ShantanuT01/DACTYL-Pretraining huggingface dataset:
We report 4 new pulsars discovered in the core-collapsed globular cluster (GC) NGC 6624 by the TRAPUM Large Survey Project with the MeerKAT telescope. All of the new pulsars found are isolated. PSR J1823$-$3021I and PSR J1823$-$3021K are millisecond pulsars with period of respectively 4.319 ms and 2.768 ms. PSR J1823$-$3021J is mildly recycled with a period of 20.899 ms, and PSR J1823$-$3022 is a long period pulsar with a period of 2.497 s. The pulsars J1823$-$3021I, J1823$-$3021J, and J1823$-$3021K have position and dispersion measure (DM) compatible with being members of the GC and are therefore associated with NGC 6624. Pulsar J1823$-$3022 is the only pulsar bright enough to be re-detected in archival observations of the cluster. This allowed the determination of a timing solution that spans over two decades. It is not possible at the moment to claim the association of pulsar J1823$-$3022 with the GC given the long period and large offset in position ($\sim 3$ arcminutes) and DM (with a fractional difference of 11 percent compared the average of the pulsars in NGC 6624). The discoveries made use of the beamforming capability of the TRAPUM backend to generate multiple beams in the same field of view which allows sensitive searches to be performed over a few half-light radii from the cluster center and can simultaneously localise the discoveries. The discoveries reflect the properties expected for pulsars in core-collapsed GCs.
In this paper we study the ergodicity properties of some adaptive Markov chain Monte Carlo algorithms (MCMC) that have been recently proposed in the literature. We prove that under a set of verifiable conditions, ergodic averages calculated from the output of a so-called adaptive MCMC sampler converge to the required value and can even, under more stringent assumptions, satisfy a central limit theorem. We prove that the conditions required are satisfied for the independent Metropolis--Hastings algorithm and the random walk Metropolis algorithm with symmetric increments. Finally, we propose an application of these results to the case where the proposal distribution of the Metropolis--Hastings update is a mixture of distributions from a curved exponential family.
Let $a\in (0,\infty)$. For a spectrally negative L\'evy process $X$ with infinite variation paths the resolvent of the process killed on hitting the two-point set $V=\{-a,a\}$ is identified. When further $X$ has no diffusion component the Laplace transforms of the entrance laws of the excursion measures of $X$ from $V$ are determined. This is then applied to establishing the Laplace transform of the amount of time that elapses between the last visit of $X$ to a given point $x$, before hitting some other point $y>x$, and the hitting time of $y$. All the expressions are explicit and tractable in the standard fluctuation quantities associated to $X$.
A method for obtaining the small current quark mass effect on the dressed quark propagator from an effective quark-quark interaction model is developed. Within this approach both explicit and dynamical chiral symmetry breaking has been analyzed. a comparision with previous results is given.
We investigate the quenching process in lattice systems with short range interaction and several crystalline states as ground states. We consider in particular the following systems on square lattice:   - hard particle (exclusion) model;   - q states planar Potts model.   The system is initially in a homogeneous disordered phase and relaxes toward a new equilibrium state as soon as the temperature is rapidly lowered. The time evolution can be described numerically by a stochastic process such as the Metropolis algorithm. The number of pure, equivalent, ground states is q for the Potts model and r for the hard particle model, and it is known that for r or q larger or equal to d+1, the final equilibrium state may be polycrystalline, i.e. not made of a uniform phase. We find that in addition n_g and q_g exist such that for r > r_g, or q > q_g the system evolves toward a glassy state, i.e. a state in which the ratio of the interaction energy among the different crystalline phases to the total energy of the system never vanishes; moreover we find indications that r_g=q_g. We infer that q=q_g (and r=r_g) corresponds to the crossing from second order to discontinuous transition in the phase diagram of the system.
Recent statistical X-ray measurements of the intracluster medium (ICM) indicate that gas temperature profiles in the outskirts of galaxy clusters deviate from self-similar evolution. Using a mass-limited sample of galaxy clusters from cosmological hydrodynamical simulations, we show that the departure from self-similarity can be explained by non-thermal gas motions driven by mergers and accretion. Contrary to previous claims, gaseous substructures only play a minor role in the temperature evolution in cluster outskirts. A careful choice of halo overdensity definition in self-similar scaling mitigates these departures. Our work highlights the importance of non-thermal gas motions in ICM evolution and the use of galaxy clusters as cosmological probes.
Symmetries compatible with asymptotic flatness and admitting gravitational and electromagnetic radiation are studied by using the Bondi-Sachs-van der Burg formalism. It is shown that in axially symmetric electrovacuum spacetimes in which at least locally a smooth null infinity in the sense of Penrose exists, the only second allowable symmetry is either the translational symmetry or the boost symmetry. Translationally invariant spacetimes with in general a straight "cosmic string" along the axis of symmetry are non-radiative although they can have a non-vanishing news function. The boost-rotation symmetric spacetimes are radiative. They describe "uniformly accelerated charged particles" or black holes which in general may also be rotating - the axial and an additional Killing vector are not assumed to be hypersurface orthogonal. The general functional forms of both gravitational and electromagnetic news functions, and of the mass aspect and total mass of asymptotically flat boost-rotation symmetric spacetimes at null infinity are obtained. The expressions for the mass are new even in the case of vacuum boost-rotation symmetric spacetimes with hypersurface orthogonal Killing vectors. In Appendices some errors appearing in previous works are corrected.
High-temperature, high-dose, neutron irradiation of W results in the formation of Re-rich clusters at concentrations one order of magnitude lower than the thermodynamic solubility limit. These clusters may eventually transform into brittle W-Re intermetallic phases, which can lead to high levels of hardening and thermal conductivity losses. Standard theories of radiation enhanced diffusion and precipitation cannot explain the formation of these precipitates and so understanding the mechanism by which nonequilibrium clusters form under irradiation is crucial to predict materials degradation and devise mitigation strategies. Here we carry out a thermodynamic study of W-Re alloys and conduct kinetic Monte Carlo simulations of Re cluster formation in irradiated W-2Re alloys using a generalized Hamiltonian for crystals containing point defects parameterized entirely with electronic structure calculations. Our model incorporates recently-gained mechanistic information of mixed-interstitial solute transport, which is seen to control cluster nucleation and growth by forming quasi-spherical nuclei after an average incubation time of 20 s at 1800 K. These nuclei are seen to grow by attracting more mixed interstitials bringing solute atoms, which in turns attracts vacancies leading to recombination and solute agglomeration. The clusters grow to a maximum size of approximately 4-nm radius, and are not fully dense with Re, containing 50% or less near the center. Our simulations are in reasonable agreement with recent atom probe examinations of ion irradiated W-2Re systems at 773 K.
We present detailed numerical simulations of a laser phase stabilization scheme for LISA, where both lasers emitting along one arm are locked to each other. Including the standard secondary noises and spacecraft motions that approximately mimic LISA's orbit, we verify that very stable laser phases can be obtained, and that time delay interferometry can be used to remove the laser phase noise from measurements of gravitational wave strains. Most importantly, we show that this locking scheme can provide significant simplifications over LISA's baseline design in the implementation of time delay interferometry.
The purpose of this paper is to further investigate the solution space of self-similar spherically symmetric perfect-fluid models and gain deeper understanding of the physical aspects of these solutions. We achieve this by combining the state space description of the homothetic approach with the use of the physically interesting quantities arising in the comoving approach. We focus on three types of models. First, we consider models that are natural inhomogeneous generalizations of the Friedmann Universe; such models are asymptotically Friedmann in their past and evolve fluctuations in the energy density at later times. Second, we consider so-called quasi-static models. This class includes models that undergo self-similar gravitational collapse and is important for studying the formation of naked singularities. If naked singularities do form, they have profound implications for the predictability of general relativity as a theory. Third, we consider a new class of asymptotically Minkowski self-similar spacetimes, emphasizing that some of them are associated with the self-similar solutions associated with the critical behaviour observed in recent gravitational collapse calculations.
We survey the foundations for Donaldson-Thomas invariants for stable sheaves on algebraic threefolds with trivial canonical bundle, with emphasis on the case of abelian threefolds.
We find a new example of an asymptotically $AdS_5 \times S^5$ geometry which has an entanglement shadow: that is, a region of spacetime which no Ryu-Takayanagi minimal surface enters. Our example is a particular case of the supersymmetric LLM geometries. Our results illustrate how minimal surfaces, which holographically geometrize entanglement entropy, can fail to probe the whole of spacetime, posing a challenge for attempts to directly reconstruct holographic geometries from the entanglement entropies of the dual field theory. We also comment on the relation to previous investigations of minimal surfaces localised in the $S^5$ factor of AdS$_5 \times S^5$.
Recent X-ray observations show absorbing winds with velocities up to mildly-relativistic values of the order of ~0.1c in a limited sample of 6 broad-line radio galaxies. They are observed as blue-shifted Fe XXV-XXVI K-shell absorption lines, similarly to the ultra-fast outflows (UFOs) reported in Seyferts and quasars. In this work we extend the search for such Fe K absorption lines to a larger sample of 26 radio-loud AGNs observed with XMM-Newton and Suzaku. The sample is drawn from the Swift BAT 58-month catalog and blazars are excluded. X-ray bright FR II radio galaxies constitute the majority of the sources. Combining the results of this analysis with those in the literature we find that UFOs are detected in >27% of the sources. However, correcting for the number of spectra with insufficient signal-to-noise, we can estimate that the incidence of UFOs is this sample of radio-loud AGNs is likely in the range f=(50+/-20)%. A photo-ionization modeling of the absorption lines with XSTAR allows to estimate the distribution of their main parameters. The observed outflow velocities are broadly distributed between v_out<1,000 km s^-1 and v_out~0.4c, with mean and median values of v_out~0.133c and v_out~0.117c, respectively. The material is highly ionized, with an average ionization parameter of log\xi~4.5 erg s^-1 cm, and the column densities are larger than N_H > 10^22 cm^-2. Overall, these characteristics are consistent with the presence of complex accretion disk winds in a significant fraction of radio-loud AGNs and demonstrate that the presence of relativistic jets does not preclude the existence of winds, in accordance with several theoretical models.
The linearized stability of charged thin shell wormholes under spherically symmetric perturbations is analized. It is shown that the presence of a large value of charge provides stabilization to the system, in the sense that the constrains onto the equation of state are less severe than for non-charged wormholes.
We propose a floating tunable coupler that does not rely on direct qubit-qubit coupling capacitances to achieve the zero-coupling condition. We show that the polarity of the qubit-coupler couplings can be engineered to offset the otherwise constant qubit-qubit coupling and attain the zero-coupling condition when the coupler frequency is above or below the qubit frequencies. We experimentally demonstrate these two operating regimes of the tunable coupler by implementing symmetric and asymmetric configurations of the coupler's superconducting pads with respect to the qubits. Such a floating tunable coupler provides flexibility in designing large-scale quantum processors while reducing the always-on residual couplings.
We demonstrate the reduction of critical spin-transfer torque (STT) switching currents in Co-Fe-B/MgO based magnetic tunnel junctions (MTJ) with perpendicular magnetization anisotropy (PMA). The junctions yield tunnel magnetoresistance (TMR) ratios of up to 64% at 4 monolayer (ML) tunnel barrier thickness. In this paper, the reduction of the critical switching current density is studied. By optimizing the applied bias field during DC-STT measurements, ultra low critical switching current densities of less than 20 kA/cm$^2$, even down to 9 kA/cm$^2$, are found. With the reduced switching currents, our samples are ideal candidates for further experimental studies such as the theoretical predicted thermally driven spin-transfer torque effect.
We present the results of a complete leading-twist next-to-leading order (NLO) QCD analysis of the spacelike pion electromagnetic form factor at large momentum transfer Q. We have studied their dependence on the form of the pion distribution amplitude. For a given distribution amplitude, we have examined the sensitivity of the predictions to the choice of the renormalization and factorization scales. Theoretical uncertainty of the LO results related to the renormalization scale ambiguity has been significantly reduced by including the NLO corrections. Adopting the criteria according to which a NLO prediction is considered reliable if, both, the ratio of the NLO to LO contributions and the strong coupling constant are reasonably small, we find that reliable perturbative predictions for the pion electromagnetic form factor with all distribution amplitudes considered can already be made at a momentum transfer Q<10 GeV, with corrections to the LO results being typically of the order of ~ 20%. To check our predictions and to discriminate between the distribution amplitudes, it is necessary to obtain experimental data extending to higher values of Q.
Two-dimensional layered materials, such as transition metal dichalcogenides (TMDCs), are promising materials for future electronics owing to their unique electronic properties. With the presence of a band gap, atomically thin gate defined quantum dots (QDs) can be achieved on TMDCs. Here, standard semiconductor fabrication techniques are used to demonstrate quantum confined structures on WSe2 with tunnel barriers defined by electric fields, thereby eliminating the edge states induced by etching steps, which commonly appear in gapless graphene QDs. Over 40 consecutive Coulomb diamonds with a charging energy of approximately 2 meV were observed, showing the formation of a QD, which is consistent with the simulations. The size of the QD could be tuned over a factor of 2 by changing the voltages applied to the top gates. These results shed light on quantum nano-devices on TMDCs for further researches.
If the very rare $B_d^0 \to \mu^+\mu^-$ decay is enhanced to (3--4) $\times 10^{-10}$ level or higher, it can be discovered with existing 2011-2012 LHC data. It might then cast some doubt on the Higgs boson nature of the 126 GeV boson, since the likely explanation would be due to the fourth generation $t^\prime$ quark. There is a mild motivation from the known tension in $\sin2\beta/\phi_1$. If discovery is made before the 13 TeV run, then the $b \to d$ quadrangle (modulo $m_{t'}$) would suddenly fall into our lap. Continued pursuit in future runs can probe below $3 \times 10^{-10}$.
Star formation in the centers of galaxies is thought to yield massive stars with a possibly top-heavy stellar mass distribution. It is likely that magnetic fields play a crucial role in the distribution of stellar masses inside star-forming molecular clouds. In this context, we explore the effects of magnetic fields, with a typical field strength of 38 microG, such as in RCW 38, and a field strength of 135 microG, similar to NGC 2024 and the infrared dark cloud G28.34+0.06, on the initial mass function (IMF) near (< 10 pc) a 10^7 solar mass black hole. Using these conditions, we perform a series of numerical simulations with the hydrodynamical code FLASH to elucidate the impact of magnetic fields on the IMF and the star-formation efficiency (SFE) emerging from an 800 solar mass cloud. We find that the collapse of a gravitationally unstable molecular cloud is slowed down with increasing magnetic field strength and that stars form along the field lines. The total number of stars formed during the simulations increases by a factor of 1.5-2 with magnetic fields. The main component of the IMF has a lognormal shape, with its peak shifted to sub-solar (< 0.3 M_sun) masses in the presence of magnetic fields, due to a decrease in the accretion rates from the gas reservoir. In addition, we see a top-heavy, nearly flat IMF above ~2 solar masses, from regions that were supported by magnetic pressure until high masses are reached. We also consider the effects of X-ray irradiation if the central black hole is active. X-ray feedback inhibits the formation of sub-solar masses and decreases the SFEs even further. Thus, the second contribution is no longer visible. We conclude that magnetic fields potentially change the SFE and the IMF both in active and inactive galaxies, and need to be taken into account in such calculations.
Several no-go theorems showed the incompatibility between the locality assumption and quantum correlations obtained from maximally entangled spin states. We analyze these no-go theorems in the framework of Bohm's interpretation. The mechanism by which non-local correlations appear during the results of measurements performed on distant parts of entangled systems is explicitly put into evidence in terms of Bohmian trajectories. It is shown that a GHZ like contradiction of the type+1=-1 occurs for well-chosen initial positions of the Bohmian trajectories and that it is this essential non-classical feature that makes it possible to violate the locality condition.
We investigate the orientation of the photospheric magnetic fields in the solar polar region using observations from the Helioseismic and Magnetic Imager (HMI). Inside small patches of significant polarization, the inferred magnetic field vectors at $1''$ scale appear to systematically deviate from the radial direction. Most tilt towards the pole; all are more inclined toward the plane of sky compared to the radial vector. These results, however, depend on the "filling factor" $f$ that characterizes the unresolved magnetic structures. The default, uninformative $f\equiv1$ for HMI will incur larger inclination and less radial fields than $f<1$. The observed trend may be a systematic bias inherent to the limited resolution.
Quantum computers, which take advantage of the superposition and entanglement of physical states, could outperform their classical counterparts in solving problems with technological impact, such as factoring large numbers and searching databases. A quantum processor executes algorithms by applying a programmable sequence of gates to an initialized state of qubits, which coherently evolves into a final state containing the result of the computation. Although quantum processors with a few qubits have been demonstrated on multiple quantum computing platforms, realization of solid-state programmable quantum processor under ambient conditions remains elusive. Here we report a programable quantum processor that can be programmed with fifteen parameters to realize arbitrary unitary transformations on two spin-qubits in a nitrogen-vacancy (NV) center in diamond. We implemented the Deutsch-Jozsa and Grover search algorithms with average success rates above 80\%. This programmable two-qubit processor could form a core component of a large-scale quantum processor, and the methods used here are suitable for such a device.
The check whether the presently available multiresonance coupled channel analyses can explain the more complex processes is made. The process chosen is a well measured proces of eta production in proton proton collisions.
Using the Morse-theoretic techniques introduced by Hitchin, we prove that the moduli space of $\Sp(2p,2q)$-Higgs bundles over a compact Riemann surface of genus $g\geq 2$ is connected. In particular, this implies that the moduli space of representations of the fundamental group of the surface in $\Sp(2p,2q)$ is connected.
The role of entanglement and quantum correlations in complex physical systems and quantum information processing devices has become a topic of intense study in the past two decades. In this work we present new tools for learning about entanglement and quantum correlations in dynamical systems where the quantum states are mixed and the eigenvalue spectrum is highly degenerate. We apply these results to the Deterministic quantum computing with one qubit (DQC1) computation model and show that the states generated in a DQC1 circuit have an eigenvalue structure that makes them difficult to entangle, even when they are relatively far from the completely mixed state. Our results strengthen the conjecture that it may be possible to find quantum algorithms that do not generate entanglement and yet still have an exponential advantage over their classical counterparts.
We describe the class of functions $f: R^n\to R^m$ which transform a vector Brownian Motion into a martingale and use this description to give martingale characterization of the general measurable solution of the multidimensional Cauchy functional equation.
We study the spectrum of the isoscalar pentaquark $udsc\overline{c}$, of either positive or negative parity, in a constituent quark model with linear confinement and a flavor-spin hyperfine interaction previously extended to SU(4) and used to describe the spectrum of the $uudc\overline{c}$ pentaquarks observed at LHCb in 2019. For positive parity we make a distinction between the case where one unit of angular momentum is located in the subsystem of four quarks and the case where the angular momentum is located in the relative motion between a ground state four-quark subsystem and the antiquark. The novelty is that we introduce the coupling between different flavor states, due to the breaking of exact SU(4)-flavor symmetry of the Hamiltonian model, both for positive and negative parity states. An important consequence is that the lowest state, located at 4404 MeV, has quantum numbers $J^P$ = $1/2^-$ while without coupling the lowest state has $J^P$ = $1/2^+$ or $3/2^+$.