}}_{2}A{\text{B}}_{2} (A=\mathrm{Al},\mathrm{Si},\mathrm{Ga},\phantom{\rule{0.28em}{0ex}}\text{and}\phantom{\rule{0.28em}{0ex}}\mathrm{In})$ ternary layered transition metal borides with orthorhombic, hexagonal, and tetragonal crystal structures using first-principles density functional theory (DFT). We assess the reliability of different exchange-correlation functionals for the accurate prediction of the material properties of MAB phases. In addition to the electronic and crystal structures of ${\mathrm{Fe}}_{2}A{\text{B}}_{2}$ and ${\mathrm{Mn}}_{2}A{\text{B}}_{2}$ ($A$ = Ga, In, and Si), we predict the dynamical and thermodynamic stabilities against the competing phases. We conducted bonding analysis to comprehend the bonding characteristic between different atoms, which provides a fundamental understanding whether the exfoliation of these compounds into so-called two-dimensional MBene structures is likely or not. In addition to spin-polarized $\mathrm{DFT}+U$ calculations, which predict ordered magnetic moments, our $\mathrm{DFT}+$embedded dynamical mean field theory calculations predict a significant degree of electronic correlations in the paramagnetic phase of these compounds. These calculations also predict the formation of fluctuating magnetic moments before the onset of a magnetic order in the MAB compounds like an earlier report on the MAX compound ${\mathrm{Mn}}_{2}\mathrm{GaC}$.

Understanding the systematic differences in extractions of the proton electric form factors at low Q2

Systematic differences exist between values of the proton's electric form factors in the low-$Q^2$ region extracted by different experimental and theoretical groups, though they are all making use of basically the same electron-proton scattering data. To try understand the source of these differences, we make use of the analytically well-behaved rational (N=1, M=1) function, a predictive function that can be reasonably used for extrapolations at $Q^{2} \rightarrow 0$. First, we test how well this deceptively simple two-parameter function describes the extremely complex and state-of-the-art dispersively improved chiral effective field theory calculations. Second, we carry out a complete re-analysis of the 34 sets of eletron-proton elastic scattering cross-section data of the Mainz A1 Collaboration with its unconstrained 31 normalization parameters up to $Q^{2} = 0.5~{\rm (GeV/c)^{2}}$. We find that subtle shifts in the normalization parameters can result in relatively large changes in the extracted physical qualities. In conclusion, we show that by simply using a well-behaved analytic function, the apparent discrepancy between recent form-factor extractions can be resolved.

Orientation control of the hexagonal and lamellar phases in thin block copolymer films using in-plane AC electric field

Lamellar and hexagonal pattern rearrangements in thin films of polystyrene–block–poly(2-vinyl pyridine) and polystyrene–block–poly(4-vinyl pyridine) copolymers simultaneously exposed to an in-plane AC electric field and saturated chloroform vapor are studied with atomic force microscopy and analyzed via the numerical solution of the self-consistent field theory equations. It is demonstrated that the use of AC field with the root-mean-square strength higher than 8 V⋅μm−1 allows one to effectively orient microphase-separated domains along the field direction on the tens of microns scale. At the same time, the AC field considerably lowers the risk of breakdown and eliminates effects related to ionic transport in the presence of solvent vapor. The role of such factors as the exposure time, field strength and frequency is investigated. Theoretical considerations prove the equivalent effect of AC and DC fields on the structure of the copolymer film in a wide frequency range. Self-consistent field theory calculations of the free energy as a function of film thickness make it possible to exactly identify which phase dominates in the film. In particular, an apparent transformation of standing cylinders into long threads aligned in the field direction should be interpreted as the phase transition from the perpendicular to parallel hexagonal phase, which can take place in a certain range of film thicknesses, provided the electric field strength exceeds a certain threshold value. In the case of a perpendicular lamellar phase, the domain orientation along the direction of the electric field is always profitable. The observed morphological rearrangements under an in-plane field, which preserve connectivity between the film surfaces through the domains of the minor copolymer block, can be important for practical applications.

The exact renormalization group and dimensional regularization

The exact renormalization group (ERG) is formulated implementing the decimation of degrees of freedom by means of a particular momentum integration measure. The definition of this measure involves a distribution that links this decimation process with the dimensional regularization technique employed in field theory calculations. Taking the dimension [Formula: see text], the one-loop solutions to the ERG equations for the scalar field theory in this scheme are shown to coincide with the dimensionally regularized perturbative field theory calculation in the limit [Formula: see text], if a particular relation between the scale parameter [Formula: see text] and [Formula: see text] is employed. In general, it is shown that in this scheme the solutions to the ERG equations for the proper functions coincide when [Formula: see text] with the complete diagrammatic contributions appearing in field theory for these functions and this theory, provided that exact relations between [Formula: see text] and [Formula: see text] hold. In addition, a nonperturbative approximation is considered. This approximation consists in a truncation of the ERG equations, which by means of a low-momentum expansion leads to reasonable results.

Pressure-driven change of ground state of Ce3Pd3Bi4 : A DFT+DMFT study

A candidate material for strongly correlated topological materials, ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ has attracted much attention, but its ground state remains controversial. Compared with the typical Kondo insulator ${\mathrm{Ce}}_{3}{\mathrm{Pt}}_{3}{\mathrm{Bi}}_{4}$, two possibilities of ground states are proposed: ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ is either a spin--orbit-driven topological semimetal or a Kondo insulator with less Kondo coupling strength than platinum. Here, we performed density functional theory $(\mathrm{DFT})+\mathrm{dynamical}$ mean field theory (DMFT) calculations on ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ under different pressures to clarify its ground state, as pressure can tune the strength of Kondo coupling without affecting the strength of spin-orbit coupling. We found ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ has a metallic ground state and becomes insulating with increasing pressure at a low temperature. And as the pressure increased to 2 GPa, a hybridization energy gap can be observed at 10 K. As the pressure increased to 5 GPa, the electronic structure of ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ is even similar to that of the Kondo insulator ${\mathrm{Ce}}_{3}{\mathrm{Pt}}_{3}{\mathrm{Bi}}_{4}$ under ambient pressure, and a clear hybridization energy gap $(\ensuremath{\sim}3\phantom{\rule{0.28em}{0ex}}\mathrm{meV})$ appears at 20 K. Our results not only demonstrate that the key factor controlling the different ground states between the two compounds is Kondo physics, rather than spin-orbit coupling, but also confirm that ${\mathrm{Ce}}_{3}{\mathrm{Pd}}_{3}{\mathrm{Bi}}_{4}$ is an ideal material to tuning the ground states by changing the strength of hybridization by pressure.

Gauge-equivariant flow models for sampling in lattice field theories with pseudofermions

This work presents gauge-equivariant architectures for flow-based sampling in fermionic lattice field theories using pseudofermions as stochastic estimators for the fermionic determinant. This is the default approach in state-of-the-art lattice field theory calculations, making this development critical to the practical application of flow models to theories such as QCD. Methods by which flow-based sampling approaches can be improved via standard techniques such as even/odd preconditioning and the Hasenbusch factorization are also outlined. Numerical demonstrations in two-dimensional U(1) and SU(3) gauge theories with ${N}_{f}=2$ flavors of fermions are provided.

In Situ Electrothermal Approach for the Synthesis of High-Performance Carbon Fiber

Carbon fibers (CFs) have long been of great interest as a crucial material for the aerospace industry. Their practical application requires higher performance and efficient fabrication. This study presents an in situ electrothermal approach for graphitizing CFs. During the electrothermal process, an electric field manipulates the growth of graphite microcrystalline structures, yielding single, regular, large graphite microcrystals, thereby inducing their alignment. The in situ electrothermal approach increased the strength of the resulting CFs by 50.3% and enhanced their Young’s moduli by 9.2% compared with conventional approaches. Moreover, the use of a molecular dynamics (MD)–Reaxff force field and density functional theory calculations in conjunction with the characterization tools revealed the positive effect of the electric field on microcrystalline growth, which explains the peculiar microstructures and enhanced mechanical properties of CFs prepared using the electrothermal approach. Accordingly, this approach is expected to be a better alternative to the current graphitization and carbonization process in the future.

Nucleus size and its effect on nucleosome stability in living cells

DNA architectural proteins play a major role in organization of chromosomal DNA in living cells by packaging it into chromatin, whose spatial conformation is determined by an intricate interplay between the DNA-binding properties of architectural proteins and physical constraints applied to the DNA by a tight nuclear space. Yet, the exact effects of the nucleus size on DNA-protein interactions and chromatin structure currently remain obscure. Furthermore, there is even no clear understanding of molecular mechanisms responsible for the nucleus size regulation in living cells. To find answers to these questions, we developed a general theoretical framework based on a combination of polymer field theory and transfer-matrix calculations, which showed that the nucleus size is mainly determined by the difference between the surface tensions of the nuclear envelope and the endoplasmic reticulum membrane as well as the osmotic pressure exerted by cytosolic macromolecules on the nucleus. In addition, the model demonstrated that the cell nucleus functions as a piezoelectric element, changing its electrostatic potential in a size-dependent manner. This effect has been found to have a profound impact on stability of nucleosomes, revealing a previously unknown link between the nucleus size and chromatin structure. Overall, our study provides new insights into the molecular mechanisms responsible for regulation of the nucleus size, as well as the potential role of nuclear organization in shaping the cell response to environmental cues.

Tapir: A tool for topologies, amplitudes, partial fraction decomposition and input for reductions

The demand for precision predictions in the field of high energy physics has dramatically increased over recent years. Experiments conducted at the LHC, as well as precision measurements at the intensity frontier such as Belle II require equally precise theoretical predictions to make full use of the acquired data. To match the experimental precision, second-, third- and, for certain quantities, even higher-order calculations in perturbative quantum field theory are required.To facilitate such calculations, computer software automating as many steps as possible is required. Yet, each calculation poses different challenges and thus, a high level of configurability is required. In this context we present tapir: a tool for identification, manipulation and minimization of Feynman integral families. It is designed to integrate in toolchains based on the computer algebra system FORM, the use of which is common practice in the field. tapir can be used to reduce the complexity of multi-loop problems with cut-filters, topology mapping, partial fraction decomposition and alike. Program summaryProgram Title:tapirCPC Library link to program files:https://doi.org/10.17632/ptc9t46xyn.1Developer's repository link:https://gitlab.com/tapir-devs/tapirLicensing provisions: GPLv3Programming language:python 3, C++Nature of problem: Multi-loop computations require the automatization of a large number of different tasks related to Feynman integral topologies. Among them are the identification and minimization of integral topologies, partial fraction decomposition of topologies in the case of linearly dependent propagators as well as mapping scalar products of loop momenta to scalar functions.Solution method: The minimization of topologies is performed by comparison of their respective Nickel indices [1], even further minimization utilizes Pak's algorithm [2]. To efficiently map scalar products of loop momenta to scalar functions FORM [3] code is generated.Additional comments including restrictions and unusual features: Minimization based on Pak's algorithm slows down for many lines and scales. A coarser minimization using the Nickel indices, however, is still possible.

Computational Challenges for Multi-loop Collider Phenomenology

Precision measurements at the LHC and future colliders require theory predictions with uncertainties at the percent level for many observables. Theory uncertainties due to the perturbative truncation are particularly relevant and must be reduced to fully exploit the physics potential of collider experiments. In recent years the theoretical high energy physics community has made tremendous analytical and numerical advances to address this challenge. In this white paper, we survey state-of-the-art calculations in perturbative quantum field theory for collider phenomenology with a particular focus on the computational requirements at high perturbative orders. We show that these calculations can have specific high-performance-computing (HPC) profiles that should to be taken into account in future HPC resource planning.