Orientation Of Angular Momentum Research Articles

Early Evolution of Spin Direction in Dark Matter Halos and the Effect of the Surrounding Large-scale Tidal Field* *Thesis work conducted at Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Córdoba, Argentina. † † PhD Thesis directed by Manuel Merchán; PhD Degree awarded 2023 July 31.

It is usually assumed that the angular momentum (AM) of dark matter halos arises during the linear stages of structure formation, as a consequence of the coupling between the proto-haloes’ shape and the tidal field produced by their surrounding density perturbations. This approach, known as linear tidal torque theory (TTT), has been shown to make fairly good predictions about the mean evolution of both the AM amplitude and orientation up to approximately the time when the proto-haloes collapse. After this point, proto-haloes are increasingly affected by nonlinear processes that are not taken into account by the model. However, it has been seen in numerical simulations that, even at very early stages, the AM of proto-haloes is systematically reoriented toward perpendicularity with respect to the forming cosmic filaments, in contradiction with the fixed direction expected from the TTT. In this work we present a novel analytical approach that introduces an anisotropic scaling factor to the standard TTT equations, which allows the AM orientation to change in time, even during the linear regime. The amplitude and direction of this shift depend on the large scale tidal field around the forming proto-haloes. Our results significantly improve the predictions for the AM direction up to the time of protohalo collapse and, in some cases, even further in time.

Spatiotemporal coupling induced controllable orientation of photonic orbital angular momentum at subwavelength scale.

Recently, the emergence of transverse orbital angular momentum (OAM) as a novel characteristic of light has captured substantial attention, and the significance of adjustable OAM orientation has been underscored due to its pivotal role in the interaction between light and matter. In this work, we introduce a novel approach to manipulate the orientation of photonic OAM at subwavelength scales, leveraging spatiotemporal coupling. By tightly focusing a wavepacket containing dual spatiotemporal vortices and a spatial vortex through a high numerical aperture lens, the emergence of intricate coupling phenomena leads to entangled and intricately twisted vortex tunnels. As a consequence, the orientation of spatial OAM deviates from the conventional light axis. Through theoretical scrutiny, we unveil that the orientation of photonic OAM within the focal field is contingent upon the signs of the topological charges in both spatiotemporal and spatial domains. Additionally, the absolute values of these charges govern the precise orientation of OAM within their respective quadrants. Moreover, augmenting the pulse width of the incident light engenders a more pronounced deflection angle of photonic OAM. By astutely manipulating these physical parameters, unparalleled control over the spatial orientation of OAM becomes achievable. The augmented optical degrees of freedom introduced by this study hold considerable potential across diverse domains, including optical tweezers, spin-orbit angular momentum coupling, and quantum communication.

Highly localized continuous wave optical vortex with controllable orbital angular momentum orientation and topological charge.

We report an approach to simultaneously control orbital angular momentum (OAM) orientation and topological charge in highly localized optical vortices by employing a 4π focusing system. The required continuous wave illumination field in the pupil planes is derived by superimposing the radiation pattern of only one dipole placed at the focal point of the high numerical aperture lens and the corresponding tailored spiral phase factor. The topological charge and OAM orientation of the obtained focused fields are quantitatively evaluated based on the focal field distributions calculated by the Richards-Wolf vector diffraction integration theory. Results show that the OAM of the generated optical vortices can be tailored by changing the oscillation orientation of the mimic dipole and the topological charge of the superimposed spiral phase term. The presented method may find potential applications in optical trapping, optical tweezers, light-matter interaction, etc.

Evolution of the chiral rotation mode in rhodium isotopes

Self-consistent solutions for the chiral rotation in the rhodium isotopes $^{102--107}\mathrm{Rh}$ are obtained within the three-dimensional tilted axis cranking covariant density functional theory. The orientation of angular momenta is determined self-consistently by minimizing the total Routhian surface calculations with respect to the azimuth angle $\ensuremath{\varphi}$ and polar angle $\ensuremath{\theta}$ for a given rotational frequency. It is found that when neutrons are added the critical rotational frequency ${\ensuremath{\omega}}_{\text{crit}}$ of the appearance of chiral aplanar rotation decreases, which can be attributed to the neutrons in $(gd)$ shells having smaller and larger angular momentum components along the short and medium axes, respectively. The theoretical results agree well with the experimental energy spectra, electromagnetic transition probabilities, as well as the kinetic and dynamic moments of inertia.

Spatiotemporal optical vortices with arbitrary orbital angular momentum orientation by astigmatic mode converters

Abstract We generate a spatiotemporal optical vortex (STOV) with tunable orbital angular momentum (OAM) orientation by a simple lens system. We utilize a cylindrical lens system, which is an astigmatic mode converter, to add longitudinal angular momentum to tilt the purely transverse OAM in an arbitrary direction. The amount of tilt is tunable by adjusting the lens system, and thus the OAM direction is continuously adjustable. STOVs with adjustable OAM directions have been verified theoretically and experimentally. We believe such direction controllable OAMs will enrich future applications.

Spatial Orientations of Angular Momentum Vectors of Galaxies in Supercluster S [247+040+0029] and Substructures

We present an analysis of spatial orientations of 1331 galaxies in the supercluster S [247+040+0029]. The main goal of this work is to search for a new substructure candidate and examine the orientation of angular momentum in the framework of three different scenarios (hierarchy, pancake, and primordial vorticity models) using “position angle-inclination method”, and to test the dependence on magnitude with the angular momentum orientations and their projections. We identified five substructures studying number density contour map with considerably high concentration of galaxies. Using random simulation method to remove the selection effect on database, we carried out expected isotropic distribution using cosmological principle. We then used three statistical tests: Chi-square, Auto-correlation, and Fourier to identify isotropy between observed and expected isotropic distributions. We varied radius in the range 0.3° to 1.0° to find substructures in supercluster. From this we found five sub-structures when taking radius 0.3° and two substructures for 1.0° radius in the number density counter maps of galaxies. By analyzing the result obtained through statistical tests, we are able to conform that evolution of galaxy in the supercluster and substructures supports “Hierarchy model" giving the angular momentum of galaxies in the large scale structure tends to be oriented random with respect to the reference coordinate system.

Controlling the degree of rotational directionality in laser-induced molecular dynamics

We demonstrate experimentally a method of varying the degree of directionality in laser-induced molecular rotation. To control the ratio between the number of clockwise and counter-clockwise rotating molecules (with respect to a fixed laboratory axis), we change the polarization ellipticity of the laser field of an optical centrifuge. The experimental data, supported by the numerical simulations, show that the degree of rotational directionality can be varied in a continuous fashion between unidirectional and bidirectional rotation. The control can be executed with no significant loss in the total number of rotating molecules. The technique could be used for studying the effects of orientation of the molecular angular momentum on molecular collisions and chemical reactions. It could also be utilized for controlling magnetic and optical properties of gases, as well as for the enantioselective detection of chiral molecules.

The Formation of Supermassive Black Holes at Early Universe

The high-redshift universe is now the frontier of modern astronomy, and is the key object for current and near-future telescopes. The high-redshift quasars put a tight constraint on existing BH growth model, as it is challenging to form a 1010 M⊙ BH at z∼6.In this work, we relax the widely-adopted Salpeter BH growth model, to consider a more realistic path. We consider the variation in the mass and angular momentum orientation of gas supply (i.e. through ∊L and n), as well as the change in accretion mode (hot versus cold). Moreover, the conventionally considered BH spin impact on the radiative efficiency ∊M is also taken into account. Our key results can be summarized as follows. Firstly, sufficient gas supply (larger in ∊L) is obviously a key factor to make the BH grow efficiently. Also, The BH spin (a*), through the radiative efficiency ∊M, has a dominant impact on the BH growth, i.e., those high-redshift quasars with MBH > 1010 M⊙ should be formed in a chaotic gas supply situation, where the angular momentum orientation of the gas is random. Finally, through analyzing the most realistic accretion model, we find that the only existing model of seed BH is through the direct collapse, driven by either dynamical processes or thermodynamics

Binary white dwarfs and decihertz gravitational wave observations: From the Hubble constant to supernova astrophysics

Context. Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double degenerate scenario, they have been suggested to be possible progenitors of supernovae (SNe) Type Ia events. Aims. In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source’s luminosity distance, and on other binary’s parameters, such as the angular momentum orientation. Methods. We explore the possibility of coincident detections of gravitational and electromagnetic signals; the latter comes from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow one to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles. Results. We find that decihertz gravitational wave interferometers can measure the luminosity distance with relative accuracy better than 1% for binaries at 100 Mpc. We show how multimessenger observations can put strong constraints on the Hubble constant, which are tighter than current bounds at low redshift, and how they can potentially shed new light on the differences with early-universe measurements.

Cloudlet capture by transitional disk and FU Orionis stars

After its formation, a young star spends some time traversing the molecular cloud complex in which it was born. It is therefore not unlikely that, well after the initial cloud collapse event which produced the star, it will encounter one or more low mass cloud fragments, which we call “cloudlets” to distinguish them from full-fledged molecular clouds. Some of this cloudlet material may accrete onto the star+disk system, while other material may fly by in a hyperbolic orbit. In contrast to the original cloud collapse event, this process will be a “cloudlet flyby” and/or “cloudlet capture” event: A Bondi–Hoyle–Lyttleton type accretion event, driven by the relative velocity between the star and the cloudlet. As we will show in this paper, if the cloudlet is small enough and has an impact parameter similar or less than GM*/v∞2 (with v∞ being the approach velocity), such a flyby and/or capture event would lead to arc-shaped or tail-shaped reflection nebulosity near the star. Those shapes of reflection nebulosity can be seen around several transitional disks and FU Orionis stars. Although the masses in the those arcs appears to be much less than the disk masses in these sources, we speculate that higher-mass cloudlet capture events may also happen occasionally. If so, they may lead to the tilting of the outer disk, because the newly infalling matter will have an angular momentum orientation entirely unrelated to that of the disk. This may be one possible explanation for the highly warped/tilted inner/outer disk geometries found in several transitional disks. We also speculate that such events, if massive enough, may lead to FU Orionis outbursts.

Collisional dissipation of the laser-induced alignment of ethane gas: Energy corrected sudden quantum model.

We present the first quantum mechanical model of the collisional dissipation of the alignment of a gas of symmetric-top molecules (ethane) impulsively induced by a linearly polarized non-resonant laser field. The approach is based on use of the Bloch model and of the Markov and secular approximations in which the effects of collisions are taken into account through the state-to-state rates associated with exchanges among the various rotational states. These rates are constructed using the Energy Corrected Sudden (ECS) approximation with (a few) input parameters obtained independently from fits of the pressure-broadening coefficients of ethane absorption lines. Based on knowledge of the laser pulse characteristics and on these rates, the time-dependent equation driving the evolution of the density matrix during and after the laser pulse is solved and the time dependence of the so-called "alignment factor" is computed. Comparisons with measurements, free of any adjusted parameter, show that the proposed approach leads to good agreement with measurements. The analysis of the ECS state-to-state collisional rates demonstrates that, as in the case of linear molecules, collision-induced changes of the rotational angular momentum orientation are slower than those of its magnitude. This explains why the collisional decay of the permanent component of the alignment is significantly slower than that of the amplitudes of the transient revivals in both experimental and computed results. It is also shown that, since intermolecular forces within C2H6 colliding pairs weakly depend on rotations of the molecules around their C-C bond, the dissipation mechanism of the alignment in pure ethane is close to that involved in linear molecules.

The impact of non-ideal effects on the circumstellar disk evolution and their observational signatures

AbstractIt has been recognized that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for the circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the disk, which enables the formation of the circumstellar disk (e.g., Tsukamoto et al. 2015b). They set an upper limit to the magnetic field strength of ∼ 0.1 G around the disk (Masson et al. 2016). The Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum. This suggests that the bimodal evolution of the disk size possibly occurs in the early disk evolutionary phase (Tsukamoto et al. 2015a, Tsukamoto et al. 2017). Hall effect and ambipolar diffusion imprint the possibly observable characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect forms a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100–1000 au and a recent observation actually infers such a structure (Takakuwaet al. 2018). Ambipolar diffusion causes the significant ion-neutral drift in the envelopes. Our simulations show that the drift velocity of ion could become 100-1000 ms–1.

The origin of kinematically distinct cores and misaligned gas discs in galaxies from cosmological simulations

Integral field spectroscopy surveys provide spatially resolved gas and stellar kinematics of galaxies. They have unveiled a range of atypical kinematic phenomena, which require detailed modelling to understand. We present results from a cosmological simulation that includes stellar and active galactic nucleus (AGN) feedback. We find that the distribution of angles between the gas and stellar angular momenta of galaxies is not affected by projection effects. We examine five galaxies (≈6 per cent of well resolved galaxies) that display atypical kinematics; two of the galaxies have kinematically distinct cores (KDC), while the other three have counter-rotating gas and stars. All five form the majority of their stars in the field, subsequently falling into cosmological filaments where the relative orientation of the stellar angular momentum and the bulk gas flow leads to the formation of a counter-rotating gas disc. The accreted gas exchanges angular momentum with pre-existing co-rotating gas causing it to fall to the centre of the galaxy. This triggers low-level AGN feedback, which reduces star formation. Later, two of the galaxies experience a minor merger (stellar mass ratio ∼1/10) with a galaxy on a retrograde orbit compared to the spin of the stellar component of the primary. This produces the KDCs, and is a different mechanism than suggested by other works. The role of minor mergers in the kinematic evolution of galaxies may have been underappreciated in the past, and large, high-resolution cosmological simulations will be necessary to gain a better understanding in this area.

Dissipation dynamics of field-free molecular alignment for symmetric-top molecules: Ethane (C2H6).

The field-free molecular alignment of symmetric-top molecules, ethane, induced by intense non-resonant linearly polarized femtosecond laser pulses is investigated experimentally in the presence of collisional relaxation. The dissipation dynamics of field-free molecular alignment are measured by the balanced detection of ultrafast molecular birefringence of ethane gas samples at high pressures. By separating the molecular alignment into the permanent alignment and the transient alignment, the decay time-constants of both components are quantified at the same pressure. It is observed that the permanent alignment always decays slower compared to the transient alignment within the measured pressure range. This demonstrates that the propensity of molecules to conserve the orientation of angular momentum during collisions, previously observed for linear species, is also applicable to symmetric-top molecules. The results of this work provide valuable information for further theoretical understanding of collisional relaxation within nonlinear polyatomic molecules, which are expected to present interesting and nontrivial features due to an extra rotational degree of freedom.

Possible “umbrella”-like antimagnetic rotation mode in odd- A Pd101,103 and even-even Pd102,104

The tilted-axis cranking model based on covariant density functional theory is used to study the candidate antimagnetic rotation (AMR) bands in $^{101,102,103,104}\mathrm{Pd}$. The experimental energy spectra and $B(E2)$ values are reproduced well in the self-consistent and microscopic calculations. By investigating microscopically the composition and orientation of angular momentum, an ``umbrella''-like antimagnetic rotation (UAMR) mode resulting from the coupling of four ${g}_{9/2}$ proton holes to neutron particles is clearly illustrated for the first time.

Anisotropic kinetic energy release and gyroscopic behavior of CO2 super rotors from an optical centrifuge.

An optical centrifuge is used to generate an ensemble of CO2 super rotors with oriented angular momentum. The collision dynamics and energy transfer behavior of the super rotor molecules are investigated using high-resolution transient IR absorption spectroscopy. New multipass IR detection provides improved sensitivity to perform polarization-dependent transient studies for rotational states with 76 ≤ J ≤ 100. Polarization-dependent measurements show that the collision-induced kinetic energy release is spatially anisotropic and results from both near-resonant energy transfer between super rotor molecules and non-resonant energy transfer between super rotors and thermal molecules. J-dependent studies show that the extent and duration of the orientational anisotropy increase with rotational angular momentum. The super rotors exhibit behavior akin to molecular gyroscopes, wherein molecules with larger amounts of angular momentum are less likely to change their angular momentum orientation through collisions.

Circular dichroism of twisted photons in non-chiral atomic matter

We calculate the circular dichroism (CD) for the absorption of the twisted photons, or optical vortices, by atoms, caused by atomic excitation into discrete energy levels. The effects of photon spin on the rates and cross sections of atomic photo-excitation are considered. It is demonstrated that, although for electric dipole transitions the atomic excitation rates depend on the relative orientation of photon spin and orbital angular momentum (OAM), the resulting CD is zero. However, CD is nonzero for atomic transitions of higher multipolarity, and it is predicted to peak near the phase singularity in the optical vortex center. The effects remain large in a paraxial limit, where analytic expressions are provided. The predicted spin asymmetries are equivalent to OAM dichroism for the fixed photon spin.

On the Kinematics, Stability and Lifetime of Kinematically Distinct Cores: A Case Study

We present a case study of a early-type galaxy (ETG) hosting a kinematically distinct core (KDC) formed in a binary high resolution 1:1 spiral galaxy merger simulation. The runtime of the simulation is pushed up to 10 Gyr to follow the complete evolution of various physical properties. To investigate the origin of the KDC, the stellar component residing within the KDC is dissected, revealing that the rotational signal is purely generated by stars that belong to the KDC for at least 0 . 5 Gyr and are newly formed during the merging process. Following the orientation of the total stellar angular momentum of the KDC, we show that it performs a motion comparable to the precession of a gyroscope in a gravitational potential. We draw the conclusion that the motion of the KDC is a superposition of an intrinsic rotation and a global precession that gets gradually damped over cosmic time. Finally, the stability of the KDC over the complete runtime of the simulation is investigated by tracing the evolution of the widely used λ R parameter and the misalignment angle distribution. We find that the KDC is stable for about 3 Gyr after the merger and subsequently disperses completely on a timescale of ≈1.5 Gyr .

Study on Causes and Compensation for Speed Attenuation of a Spherical Superconducting Rotor

When the superconducting magnetic suspension device is in operation, the spherical superconducting rotor will keep rotating at a high speed above 200 Hz. It brings the rotor a large angular momentum and high orientation stability, which is one of the preconditions for achieving high accuracy of the device. However, in engineering practice, due to the influence of some factors, the speed of the rotor will decay, which affects the precision of the device. In this paper, main factors that arouse the speed attenuation of the rotor were analyzed. Experiments on speed attenuation with different pressures were carried out. Compensation for the error of the drift rate arising from speed attenuation was carried out after a drift test for the device. After compensation, the drift rate decreased by 4.95% compared with the value without compensation.

Stochastic template bank for gravitational wave searches for precessing neutron-star–black-hole coalescence events

Gravitational wave searches to date have largely focused on non-precessing systems. Including precession effects greatly increases the number of templates to be searched over. This leads to a corresponding increase in the computational cost and can increase the false alarm rate of a realistic search. On the other hand, there might be astrophysical systems that are entirely missed by non-precessing searches. In this paper we consider the problem of constructing a template bank using stochastic methods for neutron-star--black-hole binaries allowing for precession, but with the restrictions that the orientation of the total angular momentum of the binary is pointing towards the detector and that the neutron-star spin is negligible relative to that of the black-hole. We quantify the number of templates required for the search, and we explicitly construct the template bank. We show that despite the large number of templates, stochastic methods can be adapted to solve the problem. We quantify the parameter space region over which the non-precessing search might miss signals.