Direct Constraints Research Articles

Resolving muon g-2 anomaly with partial compositeness

We consider the scenario of composite Higgs with partial compositeness to address the muon g-2 anomaly. We show that this anomaly is resolved by one-loop correction due to composite muon partners with mass scale of order TeVs and large Yukawa coupling to composite Higgs, which is different from interpretations of vectorlike lepton models. We present parameter space by imposing indirect constraints from precise measurements on Higgs, Z and oblique electroweak parameters. We analyze direct constraints in light of both Drell–Yan and Higgs-associated productions of the composite muon partners at high-luminosity LHC. It turns out that the parameter regions with the lighter composite muon mass below sim 325 GeV can be excluded at 2sigma order by the Drell–Yan processes.

Surface waves and crustal structure on Mars.

We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.

Anti-weaponization of Outer Space for Maintaining Long-term Sustainability of Outer Space Activities

Space weaponization should be prevented because of its detrimental effects on the long-term sustainability of outer space activities (LTSOSA). International law that currently governs weaponization in outer space should be implemented, and international rules that pertain to the LTSOSA should impose direct and indirect soft-law constraints on space weaponization. Nevertheless, the direct and indirect roles of international law in inhibiting space weaponization are limited, and a legal lacuna still exists in the governance of conventional weapons in the Earth's orbit. Independent and more focused discussions on specific issues related to space security are recommended given that the disagreement on related issues has prevented real progress from being made during multilateral discussions addressing the space technologies that could be used in a hostile manner. The integration of some norms of responsible space activity into the new LTSOSA Guidelines discussed under the auspices of the United Nations Committee on the Peaceful Uses of Outer Space is also recommended, along with an ongoing strong political constraint on the deployment and testing of dedicated space weapons in outer space through the adoption of the United Nations General Assembly resolutions and international condemnation. The latter is a good alternative under the current circumstances to preserve the LTSOSA by working against the weaponization of outer space.

Spacecraft orbital pursuit–evasion games with [formula omitted] perturbations and direction-constrained thrust

In this paper, we study spacecraft orbital pursuit–evasion games under J2 perturbations. We consider that situation where the thrust of each player is constrained and the control direction cannot deviate from the velocity more than a given angle. After characterizing the optimal control of players under direction constraints, we transfer the pursuit–evasion game into a two point boundary value problem, which is solved by the shooting method. Different with the classical research, the initial guess for the unknown initial adjoint variables and the game ending time are not generated by heuristic approaches, but from the solution of the orbital one-side interception problem with a non-maneuverable evader. We solve the one-side interception problem also by shooting, starting iteratively from multiple initial guesses. In each initial guess, the initial adjoint vector is chosen randomly small while the interception termination time is selected from contiguous feasible time subintervals. The simulations show that the shooting method for the one-side interception problem can converge even if the feasible interval of the termination time is partitioned into a small number of subintervals, and the whole method for solving the pursuit–evasion game can quickly find the saddle-point solution. The effect of the control direction constraint on the game ending time is also discussed.

Signature of a light charged Higgs boson from top quark pairs at the LHC

The charged Higgs boson is a smoking gun of extensions of the standard model with multiple Higgs doublets, and has been searched for at various collider experiments. In this paper, we study the signature of a light charged Higgs boson produced by top quark pairs at the Large Hadron Collider (LHC), with subsequent three-body decays into a $W$ boson and a pair of bottom quarks. Cross sections on final states of two $W$ bosons plus four bottom quarks have been measured by the ATLAS Collaboration at the LHC 13 TeV. We reinterpret the experimental data under the scenario of a light charged Higgs boson and find improved agreements. We obtain the first limit from LHC direct searches on the total branching ratio of the three-body decay, $\mathrm{Br}(t\ensuremath{\rightarrow}{H}^{+}b)\ifmmode\times\else\texttimes\fi{}\mathrm{Br}({H}^{+}\ensuremath{\rightarrow}{W}^{+}b\overline{b})$, and the strongest direct constraints on the parameter space of a class of type-I two-Higgs-doublet models.

The whisper of a whimper of a bang: 2400 d of the Type Ia SN 2011fe reveals the decay of 55Fe

ABSTRACT We analyse new multifilter Hubble Space Telescope (HST) photometry of the normal Type Ia supernova (SN Ia) 2011fe out to ≈2400 d after maximum light, the latest observations to date of a SN Ia. We model the pseudo-bolometric light curve with a simple radioactive decay model and find energy input from both 57Co and 55Fe are needed to power the late-time luminosity. This is the first detection of 55Fe in a SN Ia. We consider potential sources of contamination such as a surviving companion star or delaying the deposition time-scale for 56Co positrons but these scenarios are ultimately disfavored. The relative isotopic abundances place direct constraints on the burning conditions experienced by the white dwarf (WD). Additionally, we place a conservative upper limit of <10−3 M⊙ on the synthesized mass of 44Ti. Only two classes of explosion models are currently consistent with all observations of SN 2011fe: (1) the delayed detonation of a low-ρc, near-MCh (1.2–1.3 M⊙) WD, or (2) a sub-MCh (1.0–1.1 M⊙) WD experiencing a thin-shell double detonation.

Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Γinit below the Γinit ∼ 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g − r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day−1), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a γ-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three “orphan” events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in γ-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing γ-rays and the material producing early optical afterglow emission, finding that they must be comparable.

The Geometry of Optimal Gaits for Inertia-Dominated Kinematic Systems

Isolated mechanical systems—e.g., those floating in space, in free-fall, or on a frictionless surface—are able to achieve net rotation by cyclically changing their shape, even if they have no net angular momentum. Similarly, swimmers immersed in “perfect fluids” are able to use cyclic shape changes to both translate and rotate even if the swimmer-fluid system has no net linear or angular momentum. Finally, systems fully constrained by direct nonholonomic constraints (e.g., passive wheels) can push against these constraints to move through the world. Previous work has demonstrated that the displacement induced by these shape changes corresponds to the amount of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">constraint curvature</i> that the gaits enclose. Properly assessing or optimizing the utility of a gait also requires considering the time or resources required to execute it: A gait that produces a small displacement per cycle, but that can be executed in a short time, may produce a faster average velocity than a gait that produces more displacement, but takes longer to complete a cycle at the same instantaneous effort. In this paper, we consider gaits under two instantaneous measures of effort. For each of these costs, we demonstrate that fixing the average instantaneous cost to a unit value allows us to transform the effort costs into time-to-execute costs for any given gait cycle. We then illustrate how the interaction between the constraint curvature and these costs leads to characteristic geometries for optimal cycles, in which the gait trajectories resemble elastic hoops distended from within by internal pressures.

Probing the Upper End of Intracontinental Earthquake Magnitude: A Prehistoric Example From the Dzhungarian and Lepsy Faults of Kazakhstan

AbstractThe study of surface ruptures is key to understanding the earthquake occurrence of faults especially in the absence of historical events. We present a detailed analysis of geomorphic displacements along the Dzhungarian Fault, which straddles the border of China and Kazakhstan. We use digital elevation models derived from structure‐from‐motion analysis of Pléiades satellite imagery and drone imagery from specific field sites to measure surface offsets. We provide direct age constraints from alluvial terraces displaced by faulting and indirect dating from morphological analysis of the scarps. We find that the southern 250 km of the fault likely ruptured in a single event in the last 4,000 years, with displacements of 10–15 m, and potentially up to 20 m at one site. We infer that this Dzhungarian rupture is likely linked with a previously identified paleo‐earthquake rupture on the Lepsy Fault through a system of splays in the intervening highlands. Though there are remaining uncertainties regarding consistency in age constraints between the two fault ruptures, most of the sites along the two faults are consistent with a most recent event 2,000–4,000 years ago. Rupture on the Dzhungarian Fault alone is likely to have exceeded Mw 8, and the combined Lepsy‐Dzhungarian rupture scenario may have been up to Mw 8.4. Despite being at the upper end of known or inferred continental earthquake magnitudes, our proposed scenario combining the 375 km of the Dzhungarian and Lepsy ruptures yields a slip‐to‐length ratio consistent with global averages and so do other historical intracontinental earthquakes in Central Asia.

Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b

Context. High-resolution spectroscopy studies of ultra-hot Jupiters have been key in our understanding of exoplanet atmospheres. Observing into the atmospheres of these giant planets allows for direct constraints on their atmospheric compositions and dynamics while laying the groundwork for new research regarding their formation and evolution environments. Aims. Two of the most well-studied ultra-hot Jupiters are WASP-76b and WASP-121b, with multiple detected chemical species and strong signatures of their atmospheric dynamics. We take a new look at these two exceptional ultra-hot Jupiters by reanalyzing the transit observations taken with ESPRESSO at the Very Large Telescope and attempt to detect additional species. Methods. To extract the planetary spectra of the two targets, we corrected for the telluric absorption and removed the stellar spectrum contributions. We then exploited new synthetic templates that were specifically designed for ultra-hot Jupiters in combination with the cross-correlation technique to unveil species that remained undetected by previous analyses. Results. We add a novel detection of Ba+ to the known atmospheric compositions of WASP-76b and WASP-121b, the heaviest species detected to date in any exoplanetary atmosphere, with additional new detections of Co and Sr+ and a tentative detection of Ti+ for WASP-121b. We also confirm the presence of Ca+, Cr, Fe, H, Li, Mg, Mn, Na, and V on both WASP-76b and WASP-121b, with the addition of Ca, Fe+, and Ni for the latter. Finally, we also confirm the clear asymmetric absorption feature of Ca+ on WASP-121b, with an excess absorption at the bluer wavelengths and an effective planet radius beyond the Roche lobe. This indicates that the signal may arise from the escape of planetary atmosphere.

Speculations on the W-mass measurement at CDF* *J.G. is supported by the National Natural Science Foundation of China (NNSFC) ( 12035008). Z.L. is supported in part by the U.S. Department of Energy (DOE) (DE-SC0022345). T.M. is supported by "Study in Israel" Fellowship for Outstanding Post-Doctoral Researchers from China, by PBC of CHE from India, and also partially supported by grants

The W mass determination at the Tevatron CDF experiment reported a deviation from the SM expectation at the 7σ level. We discuss a few possible interpretations and their collider implications. We perform electroweak global fits under various frameworks and assumptions. We consider three types of electroweak global fits in the effective-field-theory framework: the S-T, S-T-, and eight-parameter flavor-universal one. We discuss the amounts of tensions between different measurements reflected in these fits and the corresponding shifts in central values of these parameters. With these electroweak fit pictures in hand, we present a few different classes of models and discuss their compatibility with these results. We find that while explaining the discrepancy, the single gauge boson extensions face strong LHC direct search constraints unless the is fermiophobic (leptophobic), which can be realized if extra vector fermions (leptons) mix with the SM fermions (leptons). Vector-like top partners can partially generate the needed shift to the electroweak observables. The compatibility with the top squark is also studied in detail. We find that the non-degenerate top squark soft masses enhance the needed operator coefficients, enabling an allowed explanation compatible with current LHC measurements. Overall, more theoretical and experimental developments are highly in demand to reveal the physics behind this discrepancy.

Perspective on satellite-based land data assimilation to estimate water cycle components in an era of advanced data availability and model sophistication

The beginning of the 21st century is marked by a rapid growth of land surface satellite data and model sophistication. This offers new opportunities to estimate multiple components of the water cycle via satellite-based land data assimilation (DA) across multiple scales. By resolving more processes in land surface models and by coupling the land, the atmosphere, and other Earth system compartments, the observed information can be propagated to constrain additional unobserved variables. Furthermore, access to more satellite observations enables the direct constraint of more and more components of the water cycle that are of interest to end users. However, the finer level of detail in models and data is also often accompanied by an increase in dimensions, with more state variables, parameters, or boundary conditions to estimate, and more observations to assimilate. This requires advanced DA methods and efficient solutions. One solution is to target specific observations for assimilation based on a sensitivity study or coupling strength analysis, because not all observations are equally effective in improving subsequent forecasts of hydrological variables, weather, agricultural production, or hazards through DA. This paper offers a perspective on current and future land DA development, and suggestions to optimally exploit advances in observing and modeling systems.

Complementing XCO2 imagery with ground-based CO2 and 14CO2 measurements to monitor CO2 emissions from fossil fuels on a regional to local scale

Abstract. Various satellite imagers of the vertically integrated column of carbon dioxide (XCO2) are under development to enhance the capabilities for the monitoring of fossil fuel (FF) CO2 emissions. XCO2 images can be used to detect plumes from cities and large industrial plants and to quantify the corresponding emission using atmospheric inversions techniques. However, this potential and the ability to catch the signal from more diffuse FF CO2 sources can be hampered by the mix between these FF signals and a background signal from other types of CO2 surface fluxes, and in particular of biogenic CO2 fluxes. The deployment of dense ground-based air-sampling networks for CO2 and radiocarbon (14CO2) could complement the spaceborne imagery by supporting the separation between the fossil fuel and biogenic or biofuel (BF) CO2 signals. We evaluate this potential complementarity with a high-resolution analytical inversion system focused on northern France, western Germany, Belgium, Luxembourg, and a part of the Netherlands and with pseudo-data experiments. The inversion system controls the FF and BF emissions from the large urban areas and plants, in addition to regional budgets of more diffuse emissions or of biogenic fluxes (NEE, net ecosystem exchange), at an hourly scale over a whole day. The system provides results corresponding to the assimilation of pseudo-data from a single track of a 300 km swath XCO2 imager at 2 km resolution and from surface ground-based CO2 and/or 14CO2 networks. It represents the diversity of 14CO2 sources and sinks and not just the dilution of radiocarbon-free FF CO2 emissions. The uncertainty in the resulting FF CO2 emissions at local (urban area/plant) to regional scales is directly derived and used to assess the potential of the different combinations of observation systems. The assimilation of satellite observations yields estimates of the morning regional emissions with an uncertainty down to 10 % (1σ) in the satellite field of view, from an assumed uncertainty of 15 % in the prior estimates. However, it does not provide direct information about emissions outside the satellite field of view or about afternoon or nighttime emissions. The co-assimilation of 14CO2 and CO2 surface observations leads to a further reduction of the uncertainty in the estimates of FF emissions. However, this further reduction is significant only in administrative regions with three or more 14CO2 and CO2 sampling sites. The uncertainty in the estimates of 1 d emission in North Rhine-Westphalia, a region with three sampling sites, decreases from 8 % to 6.6 % when assimilating the in situ 14CO2 and CO2 data in addition to the satellite data. Furthermore, this additional decrease appears to be larger when the ground stations are close to large FF emission areas, providing an additional direct constraint for the estimate of these sources rather than supporting the characterization of the background signal from the NEE and its separation from that of the FF emissions. More generally, the results indicate no amplification of the potential of each observation subsystem when they are combined into a large observation system with satellite and surface data.

The use of a semi‐structured finite‐element mesh in 3‐D resistivity inversion

AbstractCalculating the electric potential for 3‐D resistivity inversion algorithms can be time consuming depending on the structure of the mesh. There have been generally two approaches to generating finite‐element meshes. One approach uses a structured rectangular mesh with hexahedral elements on a rectangular model grid. The distribution of model cells can be designed to follow known boundaries, and directional roughness constraints can be easily imposed. A 1‐D wavelet transform that takes advantage of the regular arrangement of the model cells can also be used to reduce the computer time and memory required to solve the smoothness‐constrained least‐squares equation. However, the structured rectangular mesh uses an unnecessarily fine mesh in parts of the model that are far away from the electrodes where the potential changes gradually. A second approach uses an unstructured mesh with tetrahedral elements created automatically by a mesh generation program with finer elements nearer the electrodes and coarser elements in the more remote regions. This generates a mesh with a much smaller number of nodes. The disadvantage is that an irregular model grid is normally used. We examine an alternative approach that combines structured and unstructured meshes. We employ a regular model grid with a finer mesh near the surface and a coarser mesh in deeper regions using a combination of hexahedral and tetrahedral elements. The semi‐structured mesh reduces the calculation time by more than three times compared with a structured mesh. An adaptive semi‐structured mesh that also uses a coarser mesh for model cells near the surface if they are more than one unit electrode spacing from the nearest electrode was also developed for surveys with non‐uniform data coverage. For the Bonsall Leys field survey, which used a capacitively coupled mobile system and collected a data set with nearly a million electrode positions, the adaptive mesh reduces the calculation time by about 80%. The calculation time can be further reduced by about 93% when it is combined with a mesh segmentation method.

Calculating Co-Seismic Three-Dimensional Displacements from InSAR Observations with the Dislocation Model-Based Displacement Direction Constraint: Application to the 23 July 2020 Mw6.3 Nima Earthquake, China

As one of the most prevailing geodetic tools, the interferometric synthetic aperture radar (InSAR) technique can accurately obtain co-seismic displacements, but is limited to the one-dimensional line-of-sight (LOS) measurement. It is therefore difficult to completely reveal the real three-dimensional (3D) surface displacements with InSAR. By employing azimuth displacement observations from pixel offset tracking (POT) and multiple aperture InSAR (MAI) techniques, 3D displacements of large-magnitude earthquakes can be obtained by integrating the ascending and descending data. However, this method cannot be used to accurately realize the 3D surface displacement measurements of small-magnitude earthquakes due to the low accuracies of the POT/MAI-derived azimuth displacement measurements. In this paper, an alternative method is proposed to calculate co-seismic 3D displacements from ascending and descending InSAR-LOS observations with the dislocation model-based displacement direction constraint. The main contribution lies in the two virtual observation equations that are obtained from the dislocation model-based forward-modeling 3D displacements, which are then combined with the ascending/descending InSAR observations to calculate the 3D displacements. The basis of the two virtual observation equations is that the directions of the 3D displacement vectors are very similar for real and model-based 3D displacements. In addition, the weighted least squares (WLS) method is employed to solve the final 3D displacements, which aims to consider and balance the possible errors in the InSAR observations as well as the dislocation model-based displacement direction constraint. A simulation experiment demonstrates that the proposed method can achieve more accurate 3D displacements compared with the existing methods. The co-seismic 3D displacements of the 2020 Nima earthquake are then accurately obtained by the proposed method. The results show that co-seismic displacements are dominated by the vertical displacement, the magnitude of the horizontal displacement is relatively small, and the overall displacement pattern fits well with the tensile rupture.

Direct constraints on in situ stress state from deep drilling into the Nankai subduction zone, Japan

Abstract Stress state is a long-sought but poorly known parameter on subduction megathrusts and in overlying accretionary wedges in general. We used direct observations made during drilling of Integrated Ocean Drilling Program (IODP) borehole C0002 to a depth of 3058 m below the seafloor (mbsf) in the Nankai subduction zone of southwestern Japan to constrain in situ pore pressure and stress state in the deep interior of an accretionary wedge for the first time. These data included downhole pressure, active pumping tests, and logging and sample measurements. We found a nearly linear gradient in minimum horizontal principal stress (Shmin) and show that it remained consistently smaller than the vertical stress (Sv), definitively ruling out a thrust-faulting stress regime to at least 3 km depth, and to within ~2 km above the subduction megathrust. At 3000 mbsf, the estimated effective stresses were: Sv = 33 MPa, SHmax = 25–36 MPa, and Shmin = 18.5–21 MPa. We therefore interpret that the stress state throughout the drilled interval, which lies entirely in the hanging wall of the active megathrust, lies in a normal or strike-slip faulting regime (Sv ≥ SHmax &amp;gt; Shmin). Total differential stresses are below ~18 MPa. We conclude that (1) basal traction along the megathrust must be small in order to permit both locking (and frictional sliding at failure) of the décollement and such low differential stresses deep within the upper plate; and (2) although differential stresses may remain low all the way to the plate boundary at ~5000 mbsf, SHmax must transition to become greater than the vertical stress—either spatially below the base of the borehole or temporally leading up to megathrust fault rupture—in order to drive thrust motion along the plate boundary as observed in great earthquakes and in recurring very low-frequency earthquakes and slow-slip events.

Discovery of Line Pressure Broadening and Direct Constraint on Gas Surface Density in a Protoplanetary Disk

The gas surface density profile of protoplanetary disks is one of the most fundamental physical properties to understanding planet formation. However, it is challenging to determine the surface density profile observationally, because the H2 emission cannot be observed in low-temperature regions. We analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) archival data of the 12CO J = 3 − 2 line toward the protoplanetary disk around TW Hya and discovered extremely broad line wings due to the pressure broadening. In conjunction with a previously reported optically thin CO isotopologue line, the pressure broadened line wings enabled us to directly determine the midplane gas density for the first time. The gas surface density at ∼5 au from the central star reaches ∼103 g cm−2, which suggests that the inner region of the disk has enough mass to form a Jupiter-mass planet. Additionally, the gas surface density drops at the inner cavity by ∼2 orders of magnitude compared to outside the cavity. We also found a low CO abundance of ∼10−6 with respect to H2, even inside the CO snow line, which suggests conversion of CO to less volatile species. Combining our results with previous studies, the gas surface density jumps at r ∼ 20 au, suggesting that the inner region (3 < r < 20 au) might be the magnetorotational instability dead zone. This study sheds light on the direct gas surface density constraint without assuming the CO/H2 ratio using ALMA.

Sulfur in apatite from the Nakhla meteorite record a late-stage oxidation event

Estimates of the oxygen fugacity (fO2) recorded by the Martian nakhlite meteorites from direct observations of the main igneous phenocryst assemblages range from values similar to that recorded by the quartz-fayalite-magnetite oxygen buffer to ∼two orders of magnitude lower. Inferences of changes in fO2 during the late stages of crystallization, volcanic degassing, and emplacement of the nakhlite cumulate pile have been made based on variable sulfide and apatite chemistry. We present S-XANES measurements of the oxidation state of sulfur in apatite and associated mesostasis glass in Nakhla to place direct constraints on the magnitude of changes in fO2 experienced by the Nakhla portion of the nakhlite cumulate pile during apatite crystallization. Nakhla apatites range from containing dominantly S2− to containing dominantly S6+. This, together with correlations between S2−, Cl, and FeO in the mesostasis glass near these apatites, suggest that our measurements capture directly the oxidation of the interstitial late-stage Nakhla magmas as the result of Cl-saturation and degassing. As the result of this degassing, at least part of the nakhlite cumulate pile experienced an increase in fO2 of ∼1.5–2.5 orders of magnitude during apatite crystallization and final mesostasis cooling. Based on these measurements, the sulfur oxidation states of apatites in the other nakhlite meteorites are predicted to range from exclusively S2−-bearing to exclusively S6+-bearing.

A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs

The spectra of brown dwarfs are key to exploring the chemistry and physics that take place in their atmospheres. Late-T dwarf spectra are particularly diagnostic, due to their relatively cloud-free atmospheres and deep molecular bands. With the use of powerful atmospheric retrieval tools applied to the spectra of these objects, direct constraints on molecular/atomic abundances, gravity, and vertical thermal profiles can be obtained, enabling a broad exploration of the chemical/physical mechanisms operating in their atmospheres. We present a uniform retrieval analysis on low-resolution Infrared Telescope Facility SpeX near-infrared spectra for a sample of 50 T dwarfs, including new observations as part of a recent volume-limited survey. This analysis more than quadruples the sample of T dwarfs with retrieved temperature profiles and abundances (H2O, CH4, NH3, K, and subsequent C/O and metallicities). We are generally able to constrain the effective temperatures to within 50 K, the volume mixing ratios for major species to within 0.25 dex, the atmospheric metallicities [M/H] to within 0.2, and the C/O ratios to within 0.2. We compare our retrieved constraints on the thermal structures, chemistry, and gravities of these objects with predictions from self-consistent radiative-convective equilibrium models and find, in general, though with substantial scatter, consistency with solar composition chemistry and the thermal profiles of the neighboring stellar FGK population. Objects with notable discrepancies between the two modeling techniques and potential mechanisms for their differences, be they related to the modeling approach or physically motivated, are discussed more thoroughly in the text.

Illite K-Ar and (U-Th)/He low-temperature thermochronology reveal onset timing of Yadong-Gulu rift in southern Tibetan Plateau

Determining the timing of E-W extension across the NS-trending rifts in southern Tibet is key to test the mechanical models of the latest evolution in the collision between India and Asia. We focus on the southern half of the largest of the seven main rifts, the Yadong-Gulu rift (YGR), which, despite being the focus of numerous studies thanks to its easy access, still lacks direct time constraints. Using illite K-Ar ages of fault gouge from the active Yadong normal fault of the YGR, we directly constrain its onset timing at 9 ± 1 Ma. (U-Th)/He dating of the footwall leucogranite reveals a rapid exhumation of the southern YGR since ∼9 Ma, attesting to its onset activity. Such timing is similar to that estimated for the northern half of the YGR at 8 ± 1 Ma, suggesting that the entire YGR formed at approximately the same time. Our synthesis of published initiation ages of the other main rifts in southern Tibet shows that they mostly fall between ∼23 and 8 Ma, suggesting a clear spatial and temporal pattern of old initiation ages to the west and young to the east. In this case, the formation of rifts in southern Tibet is unlikely caused by slab tearing of the underthruting Indian plate or orogenic collapse. Our study supports that E-W extension in Tibetan Plateau is triggered by a combination of eastward propagation of the Karakorum-Jiali fault zone and divergent thrusting along the curved Himalayan arc.