Negative Helicity Research Articles

New Data-Driven Constraints on the Sign of Gluon Polarization in the Proton.

Recently, the possible existence of negative gluon helicity Δg has been observed to be compatible with existing empirical constraints, including from jet production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider, and lattice QCD data on polarized gluon Ioffe time distributions. We perform a new global analysis of polarized parton distributions in the proton with new constraints from the high-x region of deep-inelastic scattering (DIS). A dramatic reduction in the quality of the fit for the negative Δg replicas compared to those with positive Δg suggests that the negative Δg solution cannot simultaneously account for high-x polarized DIS data along with lattice and polarized jet data.

Observation of Kinetic Alfvén Waves inside an Interplanetary Coronal Mass Ejection Magnetic Cloud at 1 au

Recent advancements have significantly enhanced our grasp of interplanetary coronal mass ejections (ICMEs) in the heliosphere. These observations have uncovered complex kinematics and structural deformations in ICMEs, hinting at the possible generation of magnetohydrodynamic (MHD) and kinetic-scale waves. While MHD-scale waves in magnetic clouds have been explored, understanding the dynamics of kinetic-scale mode waves remains challenging. This article demonstrates the first in situ observation of kinetic Alfvén waves (KAWs) within an ICME’s magnetic cloud, notably near the heliospheric current sheet–ICME interaction region, close to the reconnection exhaust. Analysis indicates a distinctive negative bump in the estimated normalized magnetic helicity (σ m = −0.38) around the gyrofrequency spread, indicating a right-handed polarization of the wave. Furthermore, examination across flow angle (θ VB) within the frequency domain reveals a specific zone (90°–135°) showcasing negative helicity fluctuations, confirming the presence of KAWs. Moreover, we noted a significant rise in temperature anisotropy in the vicinity, indicating the role of KAWs in plasma heating. Identifying KAW challenges established notions about ordered magnetic clouds and raises questions about energy transfer processes within these structures. This finding opens the door to a deeper understanding of energy transfer mechanisms within traditionally nondissipative regions and invites further exploration of low-beta plasma heating and the interactions between waves and particles in magnetic clouds.

Effects of streamwise rotation on helicity and vortex in channel turbulence

Helicity plays a key role in the evolution of vortex structures and turbulent dynamics. The helicity dynamics and vortex structures in streamwise-rotating channel turbulence are discussed in this paper using the helicity budget equation and the differentiated second-order structure function equation of helicity. Generally, rotation and Reynolds numbers exhibit opposing effects on the interscale helicity dynamics and the vortices. Under the buffer layer, the positions of the helicity peaks are proportional to the ratio between the Reynolds and rotation numbers. The mechanism is related to the opposing effects of convection and rotation. Rotation directly affects the helicity balance through the Coriolis term and corresponding pressure term. In the buffer layer, the scale helicity is negative at small scales but positive at large scales, which is mainly induced by the spatial effects (the production and the spatial turbulent convection) but reduced by interscale cascades. Examination of structures reveals the close association between scale helicity and streaks, with streak lift angles exhibiting an increase with rotation and a decrease with Reynolds numbers. In the log-law layer, the Coriolis terms and corresponding pressure terms are proportional to the rotation numbers but remain independent of the Reynolds numbers. The negative scale helicity is forward cascaded towards small scales. Generally, spanwise vortices in the log-law layer are related to sweep events and forward cascades. Our findings indicate that these spanwise vortices are suppressed by rotation but recover with increasing Reynolds numbers, aligning with the effects observed in the scale helicity balance.

Detector operators for celestial symmetries

This paper presents a systematic cataloging of the generators of celestial symmetries on phase space. Starting from the celestial OPEs, we first show how to extract a representation of the general-spin analog of the wedge subalgebra of w1+∞ on the phase space of massless matter fields of arbitrary helicity. These generators can be expressed as light-sheet operators that are quadratic in the matter fields at future or past null infinity. We next show how to extend these symmetries beyond the wedge. Doing so requires us to augment the quadratic operators with: 1) linear terms corresponding to primary descendants of the negative helicity gauge fields the matter modes couple to, and 2) a tower of higher-particle composite operator contributions. These modes can be realized as light-ray operators supported on generators of null infinity, but local on the celestial sphere. Finally, we construct a representation of the celestial symmetries that captures how the positive helicity gauge fields transform. We close by discussing how these celestial symmetries inform our choice of detector operators.

Investigation on effect of anti-cavitation edge on performance and leakage vortex characteristics of tubular turbine for ocean power generation

Anti-cavitation edge directly affects turbine runner performance and clearance leakage flow. This paper takes a tubular turbine as the object of study and uses the numerical simulation method of SST-CC turbulence model based on rotation and curvature correction to study the effect of anti-cavitation edge thickness on the turbine internal flow patterns and the flow characteristics of tip leakage vortex under different conditions. The results show that the high-altitude bubble concentrated area on the blade suction surface is reduced after installing the anti-cavitation edges. Meanwhile, the leakage volume decreases by 13.28% under the optimal condition, and the maximum leakage decreases by 37.72% under the off-design condition. The raised structure of the anti-cavitation edge can effectively push the tip leakage vortex (TLV) away from the blade suction surface and destroy the original vortex structure; the strength of tip separation vortex (TSV) is obviously reduced. The energy loss increasingly reduces with the increase of anti-cavitation edge thickness, and the loss reduction value is greater in the off-design condition. The small negative helicity vortex at the draft tube wall surface disappears. The above research results provide a certain reference for the performance optimization of tubular turbine.

Higher-spin Yang–Mills, amplitudes and self-duality

The existence of interacting higher-spin theories is tightly constrained by many no-go theorems. In this paper, we construct a chiral, higher-spin generalization of Yang–Mills theory in flat space which avoids these no-go theorems and has non-trivial tree-level scattering amplitudes with some higher-spin external legs. The fields and action are complex, so the theory is non-unitary and parity-violating, yet we find surprisingly compact formulae for all-multiplicity tree-level scattering amplitudes in the maximal helicity violating (MHV) sector, where the two negative helicity particles have identical but arbitrary spin. This is possible because the theory admits a perturbative expansion around its self-dual sector. Using twistor theory, we prove the classical integrability of this self-dual sector and show that it can be described on spacetime by an infinite tower of interacting massless scalar fields. We also give a twistor construction of the full theory and use it to derive the formula for the MHV amplitude.

All-order celestial OPE in the MHV sector

On-shell kinematics for gluon scattering can be parametrized with points on the celestial sphere; in the limit where these points collide, it is known that tree-level gluon scattering amplitudes exhibit an operator product expansion (OPE)-like structure. While it is possible to obtain singular contributions to this celestial OPE, getting regular contributions from both holomorphic and anti-holomorphic sectors is more difficult. In this paper, we use twistor string theory to describe the maximal helicity violating (MHV) sector of tree-level, four-dimensional gluon scattering as an effective 2d conformal field theory on the celestial sphere. By organizing the OPE between vertex operators in this theory in terms of soft gluon descendants, we obtain all-order expressions for the celestial OPE which include all regular contributions in the collinear expansion. This gives new, all-order formulae for the collinear splitting function (in momentum space) and celestial OPE coefficients (in the conformal primary basis) of tree-level MHV gluon scattering. We obtain these results for both positive and negative helicity gluons, and for any incoming/outgoing kinematic configuration within the MHV sector.

Magnetic helicity and free magnetic energy as tools for probing eruptions in two differently evolving solar active regions

Aims. We study the role of magnetic helicity and free magnetic energy in the initiation of eruptions in two differently evolving solar active regions (ARs). Methods. Using vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and a magnetic connectivity-based method, we calculate the instantaneous relative magnetic helicity and free magnetic energy budgets for several days in two ARs, AR11890 and AR11618, both with complex photospheric magnetic field configurations. Results. The ARs produced several major eruptive flares while their photospheric magnetic field exhibited different evolutionary patterns: primarily flux decay in AR11890 and primarily flux emergence in AR11618. Throughout much of their evolution, both ARs featured substantial budgets of free magnetic energy and of both positive (right-handed) and negative (left-handed) helicity. In fact, the imbalance between the signed components of their helicity was as low as in the quiet Sun and their net helicity eventually changed sign 14−19 h after their last major flare. Despite this incoherence, the eruptions occurred at times of net helicity peaks that were co-temporal with peaks in the free magnetic energy. The percentage losses, associated with the eruptive flares, in the normalized free magnetic energy were significant, in the range of ∼10−60%. For the magnetic helicity, changes ranged from ∼25% to the removal of the entire excess helicity of the prevailing sign, leading a roughly zero net helicity, but with significant equal and opposite budgets of both helicity senses. Respective values ranged from (0.3 − 2)×1032 erg and (1.3 − 20)×1042 Mx2 for energy and helicity losses. The removal of the slowly varying background component of the free energy and helicity (either the net helicity or the prevailing signed component of helicity) time series revealed that all eruption-related peaks of both quantities exceeded the 2σ levels of their detrended time series above the removed background. There was no eruption when only one or none of these quantities exceeded its 2σ level. Conclusions. Our results indicate that differently evolving ARs may produce major eruptive flares even when, in addition to the accumulation of significant free magnetic energy budgets, they accumulate large amounts of both left- and right-handed helicity without a strong dominance of one handedness over the other. In most cases, these excess budgets appear as localized peaks, co-temporal with the flare peaks, in the time series of free magnetic energy and helicity (and normalized values thereof). The corresponding normalized free magnetic energy and helicity losses can be very significant at certain times.

Helicity and vorticity in heavy-ion collisions at energies available at the JINR Nuclotron-based Ion Collider facility

Heavy-ion collisions at center-of-mass nucleon collision energies 4.5--11.5 GeV are analyzed within the parton-hadron-string dynamics (PHSD) transport model. Spectator nucleons are separated, and the transfer of the initial angular momentum of colliding nuclei to the fireball formed by participants is studied. The maximal angular momentum is carried by the fireball in gold-gold collisions with the impact parameter about 5 fm corresponding to centrality class 10--20%. The obtained participant distributions were fluidized and the energy and baryon number densities, temperature, and velocity fields are obtained in the Landau frame. It is shown that the velocity field has dominantly Hubble-like transversal and longitudinal expansion with the vortical motion being only a small correction on top of it. The vorticity field is calculated and illustrated in detail. The formation of two oppositely rotating vortex rings moving in opposite directions along the $z$ axis is demonstrated. Other characteristics of the vortical motion such as the Lamb vector field and the kinematic vorticity number are considered. The magnitude of the latter one is found to be smaller than that for the Poiseuille flow and close to the pure shear deformation corresponding to just a flattening of fluid cells. The field of hydrodynamic helicity, which is responsible for the axial vortex effect, is calculated. The separation of positive and negative helicities localized in upper and lower semiplanes with respect to the reaction plane is shown. It is proved that the areas with various helicity signs can be probed by the selection of $\mathrm{\ensuremath{\Lambda}}$ hyperons with positive and negative projections of their momenta orthogonal to the reaction plane.

Helicity characteristics of cyclonic vortexes and their effect on convection in a wide‐ranging extreme rainstorm in China

AbstractOn 20–22 July 2012, a severe rainstorm occurred in the Sichuan basin of Southwest China and in the Beijing area of North China. This rainstorm was related to the activities of a Tibetan Plateau vortex (TPV) and Southwest China vortex (SWCV). By using radiosonde, satellite brightness temperature, and NCEP_FNL data, we investigated the helicity characteristics nearly the vortexes and their effect on convection. Results showed that (1) strong precipitation in the Sichuan basin was mainly related to the interaction between the TPV and SWCV, while strong precipitation in the Beijing area was related to the northward movement of a cyclonic vortex caused by a split in the SWCV. (2) During the occurrence of the rainstorm, four mesoscale convection systems (MCSs) were observed. Their vertical structure showed a positive vorticity–negative divergence in the lower levels, and negative vorticity–positive divergence in the upper levels, accompanied by vertical upward movement. This was an important factor in the development and maintenance of MCSs, as well as one of the mechanisms for producing heavy precipitation. On this basis, we further discussed the effect of helicity on the MCSs in the atmospheric environment with rotational characteristics. Results showed that the increase in negative water vapour helicity and storm‐relative helicity were more likely to cause a strong development of MCSs.

The connection between the equatorial temperature bias and north–south helicity segregation in numerical simulations of the geodynamo

SUMMARY In recent numerical simulations of the geodynamo the dynamo action is driven, primarily, by the effects of helicity, with differential rotation playing only a secondary role. These dynamos display a number of robust features, such as: (i) thin convective columns outside the tangent cylinder whose azimuthally averaged helicity, $\langle h \rangle = \langle {{{\bf u}} \cdot \nabla \times {{\bf u}}} \rangle $, is left-handed in the north and right-handed in the south, (ii) approximately 2-D motion in the equatorial regions, with negligible axial velocity,$\langle {{u}_z} \rangle \approx 0$, (iii) positive radial current at mid-latitudes and negative radial current in the equatorial regions, (iv) a radial outflow in the equatorial regions and (v) elevated temperatures near the equator. We seek the relationship between all five of these observations. First, we note that $\langle {{u}_z} \rangle \approx 0$ near the equator follows from the skew-symmetric distribution of helicity, while a negative radial current at the equator is a generic feature of helicity-driven dynamos which have positive (negative) helicity in the south (north). Next, we confirm an earlier suggestion that the equatorial outflow is driven by Lorentz forces associated with the negative radial current. Crucially, however, this outflow does not account for the elevated equatorial temperatures. Rather, the high temperature near the equator is primarily a consequence of anisotropic turbulent diffusion, which preferentially carries heat radially outward along the equator, this anisotropy being a consequence of the (approximately) 2-D flow near the equator. In short, we show that the high equatorial temperatures are a direct consequence of the skew-symmetric distribution of helicity. Finally, we recall that the high equatorial temperatures can themselves explain the observed helicity distribution, as buoyant anomalies near the equator trigger inertial waves which carry negative helicity upward and positive helicity downward. Thus, there is a direct, two-way coupling between the high equatorial temperatures and the helicity distribution.

Temporal Behaviors of Magnetic Helicity Injections by Self and Mutual Sunspot Rotations

Magnetic helicity is a physical parameter used to quantify the complexity of magnetic fields, providing an indication of the energy state in the coronal magnetic structure. We investigate the temporal evolution of magnetic helicity and its relationship to the occurrence of a variety of flares in the solar active region NOAA 12297, which was well observed using the Solar Dynamics Observatory/Helioseismic and Magnetic Imager in 2015 March. The active region produced many M-class flares and an X-class flare in two distinctive areas, both of which had a similar magnetic evolution, i.e., the opposite polarity of an emerging flux developed beside a preexisting sunspot, but exhibited flares with different magnitudes and frequencies. We derived the spatiotemporal evolution of the magnetic helicity injections and evaluated how spinning and braiding helicity injections evolved with time in the two areas. In one area, we observed a remarkable evolution, in which a negative spinning helicity injection in the preexisting sunspot increased in a positive helicity system, followed by the occurrence of the X-class flare. The negative helicity injection was clearly caused by the flux emergence that developed along the outer edge of the preexisting sunspot. The other area showed positive braiding helicity injections, with spinning helicity injections fluctuating concurrently with flux emergence, changing their signs several times, i.e., variable energy, and helicity input. The observed temporal behaviors of the helicity injections may explain different types of flare occurrences in the regions.

Cascade conditions in electron magneto-hydrodynamic turbulence

The basic features of electron whistler waves can be described by electron magneto-hydrodynamics. In terms of this model, we discuss criteria and relevant parameter ranges for dual and forward cascades in electron whistler turbulence. It is an advantage to use the set of eigenfunctions for the “curl” operator in the analysis. It is demonstrated that three wavemodes with same helicity support a dual cascade as know also from spatially two dimensional turbulence, while modes with mixed helicities include the classical cascade of energy from long to shorter wavelengths. The analysis is based on the conservation of energy and magnetic helicity during the wave interactions. For stationary conditions in large closed systems, a detailed balance can be expected. It is, however, possible for large-scale self-organized structures to develop as transient phenomena. These can be found when solving initial value problem with a strong imbalance of positive and negative helicities. For plasmas in nature or laboratory, similar conditions can occur when the system has boundary conditions with preference for emission of oscillations with one sign of helicity.

Evolution of an Emerging Anti-Hale Region and its Associated Eruptive Solar Flares in NOAA AR 12882

Solar active regions that violate the Hale–Nicholson rule are rare, but once formed, they tend to be flare-productive. In this letter, we investigated the evolution of an anti-Hale region newly emerging from the active region AR 12882 with a regular Hale distribution. The entire active region became very active, producing two eruptive flares within 48 hr after the emergence of the anti-Hale region. Strong photospheric shear motions appeared in this anti-Hale region, changing its tilt angle from the north–south direction to the east–west direction. The flux emergence and shearing motions continuously injected magnetic energy and negative magnetic helicity into the upper atmosphere. Meanwhile, the upper coronal structure changed from double J-shaped to reverse S-shaped, forming a magnetic flux rope lying above the anti-Hale region. This magnetic flux rope erupted successfully, then re-formed and erupted successfully again, producing a C2.7 flare and an M1.6 flare, respectively. Moreover, a large cusp structure was observed to form next to the flaring region after the M1.6 flare. Accordingly, we conclude that the evolution of the emerging anti-Hale region provides sufficient magnetic energy and helicity for the flares, and the interaction between the emerging anti-Hale region and the preexisting Hale active region eventually promotes the flares to be eruptive.

Transfers of energy and helicity in helical rotating turbulence

Helical rotating turbulence is a chiral and anisotropic flow. The energy and helicity transfers of helical rotating turbulence are studied in this paper. First, we discuss the antisymmetry and conservation of energy and helicity transfers. There are three expressions for helicity transfers due to the commutability of differential operators. The first expression is derived here. The second expression violates antisymmetry, and the third one introduces non-physical effects. The relations of these expressions are discussed in detail, including those about the sum of all triads and partial triads, as well as those about helical wave decomposition. Through direct numerical simulations, we find that helicity can reduce inverse energy cascades. The inhibition is mainly associated with transhelical energy fluxes and the interactions of two-dimensional modes. The inverse cascades of decomposed energy fluxes are related to the two-dimensionalization. For helicity, rotation does not affect the total helicity flux but generally suppresses the decomposed helicity fluxes. Positive homochiral and negative heterochiral helicity fluxes are associated with corresponding positive anisotropic transfers. Notably, the transhelical helicity fluxes increase the amplitudes of both positive and negative helicity, which is related to the chirality polarization.

Recognition of objects through symplectic capacities

We prove that the generalized symplectic capacities recognize objects in symplectic categories whose objects are of the form (M,ω), such that M is a compact and 1-connected manifold, ω is an exact symplectic form on M, and there exists a boundary component of M with negative helicity. The set of generalized symplectic capacities is thus a complete invariant for such categories. This answers a question by Cieliebak, Hofer, Latschev, and Schlenk. It appears to be the first result concerning this question, except for recognition results for manifolds of dimension 2, ellipsoids, and polydiscs in R4. Strikingly, our result holds more generally for differential form categories. Recognition of objects is therefore not a symplectic phenomenon.We also prove a version of the result for normalized capacities.

Ambidextrous light transforms for celestial amplitudes

Low multiplicity celestial amplitudes of gluons and gravitons tend to be distributional in the celestial coordinates z, overline{z} . We provide a new systematic remedy to this situation by studying celestial amplitudes in a basis of light transformed boost eigenstates. Motivated by a novel equivalence between light transforms and Witten’s half-Fourier transforms to twistor space, we light transform every positive helicity state in the coordinate z and every negative helicity state in overline{z} . With examples, we show that this “ambidextrous” prescription beautifully recasts two- and three-point celestial amplitudes in terms of standard conformally covariant structures. These are used to extract examples of celestial OPE for light transformed operators. We also study such amplitudes at higher multiplicity by constructing the Grassmannian representation of tree-level gluon celestial amplitudes as well as their light transforms. The formulae for n-point Nk−2MHV amplitudes take the form of Euler-type integrals over regions in Gr(k, n) cut out by positive energy constraints.

Sizable time-reversal violating effects in bottom baryon decays

We study time-reversal (T) asymmetries in the charmless two-body decays of antitriplet bottom baryons. We find that in Bb → BnP with Bb = ( {Xi}_b^{-} , {Xi}_b^0 , Λb) and Bn(P) a octet baryon (pseudoscalar meson), the positive and negative helicity amplitudes are both sizable, resulting in the large T-violating effects. Particularly, the T-odd parameters, βw, for the color-enhanced channels are expected to be around −40% and 25% in b → s and b → d transitions for the standard model, which can be measured by the experiments at LHCb, respectively. On the other hand, in Bb → BnV(γ) with V(γ) a vector meson (photon), the decays are predominated by a single helicity amplitude, and the T violating effects by the correlations among spins are suppressed. We also explore the T violating observables for the Ξb decays based on the angular distributions.

Successive injection of opposite magnetic helicity: evidence for active regions without coronal mass ejections

ABSTRACT Magnetic helicity (MH) is a measure of twist and shear of magnetic field. MH is injected in the active region (AR) corona through photospheric footpoint motions causing twisted and sheared magnetic fields. From the conservation property of the helicity, it was conjectured that an already twisted flux rope (FR) with continuous injection of MH inevitably erupts to remove the excess accumulated coronal helicity. Therefore, understanding the nature and evolution of the photospheric helicity flux transfer is crucial to reveal the intensity of the flare/coronal mass ejection (CME) activity. Using the time-sequence vector magnetograms of Helioseismic Magnetic Imager, we study the evolution of MH injection in emerging AR 12257. The photospheric flux motions in this AR inject positive helicity in the first 2.5 days followed by negative helicity later. This successive injection of opposite helicity is consistent with the sign of mean force-free twist parameter (αav), orientation of magnetic tongues. Also, the extrapolated AR magnetic structure exhibits transformation of global shear without a twisted FR in the core of the AR. No CMEs are launched from this AR but C-class flaring activity is observed predominantly in the second half of the evolution period. The ARs with sign reversal of the MH injection are not favourable to twisted FR formation with excess coronal helicity, and therefore, are important to identify CME-less ARs readily. A possible scenario in these ARs is that when one sign of helicity flux is replaced by opposite sign, the magnetic field of different connectivity with opposite shear undergoes reconnection at different scales giving rise to both intermittent flares and enhanced coronal heating.

A new Wilson line-based action for gluodynamics

We perform a canonical transformation of fields that brings the Yang-Mills action in the light-cone gauge to a new classical action, which does not involve any triple-gluon vertices. The lowest order vertex is the four-point MHV vertex. Higher point vertices include the MHV and overline{mathrm{MHV}} vertices, that reduce to the corresponding amplitudes in the on-shell limit. In general, any n-leg vertex has 2 ≤ m ≤ n − 2 negative helicity legs. The canonical transformation of fields can be compactly expressed in terms of path-ordered exponentials of fields and their functional derivative. We apply the new action to compute several tree-level amplitudes, up to 8-point NNMHV amplitude, and find agreement with the standard methods. The absence of triple-gluon vertices results in fewer diagrams required to compute amplitudes, when compared to the CSW method and, obviously, considerably fewer than in the standard Yang-Mills action.