Off-shell Research Articles

The evolution of the coronal loop structure due to the phase mixing of high and low-frequency Alfvén waves

ABSTRACT Coronal loops are known to host Alfvén waves propagating in the corona from the lower layers of the solar atmosphere and because of their internal structure, phase mixing is likely to occur. The structure of the coronal loop could be significantly affected by the thermodynamic feedback of the heating generated by phase mixing. However, this phenomenon can be sensitive to the period of the propagating Alfvén waves due to how short period waves can be easily dissipated and the way long-period waves may accumulate considerable energy in resonating coronal loops. Using the Lare2d code, a coronal loop model of a field-aligned thermodynamic equilibrium and a cross-field background heating profile is created, with an additional forcing term added to drive Alfvén waves with coronal amplitudes between $5{\!-\!}30 \, \mathrm{km} \, \mathrm{s}^{-1}$. We show that high-frequency waves can generate heating corresponding to a ${\sim} 10~{{\ \rm per\ cent}}$ increase of the initial coronal shell temperature, chromospheric upflows of up to $0.6 \, \mathrm{km} \, \mathrm{s}^{-1}$ and a coronal shell mass increase of ${\sim} 15~{{\ \rm per\ cent}}$. These changes are sufficient to alter and maintain a new coronal loop density structure, broadening the region where efficient phase mixing (and therefore heating) occurs. In contrast, low-frequency waves are unable to be effectively dissipated, resulting in minimal changes to the loop structure. We see little evidence of wave energy accumulation in the corona and are unable to conclude that the dissipation of low-frequency Alfvén waves can be an effective heating mechanism in coronal loops in the setup used in this study.

Convective vortices in collapsing stars

Abstract Recent studies show that non-radial structures arising from massive star shell convection play an important role in shaping core-collapse supernova explosions. During the collapse phase, convective vortices generate acoustic waves that interact with the supernova shock. This amplifies turbulence in the post-shock region, contributing to explosion. We study how various physical parameters influence the evolution of these convective vortices during stellar collapse using simplified simulations. We model the collapsing star with a transonic Bondi flow and represent convection as solenoidal velocity perturbations. Our results are consistent with previous studies, demonstrating that the peak perturbation amplitude scales linearly with the pre-collapse convective Mach number and inversely with the angular wavenumber of convection. While the shell radius and width primarily determine the timescale of accretion, they have little impact on the peak perturbation amplitudes. Finally, we show that when the convective Mach number is below approximately 0.2, the dynamics remain within the linear regime.

Modification of Chitosan Isolation Method from Pearl Oyster Shell (Pinctada maxima sp) as A Source of Natural Polymer

Abstract Chitosan is natural polymer with abundant availability and unique characteristics. The purpose of this study was to investigate the effects of various isolation methods on chitosan properties. Chitosan was obtained by isolation method using oyster pearl shell (Pinctada maxima sp.). The parameters of the deacetylation process are the comparison of heating method with microwave method and the comparison of microwave power. Chitosan was characterized for degree of deacetylation (DD) and functional groups by FTIR, and viscosity by Brookfield viscometer. The microwave method was faster than the heating method. Then, the larger mass of shell and %NaOH produced a higher DD of 89.75%. However, the use of 60g mass and 60% NaOH resulted in an already high DD of 81.96%. Furthermore, variation microwave power showed the highest DD at high power. FTIR spectrum analysis showed the appearance of chitosan functional groups, OH and NH2 groups. The viscosity value decreased as the microwave power increased. Based on this study, different isolation methods affect the quality of chitosan. However, it’s necessary to conduct more detailed research related to changes in chemical structure. Therefore, oyster shells can produce chitosan as a source of natural polymers with different characteristics.

Light scalar quarkonia from Laplace sum rule at NLO

We review our results on light scalar quarkonia (q¯q and four-quark states) from (inverse) QCD Laplace sum rules (LSR) and their ratios R within stability criteria and including higher order perturbative (PT) corrections up to the (estimated) O(αs5). As the Operator Product Expansion (OPE) usually converges for D⩽6−8, we evaluated the QCD spectral functions at Lowest Order (LO) of PT QCD and up to the D=6 dimension vaccum condensates. We request that the optimal results obey the constraint: Pole (Resonance) contribution to the spectral integral is larger than the QCD continuum one which excludes an on-shell mass around (500−600)MeV obtained for values of the QCD continuum threshold tc⩽(1∼1.5)GeV2. Our results for the different assignments of the scalar mesons are compiled in Tables 1 to 3.

Analytic bounds on late-time axion-scalar cosmologies

The cosmological dynamics of multiple scalar/pseudoscalar fields are difficult to solve, especially when the field-space metric is curved. This presents a challenge in determining whether a given model can support cosmic acceleration, without solving for the on-shell solution. In this work, we present bounds on late-time FLRW-cosmologies in classes of theories that involve arbitrary numbers of scalar and pseudoscalar fields coupled both kinetically (leading to a curved field space metric) and through scalar potentials. Such bounds are proven analytically, independently of initial conditions, with no approximation in the field equations and without referring to explicit solutions. Besides their broad applications to cosmological model building, our bounds can be applied to studying asymptotic cosmologies of certain classes of string compactifications.

Precise determination of the bottom-quark on-shell mass using its four-loop relation to the $\overline{\rm MS}$-scheme running mass

Precise determination of the bottom-quark on-shell mass using its four-loop relation to the $\overline{\rm MS}$-scheme running mass

A study on the synthesis of superheavy element Mc (Z = 115) using lead, bismuth and actinide targets

The evaporation residue cross sections in synthesizing isotopes of superheavy element Mc (Z = 115) by the hot fusion reactions 48Ca+241,243Am→289,291Mc, 45Sc+240,242,244Pu→285,287,289Mc, 50Ti+236,237Np→286,287Mc, 51V+238U→289Mc, 36S+253Es→289Mc, 46K+248Cm→294Mc, and by the cold fusion reactions 78As+208Pb→286Mc, 76Ge+209Bi→285Mc have been systematically investigated using the phenomenological model for production cross section. We have predicted the most effective projectile-target combinations for synthesizing Mc isotopes among these reactions. Our result shows that the 3n- channel cross section is larger for the reaction 48Ca+243Am→291Mc, and the 4n- channel cross section is larger for the reaction 46K+248Cm→294Mc. This study also examines the effect of the use of mass values and shell corrections by the Möller and Warsaw groups. Using our predicted combinations and the cross section values at a range of excitation energies, we hope these isotopes of Mc can be synthesized in near-future experiments.

Changes in the fruits and seeds morphometric, germination, phytochemicals content, and antioxidant capacity in seed ripening of Echinocereus stramineus

Within the cacti family, most studies have focused on the physicochemical characterization of the stems, fruits, and seeds from Mammillaria, Opuntia, Hylocereus, and Stenocereus genera. However, few information is focused on the morphological and physicochemical characterization of the stems, fruits, and seeds of other genera widely distributed in the arid and semiarid zones of the Chihuahuan desert, such as the genus Echinocereus. The objective of this study was to analyze the fruit morphology, morphometry, germination process, and phytochemical content in four stages of seed in fruit ripening from E. stramineus. Morphometric parameters were measured by picking ten fruits and sixty seeds for each ripening stage. The characterization of the germination process included the germination percentage, mean germination time, germination speed, and mean germination speed which were computed 21 days after germination. The quantification of total phenols, flavonoids, tannins, reducing sugars, protein, and antioxidant activity of seeds was determined using colorimetric approaches under basal conditions. The morphometric results revealed a negative correlation between the fruit ripening stage and total mass (r= -0.980, p = 0.020), shell mass (r= -0.986, p = 0.014), pulp mass (r = -0.979, p = 0.021), fruit length (r = -0.978, p = 0.022), fruit width (r = -0.968, p = 0.032) and fruit area (r = -0.960, p = 0.04). The germination characterization process showed a negative association between the fruit ripening stage and the seed germination percentage (r = -0.979, p = 0.021) and between the seed mean germination time and the mean germination speed (r= -0.986, p = 0.014). The content of flavonoids, reducing sugars, proteins, and antioxidant capacity showed significant differences among the four stages of fruit ripening; however, no association was found between seed phytochemical content and the ripening stage. This study provides the first data on seed phytochemicals and information on the germination process of E. stramineus seeds.

A de Sitter S-matrix from amputated cosmological correlators

Extending scattering to states with unphysical mass values (particles “off their mass shell”) has been instrumental in developing modern amplitude technology for Minkowski spacetime. Here, we study the off-shell correlators which underpin the recently proposed S-matrix for scattering on de Sitter spacetime. By labelling each particle with both a spatial momentum and an independent “energy” variable (the de Sitter analogue of a 4-momentum), we find that the practical computation of these correlators is greatly simplified. This allows us to derive compact expressions for all 3- and 4-particle S-matrices at tree-level for scalar fields coupled through any derivative interactions. As on Minkowski, we find that the 3-particle and exchange part of the 4-particle S-matrices are unique (up to crossing). The remaining contact part of the 4-particle S-matrix is an analytic function of just two differential operators, which become the usual Mandelstam variables in the Minkowski limit. Finally, we introduce a spectral decomposition for the tree-level exchange of a heavy field responsible for a cosmological collider signal. Once projected onto physical mass eigenstates, these S-matrix elements encode the statistical properties of the early inflationary perturbations.

Mass fluctuations in non-rotating BTZ black holes

We investigate the impact of oscillations of a black hole's mass around its average value on the three-dimensional black hole geometry. Drawing on a classical framework that conceptualizes fluctuations near an event horizon as mass variations, we introduce a model where the metric of a black hole, formed from the collapse of a massive null shell, exhibits oscillatory behavior in spherical modes. This dynamic is encapsulated by a non-rotating BTZ-Vaidya solution, characterized by the black hole mass fluctuating at a resonant frequency ω and a small amplitude parameter μ0. Using a perturbative approach, solutions to the null geodesic equation are determined up to the second order in μ0. The temporal fluctuations of the event horizon's location induce alterations in the thermodynamic variables' values. Upon calculating the time-averaged values, the mean Hawking temperature experiences a slight decrease due to these fluctuations, while the mean entropy exhibits an increase. Furthermore, the study explores the influence of these fluctuations on the trajectories of null rays near the horizon, which ultimately reach the anti-de Sitter boundary at late times. The analytical computation of the general solution for the perturbed rays up to the second order underscores the novel approach of this study in examining the effects of mass oscillations on black hole thermodynamics and geometry, thereby contributing a unique perspective to the field.

Quantum gravity of the Heisenberg algebra

We consider a simplified model of double scaled SYK (DSSYK) in which the Hamiltonian is the position operator of the Harmonic oscillator. This model captures the high temperature limit of DSSYK but could also be defined as a quantum theory in its own right. We study properties of the emergent geometry including its dynamics in response to inserting matter particles. In particular, we find that the model displays de Sitter-like properties such as that infalling matter reduces the rate of growth of geodesic slices between the two boundaries. The simplicity of the model allows us to compute the full generating functional for correlation functions of the length mode or any number of matter operators. We provide evidence that the effective action of the geodesic length between boundary points is non-local. Furthermore, we use the on-shell solution for the geodesic lengths between any two boundary points to reconstruct an effective bulk metric and reverse engineer the dilaton gravity theory that generates this metric as a solution.

Snail shell shape, force of attachment, and metabolic rate together cope with the intertidal challenge

Inhabitants of rocky intertidal shores, including gastropods, require specific adaptations to cope with numerous challenges that vary across the intertidal levels. We collected Stramonita biserialis snails from upper (wave-protected and intense predation) and lower (wave-exposed and low predation) intertidal sites to compare the following traits: shell skeleton (ventral and abaxial lateral views of shell shape, thickness, and mass), foot size, energy metabolism, and attachment strength to determine whether the trait values of snails from each zone fit the environmental challenges they face. We used a Principal Component Analysis to reduce the dimensionality of the data. Multivariate Analysis of Covariance (MANCOVA) for comparing characteristics between the two intertidal zones, and Partial Least Squares (PLS) analyses for testing the integration of overall snail characteristics. The traits of the snails of the two intertidal sites matched with the adaptations expected to allow them to cope with their contrasting challenges. The snails from the lower intertidal had more streamlined shells (which reduces drag forces) and a larger aperture and foot extension (which increase the strength of their attachment to the substrate) compared to snails from the upper sites. Snails from the lower intertidal also had a high mass-specific metabolism and soft body proportion, indicating that these snails from the wave-exposed sites have an energetically active musculature that matches their strong substrate attachment. The thin shell walls of the snails of the lower intertidal match the relatively low predatory pressure there.

Evolution of Lithium Metal Anode Along Cycling in Working Lithium–Sulfur Batteries

AbstractThe cycling lifespan of high‐energy‐density lithium–sulfur (Li–S) batteries is dominantly limited by the rapid failure of Li metal anodes. Herein, the evolution of Li metal anode along cycling is systematically investigated in Li–S batteries to clarify the Li plating and stripping behaviors, the generation and accumulation of inactive Li, and the failure mechanism of Li metal anodes. Concretely, plated Li strips preferentially than bulk Li to leave massive stripping Li shells during initial discharge, and the stripping Li shells are refilled by plated Li during the subsequent charge to generate thick Li dendrites. During the following cycles, inactive Li generates and accumulates on top of bulk Li due to solid electrolyte interphase formation and incomplete removal of plated Li. Eventually, the accumulation of inactive Li hinders the diffusion of Li ions through the inactive Li layer to induce cell polarization at the end of the second discharge plateau and rapid decay of discharge capacity. This work elucidates the detailed evolution mechanism of Li metal anode along cycling in working Li–S batteries and highlights the reactivation of inactive Li as an effective strategy to prolong the cycling lifespan of Li–S batteries.

Probing the dynamical and kinematical structures of detached shells around AGB stars

Context. The chemical evolution of asymptotic giant branch (AGB) stars is driven by repeated thermal pulses (TPs). The duration of a TP is only a few hundred years, whereas an inter-pulse period lasts 104 − 105 yr. Direct observations of TPs are hence unlikely. However, the detached shells seen in CO line emission that are formed as a result of a TP provide indirect constraints on the changes experienced by the star during the pulse. Aims. We aim to resolve the spatial and kinematic sub-structures in five detached-shell sources to provide detailed constraints for hydrodynamic models that describe the formation and evolution of the shells. Methods. We used observations of the 12CO (1 − 0) emission towards five carbon-AGB stars with ALMA (Atacama Large Millimeter/submillimeter Array), including previously published observations of the carbon AGB star U Ant. The data have angular resolutions of 0″​​.3 to 1″ and a velocity resolution of 0.3 km s−1. This enabled us to quantify spatial and kinematic structures in the shells. Combining the ALMA data with single-dish observations of the 12CO (1 − 0) to 12CO (4 − 3) emission towards the sources, we used radiative transfer models to compare the observed structures with previous estimates of the shell masses and temperatures. Results. The observed emission is separated into two distinct components: a more coherent, bright outer shell and a more filamentary, fainter inner shell. The kinematic information shows that the inner sub-shells move at a higher velocity relative to the outer sub-shells. The observed sub-structures reveal a negative velocity gradient outwards across the detached shells, confirming the predictions from hydrodynamical models. However, the models do not predict a double-shell structure, and the CO emission likely only traces the inner and outer edges of the shell, implying a lack of CO in the middle layers of the detached shell. Previous estimates of the masses and temperatures are consistent with originating mainly from the brighter subshell, but the total shell masses are likely lower limits. Also, additional structures in the form of partial shells outside the detached shell around V644 Sco, arcs within the shell of R Scl, and a partially filled shell for DR Ser indicate a more complicated evolution of the shells and mass-loss process throughout the TP cycle than previously assumed. Conclusions. The observed spatial and kinematical splittings of the shells appear consistent with results from the hydrodynamical models, provided the CO emission does not trace the H2 density distribution in the shell but rather traces the edges of the shells. The hydrodynamical models predict very different density profiles depending on the evolution of the shells and the different physical processes involved in the wind-wind interaction (e.g. heating and cooling processes). It is therefore not possible to constrain the total shell mass based on the CO observations alone. Additional features outside and inside the shells complicate the interpretation of the data. Complementary observations of, for example, CI as a dissociation product of CO would be necessary to understand the distribution of CO compared to H2, in addition to new detailed hydrodynamical models of the pre-pulse, pulse, and post-pulse wind. Only a comprehensive combination of observations and models will allow us to constrain the evolution of the shells and the changes in the star during the thermal-pulse cycle.

Microscopic derivation of the octupole magic numbers from symmetry considerations

The valence shells of medium mass and heavy nuclei consist of the normal and the intruder parity orbitals; therefore the Shell Model SU(3) symmetry of Elliott cannot have a straightforward application on them. The proxy-SU(3) can be applied instead, since it uses a unitary transformation, meant to act on the intruder orbitals to alter their parity and transform them to their proxy orbitals. The inverse unitary operator transforms the proxy orbitals back to the intruder ones. The highest weight proxy-SU(3) irreducible representations (irreps) allows one to determine the corresponding number of occupied intruder orbitals. In this way we obtain the so-called ‘octupole magic numbers’ 32, 56, 90, 134 and 194 without any parameter. Moreover, the proxy (unitary) mapping and its inverse transformation make the proxy space eligible for the calculation of observables associated with octupole deformation and the relevant treatment of mixed parity states. The implemented study validates the proxy-SU(3) approach with respect to the octupole deformation and suggests its full applicability in the corresponding mass regions.

How much strangeness is needed for the axial-vector form factor of the nucleon?

We consider the axial-vector together with its induced pseudoscalar form factor of the nucleon as computed from the chiral Lagrangian with nucleon and isobar degrees of freedom. The form factors are evaluated at the one-loop level, where particular emphasis is put on the use of on-shell masses in the loop expressions. Our results are presented in terms of a novel set of basis functions that generalize the Passarino-Veltman scheme to the case where power-counting violating structures are to be subtracted. The particularly important role of the isobar degrees of freedom is emphasized. We obtain a significant and simultaneous fit to the available lattice QCD results based on flavor SU(2) ensembles for the baryon masses and form factors up to pion masses of about 500 MeV. Our fit includes sizeable finite volume effects that are implied by using in-box values for the hadron masses entering our one-loop expressions. We conclude that from flavor SU(2) ensembles it appears not possible to predict the empirical form factor at the desired precision. Effects from strange quarks are expected to remedy the situation. Published by the American Physical Society 2024

A positive metric over DGKT vacua

We study the notion of a metric over the space of AdS solution in string theory, leading to an associated distance between them. Such a distance is the idea underlying the AdS distance conjecture. We utilise the previously developed prescription for extracting such a metric: taking an off-shell quadratic variation of the string theory effective action and then evaluating it over the space of on-shell solutions. It was shown that this prescription leads to a well-defined positive metric over M-theory Freund-Rubin vacua. In this work, we use the same prescription to calculate the metric over type IIA DGKT vacua. These are much more involved, they have multiple flux parameters and exhibit scale separation. While it remains an open question whether these vacua exist as fully localised solutions of string theory, they are well-defined within the four-dimensional effective theory, which is all that is required for the calculation. We find that they also have a positive metric over them. Interestingly, this metric turns out to be independent of the many flux parameters in the solution, similarly to what happens for metrics over scalar field spaces. This non-trivial flux cancellation, as well as results from explicit vacua, lead us to propose a Swampland condition: that the metric over the space of vacua in quantum gravity, as defined by the above prescription, is always positive.

Dark matter reconstruction from stellar orbits in the Galactic centre

Context. Current constraints on distributed matter in the innermost Galactic centre (such as a cluster of faint stars and stellar remnants, dark matter, or a combination thereof) based on the orbital dynamics of the visible stars closest to the central black hole typically assume simple functional forms for the distributions. Aims. We aim to take a general model-agnostic approach in which the form of the distribution is not constrained by prior assumptions on the physical composition of the matter. This approach yields unbiased, entirely observation-driven fits for the matter distribution and places constraints on our ability to discriminate between different density profiles (and consequently between physical compositions) of the distributed matter. Methods. We constructed a spherical shell model with the flexibility to fit a wide variety of physically reasonable density profiles by modelling the distribution as a series of concentric mass shells. We tested this approach in an analysis of mock observations of the star S2. Results. For a sufficiently large and precise data set, we find that it is possible to discriminate among several physically motivated density profiles. However, for data coming from current and expected next generation observational instruments, the potential for profile distinction will remain limited by the precision of the instruments. Future observations will still be able to constrain the overall enclosed distributed mass within the apocentre of the probing orbit in an unbiased manner. We interpret this in the theoretical context of constraining the secular versus non-secular orbital dynamics. Conclusions. Our results show that while stellar data over multiple orbits of currently known stars will eventually yield model-agnostic constraints for the overall amount of distributed matter within the probe’s apocentre in the innermost Galactic centre, an unbiased model distinction made by determining the radial density profile of the distribution is, in principle, out of the measurement accuracy of the current and next-generation instruments. Constraints on dark matter models will therefore remain subject to model assumptions and will not be able to significantly downsize the zoo of candidate models.

Partial-wave projection of the one-particle exchange in three-body scattering amplitudes

As the study of three-hadron physics from lattice QCD matures, it is necessary to develop proper analysis tools in order to reliably study a variety of phenomena, including resonance spectroscopy and nuclear structure. Reconstructing the three-particle scattering amplitude requires solving integral equations, which can be written in terms of data-constrained dynamical functions and physical on shell quantities. The driving term in these equations is the so-called one-particle exchange, which leads to a kinematic divergence for particles on mass shell. A vital component in defining three-particle amplitudes with definite parity and total angular momentum, which are used in spectroscopic studies, is to project the one-particle exchange into definite partial waves. We present a general procedure to construct exact analytic partial-wave projections of the one-particle exchange contribution for any system composed of three spinless hadrons. Our result allows one full control over the analytic structure of the projection, which we explore for some low-lying partial waves with applications to three pions. Published by the American Physical Society 2024

Dimensional regularization and two-loop vacuum polarization operator: Master integrals, analytic results, and energy shifts

We present a complete reevaluation of the irreducible two-loop vacuum-polarization correction to the photon propagator in quantum electrodynamics, i.e. with an electron-positron pair in the fermion propagators. The integration is carried out by reducing the integrations to a limited set of master integrals, which are calculated using integration-by-parts identities. Dimensional regularization is used in D=4−2ε dimensions, and on-mass shell renormalization is employed. The one-loop effect is given to order ε, to be combined with the 1/ε divergence of the two-loop amplitude. Master integrals are given. Final evaluations of two-loop energy shifts for 1S, 2S, and 2P states are done analytically, and results are presented, with an emphasis on muonic hydrogen. For relativistic Dirac-Coulomb reference states, higher-order coefficients are obtained for the Zα-expansion. We compare the results obtained to the existing literature. Published by the American Physical Society 2024