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Accurate Spin-Orbit Coupling and Intersystem Crossing by Relativistic Mixed-Reference Spin-Flip (MRSF)-TDDFT
No full textRelativistic MRSF-TDDFT is developed considering the spin-orbit coupling (SOC) within the mean-field approximation. The resulting SOC-MRSF faithfully reproduces the experiments with very high accuracy, which is also consistent with the values by four-component (4c) relativistic CASSCF and 4c-CASPT2 in the spin-orbit-energy splitting calculations of the C, Si and Ge atoms. Even for the fifth-row element Sn, the SOC-MRSF yielded accurate splittings (~3% error). In the SOC calculations of the molecular 4-thiothymine with a third-row element, SOC-MRSF values are in excellent agreement with those of SO-GMC-QDPT2 level, regardless of geometries and exchange-correlation functionals. The same SOC-MRSF predicted the anticipated chance of S₁ (n π*) -> T₁ (π π*) intersystem crossing, even in thymine with only second-row elements. With its accuracy and practicality, thus, SOC-MRSF is a promising electronic structure protocol in challenging situations such as nonadiabatic molecular dynamics (NAMD) incorporating both internal conversions and intersystem crossings in large systems
How Do Axisymmetric Black Holes Grow Monopole and Dipole Hair?
No full textWe study the dynamical formation of scalar monopole and dipole hair in scalar Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the spherically-symmetric mode of the dipole hair is completely determined by the product of the mass of the spacetime and the value of the monopole hair. We then show that the dynamics of the ℓ = 1 mode of the dipole hair is intimately tied to the appearance of the event horizon during axisymmetric collapse, which results in the radiation of certain modes that could have been divergent in the future of the collapse. We confirm these analytical predictions by simulating the gravitational collapse of a rapidly rotating neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical Chern-Simons theory. Our results, combined with those of Ref. [1], provide a clear physical picture of the dynamics of scalar monopole and dipole radiation in axisymmetric and spherical gravitational collapse in these theories
The HD 260655 system: Two rocky worlds transiting a bright M dwarf at 10 pc
No full textWe report the discovery of a multiplanetary system transiting the M0 V dwarf HD 260655 (GJ 239, TOI-4599). The system consists of at least two transiting planets, namely HD 260655 b, with a period of 2.77 d, a radius of Rb = 1.240 ± 0.023 R⊕, a mass of Mb = 2.14 ± 0.34 M⊕, and a bulk density of ρb = 6.2 ± 1.0 g cm−3, and HD 260655 c, with a period of 5.71 d, a radius of , a mass of Mc = 3.09 ± 0.48 M⊕, and a bulk density of g cm−3. The planets have been detected in transit by the Transiting Exoplanet Survey Satellite (TESS) mission and confirmed independently with archival and new precise radial velocities obtained with the HIRES and CARMENES instruments since 1998 and 2016, respectively. At a distance of 10 pc, HD 260655 has become the fourth closest known multitransiting planet system after HD 219134, LTT 1445 A, and AU Mic. Due to the apparent brightness of the host star (J = 6.7 mag), both planets are among the most suitable rocky worlds known today for atmospheric studies with the James Webb Space Telescope, both in transmission and emission
WALOP-South: a four-camera one-shot imaging polarimeter for PASIPHAE survey. Paper II – polarimetric modeling and calibration
No full textThe Wide-Area Linear Optical Polarimeter (WALOP)-South instrument is an upcoming wide-field and high accuracy optical polarimeter to be used as a survey instrument for carrying out the Polar-Areas Stellar Imaging in Polarization High-Accuracy Experiment program. Designed to operate as a one-shot four-channel and four-camera imaging polarimeter, it will have a field of view of 35 × 35 arcminutes and will measure the Stokes parameters l, q, and u in a single exposure in the Sloan Digital Sky Survey-r broadband filter. The design goal for the instrument is to achieve an overall polarimetric measurement accuracy of 0.1% over the entire field of view. We present here the complete polarimetric modeling of the instrument, characterizing the amount and sources of instrumental polarization. To accurately retrieve the real Stokes parameters of a source from the measured values, we have developed a calibration method for the instrument. Using this calibration method and simulated data, we demonstrate how to correct for instrumental polarization and obtain 0.1% accuracy in degree of polarization, p. In addition, we tested and validated the calibration method by implementing it on a table-top WALOP like test-bed polarimeter in the laboratory
Provably accurate simulation of gauge theories and bosonic systems
No full textQuantum many-body systems involving bosonic modes or gauge fields have infinite-dimensional local Hilbert spaces which must be truncated to perform simulations of real-time dynamics on classical or quantum computers. To analyze the truncation error, we develop methods for bounding the rate of growth of local quantum numbers such as the occupation number of a mode at a lattice site, or the electric field at a lattice link. Our approach applies to various models of bosons interacting with spins or fermions, and also to both abelian and non-abelian gauge theories. We show that if states in these models are truncated by imposing an upper limit Λ on each local quantum number, and if the initial state has low local quantum numbers, then an error at most ϵ can be achieved by choosing Λ to scale polylogarithmically with ϵ⁻¹, an exponential improvement over previous bounds based on energy conservation. For the Hubbard-Holstein model, we numerically compute a bound on Λ that achieves accuracy ϵ, obtaining significantly improved estimates in various parameter regimes. We also establish a criterion for truncating the Hamiltonian with a provable guarantee on the accuracy of time evolution. Building on that result, we formulate quantum algorithms for dynamical simulation of lattice gauge theories and of models with bosonic modes; the gate complexity depends almost linearly on spacetime volume in the former case, and almost quadratically on time in the latter case. We establish a lower bound showing that there are systems involving bosons for which this quadratic scaling with time cannot be improved. By applying our result on the truncation error in time evolution, we also prove that spectrally isolated energy eigenstates can be approximated with accuracy ϵ by truncating local quantum numbers at Λ = polylog(ϵ⁻¹)
Paleogeographic Reconstructions of an Ocean Margin on Mars Based on Deltaic Sedimentology at Aeolis Dorsa
No full textThe evidence for an ancient ocean in Mars' northern hemispheric basin during the Noachian/Hesperian is contentious. Much of the work is based on the modern topography by assuming that erosion has not significantly reshaped the Martian surface over the last 3.5 billion years, despite evidence to the contrary. Here, we provide new evidence for a northern ocean or large sea based on stratigraphic analysis of sedimentary basin fill exposed at Aeolis Dorsa. We mapped over 6,500 km of fluvial ridges, grouped them into 20 systems, and present evidence that they are the eroded remnants of river deltas or submarine-channel belts, together defining the stratigraphy of an ancient ocean margin. We used Context Camera stereo-pair elevation models to measure the stratigraphic positions of each system and used branching directions to determine paleoflow directions. By grouping landforms based on stratigraphic position and paleoflow directions, we reconstructed the paleogeography at Aeolis Dorsa over 5 timesteps; all cases differ from the modern topography. We tracked the initial regression and later transgression of a shoreline during at least 900 m of sea-level rise, a scale consistent with a northern ocean on a warm and wet early Mars
Mineralogy and geochemistry of serpentinized peridotites of the Northern Nubian Shield: The origin of compositionally banded olivine and implications for Neoproterozoic supra-subduction zone metasomatism
No full textA sequence of Neoproterozoic ultramafic rocks — serpentinized peridotite, serpentinite, and clinopyroxenite — outcrop in Wadi El-Mireiwa in the south Eastern Desert of Egypt. They represent the mantle and lowermost crustal section of a fragmented ophiolite, emplaced by thrusting above metasedimentary rocks and an island arc assemblage and later intruded by a granite mass. In samples of the serpentinized peridotite, back-scattered electron images of olivine reveal banded zoning, defined by straight and parallel Mg-enriched (Fo ∼ 96) lamellae within typically magnesian host crystals (Fo ∼ 89). The presence of clinopyroxene, the relatively low whole-rock Mg# (∼88), the low NiO content of olivine (0.1–0.32 wt%), and the relatively high TiO₂ content of fresh Cr-spinel (∼0.3 wt%) are all consistent with a cumulate origin for the serpentinized peridotite and serpentinites. On the other hand, some associated serpentinite has higher whole-rock Mg# (92) and low TiO₂ in Cr-spinel (∼0.01 wt%), consistent with a residual origin by high-degree melt extraction in the fore-arc region of a supra-subduction zone (SSZ) environment. The formation of Mg-enriched bands in olivine is attributed to the enhancement of metasomatic Mg-Fe exchange with high-Mg/Fe²⁺ fluids along crystallographically-oriented subgrain boundaries produced by high strain-rate dislocation creep. Such high-Mg/Fe²⁺ fluid metasomatism also explains reverse zoning of MgO in Cr-spinel, whereas the low whole-rock concentrations of REE and other trace elements exclude a significant role for melt-rock interaction. The evidence for high-Mg/Fe²⁺ fluid metasomatism in this suite indicates that SSZ fluids and high fore-arc strain rates affect not only the mantle wedge but also overlying ultramafic cumulates. The oxygen fugacity [ΔlogƒO₂(FMQ)] values calculated from unmetasomatized (+2.48 to +2.67) and metasomatized (+3.75 to +4.53) samples reflect the oxidized nature of Neoproterozoic SSZ magma and the even more oxidizing character of the metasomatic fluids. Banded zoning has also been recorded in olivine from Mariana fore-arc peridotite and Phanerozoic SSZ ophiolites; the Neoproterozoic Wadi El-Mireiwa case shows that rapid mantle flow has been a persistent feature of the tectonic environment where fore-arc ophiolites develop
Observations of 4U 1626–67 with the Imaging X-Ray Polarimetry Explorer
No full textWe present measurements of the polarization of X-rays in the 2–8 keV band from the pulsar in the ultracompact low-mass X-ray binary 4U 1626–67 using data from the Imaging X-Ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were clearly detected throughout the IXPE observations as well as in the NICER soft X-ray observations, which we used as the basis for our timing analysis and to constrain the spectral shape over the 0.4–10 keV energy band. Chandra HETGS high-resolution X-ray spectra were also obtained near the times of the IXPE observations for firm spectral modeling. We found an upper limit on the pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there was no significant detection of polarized flux in pulse phase intervals when subdividing the bandpass by energy. However, spectropolarimetric modeling over the full bandpass in pulse phase intervals provided a marginal detection of polarization of the power-law spectral component at the 4.8% ± 2.3% level (90% confidence). We discuss the implications concerning the accretion geometry onto the pulsar, favoring two-component models of the pulsed emission
Expressive power of complex-valued restricted Boltzmann machines for solving nonstoquastic Hamiltonians
No full textVariational Monte Carlo with neural network quantum states has proven to be a promising avenue for evaluating the ground-state energy of spin Hamiltonians. However, despite continuous efforts the performance of the method on frustrated Hamiltonians remains significantly worse than those on stoquastic Hamiltonians that are sign free. We present a detailed and systematic study of restricted Boltzmann machine (RBM) based variational Monte Carlo for quantum spin chains, resolving how relevant stoquasticity is in this setting. We show that in most cases, when the Hamiltonian is phase connected with a stoquastic point, the complex RBM state can faithfully represent the ground state, and local quantities can be evaluated efficiently by sampling. On the other hand, we identify several new phases that are challenging for the RBM Ansatz, including nontopological robust nonstoquastic phases as well as stoquastic phases where sampling is nevertheless inefficient. We further find that, in contrast to the common belief, an accurate neural network representation of ground states in nonstoquastic phases is hindered not only by the sign structure but also by their amplitudes
Using Preference Estimates to Customize Incentives: An Application to Polio Vaccination Drives in Pakistan
No full textWe use estimates of time preferences to customize incentives for polio vaccinators in Lahore, Pakistan. We measure time preferences using intertemporal allocations of effort, and use these estimates to construct individually tailored incentives. We evaluate the effect of matching contract terms to discounting parameters in a subsequent experiment with the same vaccinators. Our tailored policy is compared with alternatives that either rely on atheoretic reduced-form relationships for policy guidance or apply the same policy to all individuals. We find that contracts tailored to individual discounting outperform this range of policy alternatives