ShantanuT01/DACTYL-Pretraining huggingface dataset:
We analyse the relationship between classical chaos and particle creation in Robertson-Walker cosmological models with gravity coupled to a scalar field. Within our class of models chaos and particle production are seen to arise in the same cases. Particle production is viewed as the seed of decoherence, which both enables the quantum to classical transition, and ensures that the correspondence between the quantum and classically chaotic models will be valid
Authors Hohmann and Wohlfarth have put forward a no-go theorem for bimetric gravity with positive and negative mass in arXiv:0908.3384v1 [gr-qc]. This comment shows that their no-go theorem does not apply to arXiv:0807.2838v1 [gr-qc].
We study nuclear effects of charged current deep inelastic neutrino-iron scattering in the framework of a chi^2 analysis of parton distribution functions (PDFs). We extract a set of iron PDFs which are used to compute x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure functions which are required in global analyses of free nucleon PDFs. We compare our results with nuclear correction factors from neutrino-nucleus scattering models and correction factors for charged-lepton--iron scattering. We find that, except for very high x_Bj, our correction factors differ in both shape and magnitude from the correction factors of the models and charged-lepton scattering.
We study the behavior of fermion liquid defined on hexagonal and triangular lattices with short-range repulsion at half filling. In strong coupling limit the Mott-Hubbard phase state is present, the main peculiarity of insulator state is a doubled cell of the lattices. In the insulator state at half filling fermions with momenta $k$ and $k+\pi$ are coupled via the effective $\lambda$-field, the gap in the spectrum of quasi-particle excitations opens and the Mott phase transition is occured at a critical value of the one-site Hubbard repulsion~$U_c$. $U_c=3.904$ and $U_c=5.125$ are calculated values for hexagonal and triangular lattices, respectively. Depending on the magnitude of the short-range repulsion, the gap in the spectrum and the energy of the ground state are calculated. The proposed approach is universal; it is implemented for an arbitrary dimension and symmetry of the lattice for fermions models with short-range repulsion.
We study analogues of the usual Picard group for smooth analytic or non-singular algebraic varieties but instead of line bundles we study line bundles with a connection. We choose an approach which works for both cases.
Fast radio burst (FRBs) are an exciting class of bright, extragalactic, millisecond radio transients. The recent development of large field-of-view (FOV) radio telescopes has caused a rapid rise in the number of identified single burst and repeating FRBs. This has allowed for the extensive multi-wavelength follow-up to search for the potential counterparts predicted by theoretical models. New observations of similar radio transients in Galactic magnetars like SGR 1935+2154 have continued to motivate the search for rapid optical and very-high-energy (VHE, >100 GeV) counterparts. Since 2016 VERITAS has engaged in an FRB observing campaign to search for the prompt optical, and VHE emission from multiple repeating FRBs. We present these new results from VERITAS observations of five repeating sources including data taken simultaneously with bursts observed by the CHIME radio telescope.
We explore the possibility of measuring the CKM parameter gamma using CP tagged decays at a very high luminosity e+e- B Factory. A new collider capable of integrating as much as 10 inverse attobarns per year is being discussed as a possible future for SLAC beyond the current PEP-II program, and could also be in the future of KEK. In two years of operation, it could be possible for a successor to BaBar or Belle to accumulate a sample of one million CP tagged B decays. We find that a theoretically clean extraction of gamma with uncertainty less than 5 degrees may be achievable in the analysis of such a data set.
Single crystals of a new ternary aluminide ErV$_2$Al$_{20}$ were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV$_2$Al$_{20}$ is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment $\mu_{eff}$ = 9.27(1) $\mu_B$ and Curie-Weiss temperature $\Theta_{CW}$ = -0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatures that is attributed to the presence of a low-energy Einstein mode with characteristic temperature $\Theta_E$ = 44 K, approximately twice as high as in the isostructural 'Einstein solid' VAl$_{10.1}$.
We classify orbits of stars that are bound to central black holes in galactic nuclei. The stars move under the combined gravitational influences of the black hole and the central star cluster. Within the sphere of influence of the black hole, the orbital periods of the stars are much shorter than the periods of precession. We average over the orbital motion and end up with a simpler problem and an extra integral of motion: the product of the black hole mass and the semimajor axis of the orbit. Thus the black hole enforces some degree of regularity in its neighborhood. Well within the sphere of influence, (i) planar, as well as three dimensional, axisymmetric configurations-both of which could be lopsided-are integrable, (ii) fully three dimensional clusters with no spatial symmetry whatsover must have semi-regular dynamics with two integrals of motion. Similar considerations apply to stellar orbits when the black hole grows adiabatically. We introduce a family of planar, non-axisymmetric potential perturbations, and study the orbital structure for the harmonic case in some detail. In the centered potentials there are essentially two main families of orbits: the familiar loops and lenses, which were discussed in Sridhar and Touma (1997, MNRAS, 287, L1-L4). We study the effect of lopsidedness, and identify a family of loop orbits, whose orientation reinforces the lopsidedness, an encouraging sign for the construction of self-consistent models of eccentric, discs around black holes, such as in M31 and NGC 4486B.
The brane-worlds model was inspired partly by Kaluza-Klein's theory, where the gravitation and the gauge fields are obtained of a geometry of higher dimension (bulk). Such a model has been showing positive in the sense of we find perspectives and probably deep modifications in the physics, such as: Unification in a scale TeV, quantum gravity in this scale and deviation of Newton's law for small distances. One of the principles of this model is to suppose a space-time embedded in a bulk of high dimension. In this note it is shown, basing on the theorem of Collinson-Szekeres, that the space-time of Schwarzschild cannot be embedded locally and isometrically in a bulk of five dimensions with constant curvature,(for example ADS-5). From the point of view of the semi-Riemannian geometry this last result consists constraints to the model brane-world.
A scalar theory of gravity with a preferred reference frame is presented. It is insisted on the dynamics, which involves a (non-trivial) extension of Newton's second law, and on the new version (v2) with isotropic space metric. We display the energy conservation equation obtained with v2. Then the principles of the asymptotic post-Newtonian approximation are discussed in some detail. The results of its application to the motion of a small extended body in a weakly-gravitating system are given and discussed: the weak equivalence principle was violated in v1, due to its anisotropic space metric (as the standard Schwarzschild metric), but is valid with v2.
The {\em rainbow state} denotes a set of valence bond states organized concentrically around the center of a spin 1/2 chain. It is the ground state of an inhomogeneous XX Hamiltonian and presents maximal violation of the area law of entanglement entropy. Here, we add a tunable exchange coupling constant at the center, $\gamma$, and show that it induces entanglement transitions of the ground state. At very strong inhomogeneity, the rainbow state survives for $0 \leq \gamma \leq 1$, while outside that region the ground state is a product of dimers. In the weak inhomogeneity regime the entanglement entropy satisfies a volume law, derived from CFT in curved spacetime, with an effective central charge that depends on the inhomogeneity parameter and $\gamma$. In all regimes we have found that the entanglement properties are invariant under the transformation $\gamma \longleftrightarrow 1 - \gamma$, whose fixed point $\gamma = \frac{1}{2}$ corresponds to the usual rainbow model. Finally, we study the robustness of non trivial topological phases in the presence of the defect.
In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed 2 and 3 dimensional simulations of cloud-ISM interactions. Our simulations track the hydrodynamics and time dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.
Glaucoma is a major eye disease, leading to vision loss in the absence of proper medical treatment. Current diagnosis of glaucoma is performed by ophthalmologists who are often analyzing several types of medical images generated by different types of medical equipment. Capturing and analyzing these medical images is labor-intensive and expensive. In this paper, we present a novel computational approach towards glaucoma diagnosis and localization, only making use of eye fundus images that are analyzed by state-of-the-art deep learning techniques. Specifically, our approach leverages Convolutional Neural Networks (CNNs) and Gradient-weighted Class Activation Mapping (Grad-CAM) for glaucoma diagnosis and localization, respectively. Quantitative and qualitative results, as obtained for a small-sized dataset with no segmentation ground truth, demonstrate that the proposed approach is promising, for instance achieving an accuracy of 0.91$\pm0.02$ and an ROC-AUC score of 0.94 for the diagnosis task. Furthermore, we present a publicly available prototype web application that integrates our predictive model, with the goal of making effective glaucoma diagnosis available to a wide audience.
We make the simple, and yet deep, observation that a regular conditional distribution (rcd) almost surely trivialises the conditioning $\sigma$-algebra if and only if there exists a "measurable selection" of regular conditional distributions for almost all the measures arising out of the original rcd.
The radiative recombination, Shokley-Read recombination, frontal-surface and rear-surface recombination and the recombination at the heterojunction boundaries and the recombination in the space charge region are considered in the calculation of the multijunction solar cell (MSC) efficiency. The calculation is performed by a self-consistent solution of the equations for the photocurrent and photovoltage, as well as the heat balance equation. A cooling of MSC with the increase of the number of cells n and the improvement in the heat dissipation is regarded. It was found that, as the number of cells n is increased, narrowing of spectral range for each cell causes additional reduction of current. A substantial increase in the MSC efficiency can be achieved by improving the heat extraction using radiators and increasing emissivity. A comparison is made between the calculated and experimental efficiency values. A rather good agreement was found. A comparison between this calculation and other formalisms is given.
In this paper, we propose a general means of estimating the rate at which convergences in law occur. Our approach, which is an extension of the classical Stein-Tikhomirov method, rests on a new pair of linear operators acting on characteristic functions. In principle, this method is admissible for any approximating sequence and any target, although obviously the conjunction of several favorable factors is necessary in order for the resulting bounds to be of interest. As we briefly discuss, our approach is particularly promising whenever some version of Stein's method applies. We apply our approach to two examples. The first application concerns convergence in law towards targets $F_\infty$ which belong to the second Wiener chaos (i.e. $F_{\infty}$ is a linear combination of independent centered chi-squared rvs). We detail an application to $U$-statistics. The second application concerns convergence towards targets belonging to the generalized Dickman family of distributions. We detail an application to a theorem from number theory. In both cases our method produces bounds of the correct order (up to a logarithmic loss) in terms of quantities which occur naturally in Stein's method.
The superstring in $D\!=\!3,4$ and 6 is invariant under an $N\!=\!D\!-\!2$ superconformal algebra based on $\widehat{S^{D-3}}$. There is a direct relationship between this (world-sheet) symmetry and the super-Poincar\'e (target space) symmetry. We establish this relationship using the light-cone gauge, show how the statement generalizes to $D\!=\!10$ and examine the properties of the $N\!=\!8$ superconformal algebra and the possible implications of its existence.
Astrophysical fluids are generically turbulent, which means that frozen-in magnetic fields are, at least, weakly stochastic. Therefore realistic studies of astrophysical magnetic reconnection should include the effects of stochastic magnetic field. In the paper we discuss and test numerically the Lazarian & Vishniac (1999) model of magnetic field reconnection of weakly stochastic fields. The turbulence in the model is assumed to be subAlfvenic, with the magnetic field only slightly perturbed. The model predicts that the degree of magnetic field stochasticity controls the reconnection rate and that the reconnection can be fast independently on the presence or absence of anomalous plasma effects. For testing of the model we use 3D MHD simulations. To measure the reconnection rate we employ both the inflow of magnetic flux and a more sophisticated measure that we introduce in the paper. Both measures of reconnection provide consistent results. Our testing successfully reproduces the dependences predicted by the model, including the variations of the reconnection speed with the variations of the injection scale of turbulence driving as well as the intensity of driving. We conclude that, while anomalous and Hall-MHD effects in particular circumstances may be important for the initiation of reconnection, the generic astrophysical reconnection is fast due to turbulence, irrespectively of the microphysical plasma effects involved. This conclusion justifies numerical modeling of many astrophysical environments, e.g. interstellar medium, for which plasma-effect-based collisionless reconnection is not applicable.
The dynamics of sandpile models are mapped to discrete interface equations. We study in detail the Bak-Tang-Wiesenfeld model, a stochastic model with random thresholds, and the Manna model. These are, respectively, discretizations of the quenched Edwards-Wilkinson equation with columnar, point-like and correlated noise, with the constraint that the interface velocity is either zero or exactly one. The constraint, embedded in the sandpile rules, gives rise to another noise component. This term has for the Bak-Tang-Wiesenfeld model long-range on-site correlations and reveals that with open boundary conditions there is no spatial translational invariance.
We argue that the spiral can, in presence of a maximum principle, be of maximal rank at a boundary, but does not preserve hypoellipticity.
By using an ancilla qubit as a mediator, two distant qubits can undergo a non-local entangling unitary operation. This is desirable for when attempting to scale up or distribute quantum computation by combining fixed static local sets of qubits with ballistic mediators. Using a model driven by measurements on the ancilla, it is possible to generate a maximally entangling CZ gate while only having access to a less entangling gate between the pair qubits and the ancilla. However this results in a stochastic process of generating control phase rotation gates where the expected time for success does not correlate with the entangling power of the connection gate. We explore how one can use feedback into the preparation and measurement parameters of the ancilla to speed up the expected time to generate a CZ gate between a pair of separated qubits and to leverage stronger coupling strengths for faster times. Surprisingly, by choosing an appropriate strategy, control of a binary discrete parameter achieves comparable speed up to full continuous control of all degrees of freedom of the ancilla.
We establish a novel procedure to analyze the entanglement properties of extremal density matrices depending on the parameters of a finite dimensional Hamiltonian. It was applied to a general 2-qubit Hamiltonian which could exhibit Kramers degeneracy. This is done through the extremal density matrix formalism, which allows to extend the conventional variational principle to mixed states. By applying the positive partial transpose criterion in terms of the Correlation and Schlienz-Mahler matrices on the extremal density matrices, we demonstrate that it is possible to reach both pure and mixed entangled states, changing properly the parameters of the Hamiltonian. For time-reversal invariant Hamiltonians, the extremal pure states can be entangled or not and we prove that they are not time-reversal invariants. For extremal mixed states we have in general 5 possible cases: three of them are entangled and the other two separable.
Eighth-BPS local operators in N=4 SYM are dual to quantum states arising from the quantization of a moduli space of giant gravitons in AdS5xS5. Earlier results on the quantization of this moduli space give a Hilbert space of multiple harmonic oscillators in 3 dimensions. We use these results, along with techniques from fuzzy geometry, to develop a map between quantum states and brane geometries. In particular there is a map between the oscillator states and points in a discretization of the base space in the toric fibration of the moduli space. We obtain a geometrical decomposition of the space of BPS states with labels consisting of U(3) representations along with U(N) Young diagrams and associated group theoretic multiplicities. Factorization properties in the counting of BPS states lead to predictions for BPS world-volume excitations of specific brane geometries. Some of our results suggest an intriguing complementarity between localisation in the moduli space of branes and localisation in space-time.
Fermi coordinates are constructed as exact functions of the Schwar\-zschild coordinates around the world line of a static observer in the equatorial plane of the Schwarzschild spacetime modulo a single impact parameter determined implicitly as a function of the latter coordinates. This illustrates the difficulty of constructing explicit exact Fermi coordinates even along simple world lines in highly symmetric spacetimes.
Multiple object tracking faces several challenges that may be alleviated with trajectory information. Knowing the posterior locations of an object helps disambiguating and solving situations such as occlusions, re-identification, and identity switching. In this work, we show that trajectory estimation can become a key factor for tracking, and present TrajE, a trajectory estimator based on recurrent mixture density networks, as a generic module that can be added to existing object trackers. To provide several trajectory hypotheses, our method uses beam search. Also, relying on the same estimated trajectory, we propose to reconstruct a track after an occlusion occurs. We integrate TrajE into two state of the art tracking algorithms, CenterTrack [63] and Tracktor [3]. Their respective performances in the MOTChallenge 2017 test set are boosted 6.3 and 0.3 points in MOTA score, and 1.8 and 3.1 in IDF1, setting a new state of the art for the CenterTrack+TrajE configuration
In this paper we construct distance-regular graphs admitting a transitive action of the five sporadic simple groups discovered by E. Mathieu, the Mathieu groups $M_{11}$, $M_{12}$, $M_{22}$, $M_{23}$ and $M_{24}$. From the code spanned by the adjacency matrix of the strongly regular graph with parameters (176,70,18,34) we obtain block designs having the full automorphism groups isomorphic to the Higman-Sims finite simple group. Further, we discuss a possibility of permutation decoding of the codes spanned by the adjacency matrices of the graphs constructed and find small PD-sets for some of the codes.
Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet we remain blind to its main driver, the magnetic field. Here we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg II $h$ & $k$ and Mn I) and visible (Fe I) lines. We infer the longitudinal magnetic field from the photosphere to the very upper chromosphere. At the top of the plage chromosphere the field strengths reach more than 300 gauss, strongly correlated with the Mg II $k$ line core intensity and the electron pressure. This unique mapping shows how the magnetic field couples the different atmospheric layers and reveals the magnetic origin of the heating in the plage chromosphere.
Generative adversarial networks (GANs) are one of the most widely adopted semisupervised and unsupervised machine learning methods for high-definition image, video, and audio generation. In this work, we propose a new type of architecture for quantum generative adversarial networks (entangling quantum GAN, EQ-GAN) that overcomes some limitations of previously proposed quantum GANs. Leveraging the entangling power of quantum circuits, EQ-GAN guarantees the convergence to a Nash equilibrium under minimax optimization of the discriminator and generator circuits by performing entangling operations between both the generator output and true quantum data. We show that EQ-GAN has additional robustness against coherent errors and demonstrate the effectiveness of EQ-GAN experimentally in a Google Sycamore superconducting quantum processor. By adversarially learning efficient representations of quantum states, we prepare an approximate quantum random access memory (QRAM) and demonstrate its use in applications including the training of quantum neural networks.