Angular Momentum Parameter Research Articles

Structure and Rotation of Young Massive Star Clusters in a Simulated Dwarf Starburst

Abstract We analyze the three-dimensional shapes and kinematics of the young star cluster population forming in a high-resolution griffin project simulation of a metal-poor dwarf galaxy starburst. The star clusters, which follow a power-law mass distribution, form from the cold phase interstellar medium with an initial mass function sampled with individual stars down to four solar masses at sub-parsec spatial resolution. Massive stars and their important feedback mechanisms are modeled in detail. The simulated clusters follow a surprisingly tight relation between the specific angular momentum and mass with indications of two sub-populations. Massive clusters (M cl ≳ 3 × 104 M ⊙) have the highest specific angular momenta at low ellipticities (ϵ ∼ 0.2) and show alignment between their shapes and rotation. Lower mass clusters have lower specific angular momenta with larger scatter, show a broader range of elongations, and are typically misaligned indicating that they are not shaped by rotation. The most massive clusters (M ≳ 105 M ⊙) accrete gas and protoclusters from a ≲100 pc scale local galactic environment on a t ≲ 10 Myr timescale, inheriting the ambient angular momentum properties. Their two-dimensional kinematic maps show ordered rotation at formation, up to v ∼ 8.5 km s−1, consistent with observed young massive clusters and old globular clusters, which they might evolve into. The massive clusters have angular momentum parameters λ R ≲ 0.5 and show Gauss–Hermite coefficients h 3 that are anti-correlated with the velocity, indicating asymmetric line-of-sight velocity distributions as a signature of a dissipative formation process.

Onset of spontaneous scalarization in spinning Gauss-Bonnet black holes

It has recently been proved numerically that spinning black holes in Einstein-scalar theories which are characterized by a nonminimal negative coupling of the scalar field to the Gauss-Bonnet invariant of the curved spacetime may develop exponentially growing instabilities. Intriguingly, it has been demonstrated that this tachyonic instability, which marks the onset of the spontaneous scalarization phenomenon in the Einstein-Gauss-Bonnet-scalar theory, characterizes spinning black holes whose dimensionless angular momentum parameter $\overline{a}\ensuremath{\equiv}a/M$ is larger than some critical value ${\overline{a}}_{\mathrm{crit}}\ensuremath{\simeq}0.505$. In the present paper we prove, using analytical techniques, that the critical rotation parameter which marks the boundary between bald Kerr black holes and hairy (scalarized) spinning black holes in the Einstein-Gauss-Bonnet-scalar theory is given by the exact dimensionless relation ${\overline{a}}_{\mathrm{crit}}=\frac{1}{2}$.

Rotation Curves in z ∼ 1–2 Star-forming Disks: Evidence for Cored Dark Matter Distributions

Abstract We report high-quality, Hα or CO rotation curves (RCs) to several R e for 41 large, massive, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy evolution (z ∼ 0.67–2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA. Most RC41 SFGs have reflection-symmetric RCs plausibly described by equilibrium dynamics. We fit the major axis position–velocity cuts using beam-convolved forward modeling generated in three dimensions, with models that include a bulge and turbulent disk component embedded in a dark matter (DM) halo. We include priors for stellar and molecular gas masses, optical light effective radii and inclinations, and DM masses from abundance-matching scaling relations. Two-thirds or more of the z ≥ 1.2 SFGs are baryon dominated within a few R e of typically 5.5 kpc and have DM fractions less than maximal disks (median 〈 f DM ( R e ) 〉 = 0.12 ). At lower redshift (z < 1.2), that fraction is less than one-third. DM fractions correlate inversely with the baryonic angular momentum parameter, baryonic surface density, and bulge mass. Inferred low DM fractions cannot apply to the entire disk and halo but more plausibly reflect a flattened, or cored, inner DM density distribution. The typical central “DM deficit” in these cores relative to Navarro–Frenk–White (NFW) distributions is ∼30% of the bulge mass. The observations are consistent with rapid radial transport of baryons in the first-generation massive gas-rich halos forming globally gravitationally unstable disks and leading to efficient build-up of massive bulges and central black holes. A combination of heating due to dynamical friction and AGN feedback may drive DM out of the initial cusps.

Relativistic accretion disc in tidal disruption events

ABSTRACT We construct a time-dependent relativistic accretion model for tidal disruption events (TDEs) with an α-viscosity and the pressure dominated by gas pressure. We also include the mass fallback rate $\dot{M}_\mathrm{ f}$ for both full and partial disruption TDEs, and assume that the infalling debris forms a seed disc in time tc, which evolves due to the mass addition from the infalling debris and the mass-loss via accretion on to the black hole. Besides, we derive an explicit form for the disc height that depends on the angular momentum parameter in the disc. We show that the surface density of the disc increases at an initial time due to mass addition, and then decreases as the mass fallback rate decreases, which results in a decrease in the disc mass Md with a late-time evolution of Md ∝ t−1.05 and t−1.38 for full and partial disruption TDEs, respectively, where t is the time parameter. The bolometric luminosity L shows a rise and decline that follows a power law at late times given by L ∝ t−1.8 and t−2.3 for full and partial disruption TDEs, respectively. Our obtained luminosity declines faster than the luminosity inferred using $L \propto \dot{M}_\mathrm{ f}$. We also compute the light curves in various spectral bands.

Instability and phase transitions of a rotating black hole in the presence of perfect fluid dark matter

In this paper, we study the thermodynamic features of a rotating black hole surrounded by perfect fluid dark matter. We analyze the critical behavior of the black hole by considering the known relationship between pressure and cosmological constant. We show that the black hole admits a first order phase transition and, both rotation and perfect fluid dark matter parameters have a significant impact on the critical quantities. We also introduce a new ad hoc pressure related to the perfect fluid dark matter and find a first order van der Waals like phase transition. In addition, using the sixth order WKB method, we investigate the massless scalar quasinormal modes (QNMs) for the static spherically symmetric black hole surrounded by dark matter. Using the finite difference scheme, the dynamical evolution of the QNMs is also discussed for different values of angular momentum and overtone parameters.

Rotating regular black holes in conformal massive gravity

In this paper, we use a suitable conformal rescaling to construct static and rotating regular black holes in conformal massive gravity. The new metric is characterized by the mass $M$, the "scalar charge" $Q$, the angular momentum parameter $a$, the "hair parameter" $\lambda$, and the conformal scale factor encoded in the parameter $L$. We explore the shadow images and the deflection angles of relativistic massive particles in the spacetime geometry of a rotating regular black hole. For $\lambda \neq 0$ and $Q > 0$, the shadow is larger than the shadow of a Kerr black hole. In particular, if $\lambda < 0$, the shadow radius increases considerably. For $\lambda \neq 0$ and $Q < 0$, the shadow is smaller than the shadow of a Kerr black hole. Additionally we put observational constraints on the parameter $ Q $ using the latest Event Horizon Telescope (EHT) observation of the supermassive black hole M87*. Lastly, using the Gauss-Bonnet theorem, we show that the deflection angle of massive particles is strongly affected by the parameter $L$. The deflection angle might be used to distinguish rotating regular black holes from rotating singular black holes.

Quasinormal modes of generalized black holes: δ-Kerr spacetime

The nonlinear superposition of the -metric and the Kerr metric results in a -Kerr metric that represents a deformed Kerr black hole with , where q > 0 is proportional to the nonrelativistic quadrupole moment of the collapsed configuration. We study this spacetime and determine q+ such that for q, 0 < q < q+ , the outer spacetime singularity remains a null hypersurface. In this case, -Kerr spacetime represents a generalized black hole, namely, an asymptotically flat, stationary and axisymmetric vacuum solution of general relativity for which the outer singularity is a closed null hypersurface. For an approximate variant of -Kerr spacetime characterized by mass M, quadrupole parameter q and angular momentum parameter a, where the latter two parameters are treated to first and second orders of approximation, respectively, we analytically determine the quasinormal mode (QNM) frequencies in the ray approach using the light-ring method as well as in the complementary wave approach for massless scalar field perturbations in the a = 0 limit. The QNM frequencies of -Kerr spacetime turn out to be nearly the same as those of the rotating Hartle–Thorne spacetime.

Enhanced cosmological perturbations and the merger rate of PBH binaries

The rate of merger events observed by LIGO/Virgo can be used in order to probe the fraction f of dark mater in the form of primordial black holes (PBH) . Here, we consider the merger rate of PBH binaries, accounting for the effect of cosmological perturbations on their initial eccentricity e. The torque on the binaries may receive significant contributions from a wide range of scales, that goes from the size of the horizon at the time when the binary forms, down to the co-moving size of the binary. Extrapolating the observed plateau in the power spectrum PΦ ≈ 10−9 from cosmological scales down to the co-moving size of binaries, the torque from perturbations is small. In this case, for f ≳ 10−2, the distribution of eccentricities is dominated by tidal torques from neighboring PBHs. On the other hand, in scenarios where PBH are formed from adiabatic perturbations, it is natural to expect an enhancement of PΦ at small scales, where it is poorly constrained observationally. The effect can then be quite significant. For instance, a nearly flat spectrum with amplitude PΦ ≳ 10−7 on scales smaller than ∼ 10 Mpc−1 gives a contribution ⟨j2⟩ ∼ 103 PΦ, where j = (1−e2)1/2 is the dimensionless angular momentum parameter of the binaries. This contribution can dominate over tidal torques from neighboring PBHs for any value of f. Current constraints allow for a power spectrum as large as PΦ ∼ 10−5 at the intermediate scales 103–105 Mpc−1, comparable to the co-moving size of the binaries at the time of formation. In particular, this can relax current bounds on the PBH abundance based on the observed LIGO/Virgo merger rate, allowing for a fraction f ∼ 10% of dark matter in PBH of mass ∼ 30 M⊙. We investigate the differential merger rate ΔΓ(m1,m2), as a function of the masses of the binary components, and the corresponding “universality” coefficient [1] α = −(m1+m2)2 ∂2 ln ΔΓ/∂m1∂m2. For an enhanced power spectrum with spectral index p we find that α ≈ 30/(32−7p) for 0 < p ≲ 2, and α ≈ 5/3 for p ≳ 2. Such values may lie well outside the narrow range α ≈ 1±0.05 characteristic of tidal forces from neighboring PBHs. We conclude that, given a large enough sample of events, merger rates may provide valuable information on the spectrum of primordial cosmological perturbations at currently uncharted lengthscales.

Major mergers between dark matter haloes – I. Predictions for size, shape, and spin

The structural properties of individual dark matter haloes, including shape, spin, concentration, and substructure, are linked to the halo's growth history, but the exact connection between the two is unclear. One open question, in particular, is the effect of major mergers on halo structure. We have performed a large set of simulations of binary equal-mass mergers between isolated haloes with various density profiles, to map out the relationship between the initial conditions and merger parameters and the structure of the final remnant. In this paper we describe our initial set-up and analysis methods, and report on the results for the size, shape, and spin of the merger remnant. The outcomes of mergers are most easily understood in terms of a scaled dimensionless energy parameter $\kappa$ and an angular momentum (or spin) parameter $\lambda$. We find that the axis ratio $c/a$ scales roughly linearly with energy $\kappa$ while the axis ratio $c/b$ scales linearly with spin $\lambda$. Qualitatively, mergers on radial orbits produce prolate remnants, while mergers on tangential orbits produce oblate remnants. The spin of the remnant can be predicted from angular momentum conservation, while the overall size changes as $\sim \kappa^{-5}$, as expected from self-similar scaling at constant mean density. We discuss potential cosmological applications for these simple patterns.

Remark on Remnant and Residue Entropy with GUP

In this article, close to the Planck scale, we discuss the remnant and residue entropy from a Rutz-Schwarzschild black hole in the frame of Finsler geometry. Employing the corrected Hamilton-Jacobi equation, the tunneling radiation of a scalar particle is presented, and the revised tunneling temperature and revised entropy are also found. Taking into account generalized uncertainty principle (GUP), we analyze the remnant stability and residue entropy based on thermodynamic phase transition. In addition, the effects of the Finsler perturbation parameter, GUP parameter, and angular momentum parameter on remnant and residual entropy are also discussed.

The Reissner\u2013Nordstr\xf6m black hole with the fastest relaxation rate

Numerous numerical investigations of the quasinormal resonant spectra of Kerr-Newman black holes have revealed the interesting fact that the characteristic relaxation times tau ({bar{a}},{bar{Q}}) of these canonical black-hole spacetimes can be described by a two-dimensional function {{bar{tau }}}equiv tau /M which increases monotonically with increasing values of the dimensionless angular-momentum parameter {bar{a}}equiv J/M^2 and, in addition, is characterized by a non-trivial (non-monotonic) functional dependence on the dimensionless charge parameter {bar{Q}}equiv Q/M. In particular, previous numerical investigations have indicated that, within the family of spherically symmetric charged Reissner–Nordström spacetimes, the black hole with {bar{Q}}simeq 0.7 has the fastest relaxation rate. In the present paper we use analytical techniques in order to investigate this intriguing non-monotonic functional dependence of the Reissner–Nordström black-hole relaxation rates on the dimensionless physical parameter {bar{Q}}. In particular, it is proved that, in the eikonal (geometric-optics) regime, the black hole with {bar{Q}}={{sqrt{51-3sqrt{33}}}over {8}}simeq 0.73 is characterized by the fastest relaxation rate (the smallest dimensionless relaxation time {{bar{tau }}}) within the family of charged Reissner–Nordström black-hole spacetimes.

Analytical description of shape transition in nuclear alternating parity bands**Supported by the RFBR (Moscow) (16-02-00068A) and the Russian Government Subsidy Program of the Competitive Growth of Kazan Federal University. S.G.Z. was partly supported by the National Key R&D Program of China (2018YFA0404402), the NSF of China (11525524, 11621131001, 11647601, 11747601, 11711540016), the CAS Key Research Program of Frontier Sciences (QYZDB-SSWSYS013),

The angular momentum dependencies of parity splitting and electric dipole transitions in the alternating parity bands of heavy nuclei have been analyzed. It is shown that these dependencies can be treated in a universal manner with a single critical angular momentum parameter, which characterizes phase transition from octupole vibrations to the stable octupole deformation. Using the simple but useful model of axially-symmetric reflection-asymmetric mode, the analytical expressions for parity splitting and electric dipole transitional moment have been obtained. The findings are in good agreement with the experimental data for various isotopes of Ra, Th, U, and Pu.

Gravitational lensing by rotating wormholes

In this paper the deflection angle of light by a rotating Teo wormhole spacetime is calculated in the weak limit approximation. We mainly focus on the weak deflection angle by revealing the gravitational lensing as a partially global topological effect. We apply the Gauss-Bonnet theorem (GBT) to the optical geometry osculating the Teo-Randers wormhole optical geometry to calculate the deflection angle. Furthermore we find the same result using the standard geodesic method. We have found that the deflection angle can be written as a sum of two terms, namely the first term is proportional to the throat of the wormhole and depends entirely on the geometry, while the second term is proportional to the spin angular momentum parameter of the wormhole. A direct observation using lensing can shed light and potentially test the nature of rotating wormholes by comparing with the black holes systems.

Complexity growth in minimal massive 3D gravity

We study the complexity growth by using complexity = action (CA) proposal in Minimal Massive 3D Gravity(MMG) model which is proposed for resolving the bulk-boundary clash problem of Topologically Massive Gravity(TMG). We observe that the rate of the complexity growth for BTZ black hole saturates the proposed bound by physical mass of the BTZ black hole in the MMG model, when the angular momentum parameter and the inner horizon of black hole goes to zero.

Study of Cold Fusion Reactions Using Collective Clusterization Approach**Supported by the Council of Scientific and Industrial Research (CSIR), in the Form of Research Project Grant No. 03(1341)/15/EMR-II, and to DST, New Delhi, for INSPIRE-Fellowship Grant No. DST/INSPIRE/03/2015/000199

Within the framework of the dynamical cluster decay model (DCM), the 1n evaporation cross-sections ( of cold fusion reactions (Pb and Bi targets) are calculated for –113 superheavy nuclei. The calculations are carried out in the fixed range of excitation energy , so that the comparative analysis of reaction dynamics can be worked out. First of all, the fission barriers (Bf) and neutron separation energies () are estimated to account the decreasing cross-sections of cold fusion reactions. In addition to this, the importance of hot optimum orientations of β2i-deformed nuclei over cold one is explored at fixed angular momentum and neck-length parameters. The hot optimum orientations support all the target-projectile (t,p) combinations, which are explored experimentally in the cold fusion reactions. Some new target-projectile combinations are also predicted for future exploration. Further, the 1n cross-sections are addressed for –113 superheavy nuclei at comparable excitation energies which show the decent agrement with experimental data upto nuclei. Finally, to understand the dynamics of higher-Z superheavy nuclei, the cross-sections are also calculated at maximum available energies around the Coulomb barrier and the effect of non-sticking moment of inertia () is also investigated at these energies.

Coulomb fields as perturbations of type D vacuum space-times

We consider a test, non-null electromagnetic field special in the sense that the principal null directions of the field lie along the two repeated principal null directions of the type D vacuum background. We prove that the special non-null field is a valid solution of the Maxwell equations on a type D background. This field behaves as $1/r^2$ and the only non-vanishing Maxwell scalar is $\phi_1$ so it can be called the Coulomb field. We show that the contribution to the energy and angular momentum fluxes of the Coulomb field vanishes at any surface of integration, on the type D vacuum backgrounds Kerr, Kerr-Taub-NUT, Taub-NUT, and Schwarzschild. Therefore this field does not lead to any perturbations of the mass and angular momentum parameters of these space-times.

On the effects of Orbital Angular Momentum (OAM) and impact parameters on (e, 2e) process on atoms by twisted electron

SynopsisWe present our theoretical study of (e, 2e) process on atoms by the twisted electron, with special emphasis given on the effects of OAM and impact parameters on TDCS.

Group theory, coherent states, and the N-dimensional oscillator

The isotropic harmonic oscillator in N dimensions is shown to have an underlying symmetry group O(2,1)X O(N)which implies a unique result for the energy spectrum of the system. Raising and lowering operators analogous to those of the one-dimensional oscillator are given for each value of the angular momentum parameter. This allows the construction of an infinite number of coherent states to be carried out. In the N=1 case there is a twofold family of coherent states, a particular linear combination of which coincides with the single set already well known for that case. Wave functions are readily derived which require only the solution of a first order differential equation, an attribute generally characteristic of group theoretical approaches.

Casimir effect in the Kerr spacetime with quintessence

We calculate the Casimir energy of a massless scalar field in a cavity formed by nearby parallel plates orbiting a rotating spherical body surrounded by quintessence, investigating the influence of the gravitational field on that energy, at zero temperature. This influence includes the effects due to the spacetime dragging caused by the source rotation as well as those ones due to the quintessence. We show that the energy depends on all the involved parameters, as source mass, angular momentum and quintessence state parameter, for any radial coordinate and polar angle. We show that at the north pole the Casimir energy is not influenced by the quintessential matter. At the equatorial plane, when the quintessence is canceled, the result obtained in the literature is recovered. Finally, constraints in the quintessence parameters are obtained from the uncertainty in the current measurements of Casimir effect.

Functional phases and angular momentum characteristics of Tkatchev and Kovacs

ABSTRACTUnderstanding the technical requirements and underlying biomechanics of complex release and re-grasp skills on high bar allows coaches and scientists to develop safe and effective training programmes. The aim of this study was to examine the differences in the functional phases between the Tkatchev and Kovacs skills and to explain how the angular momentum demands are addressed. Images of 18 gymnasts performing 10 Tkatchevs and 8 Kovacs at the Olympic Games were recorded (50 Hz), digitised and reconstructed (3D Direct Linear Transformation). Orientation of the functional phase action, defined by the rapid flexion to extension of the shoulders and extension to flexion of the hips as the performer passed through the lower vertical, along with shoulder and hip angular kinematics, angular momentum and key release parameters (body angle, mass centre velocity and angular momentum about the mass centre and bar) were compared between skills. Expected differences in the release parameters of angle, angular momentum and velocity were observed and the specific mechanical requirement of each skill were highlighted. Whilst there were no differences in joint kinematics, hip and shoulder functional phase were significantly earlier in the circle for the Tkatchev. These findings highlight the importance of the orientation of the functional phase in the preceding giant swing and provide coaches with further understanding of the critical timing in this key phase.