ShantanuT01/DACTYL-Pretraining huggingface dataset:
We use the Keck Deep Fields UGRI catalog of z~4, 3, and 2 UV-selected galaxies to study the evolution of the rest-frame 1700A luminosity density at high redshift. The ability to reliably constrain the contribution of faint galaxies is critical and our data do so as they reach to M*+2 even at z~4 and deeper still at lower redshifts. We find that the luminosity density at high redshift is dominated by the hitherto poorly studied galaxies fainter than L*, and, indeed, the the bulk of the UV light in the high-z Universe comes from galaxies in the luminosity range L=0.1-1L*. It is these faint galaxies that govern the behavior of the total UV luminosity density. Overall, there is a gradual rise in luminosity density starting at z~4 or earlier, followed by a shallow peak or a plateau within z~3--1, and then followed by the well-know plunge at lower redshifts. Within this total picture, luminosity density in sub-L* galaxies evolves more rapidly at high redshift, z>~2, than that in more luminous objects. However, this is reversed at lower redshifts, z<~1, a reversal that is reminiscent of galaxy downsizing. Within the context of the models commonly used in the observational literature, there seemingly aren't enough faint or bright LBGs to maintain ionization of intergalactic gas even as late as z~4. This is particularly true at earlier epochs and even more so if the faint-end evolutionary trends we observe at z~3 and 4 continue to higher redshifts. Apparently the Universe must be easier to reionize than some recent studies have assumed. Nevertheless, sub-L* galaxies do dominate the total UV luminosity density at z>~2 and this dominance further highlights the need for follow-up studies that will teach us more about these very numerous but thus far largely unexplored systems.
We study for the first time the low-frequency ($\sim$150 MHz) radio brightness distribution of Arp~299 at subarcsecond resolution, tracing in both compact and extended emission regions the local spectral energy distribution (SED) in order to characterize the dominant emission and absorption processes. We analysed the spatially resolved emission of Arp 299 revealed by 150 MHz international baseline Low-Frequency Array (LOFAR) and 1.4, 5.0, and 8.4 GHz Very Large Array (VLA) observations. We present the first subarcsecond (0.4"$\sim$100~pc) image of the whole Arp~299 system at 150~MHz. The high surface brightness sensitivity of our LOFAR observations ($\sim$100 $\mu$Jy/beam) allowed us to detect all of the nuclear components detected at higher frequencies, as well as the extended steep-spectrum emission surrounding the nuclei. We obtained spatially resolved, two-point spectral index maps for the whole galaxy: the compact nuclei show relatively flat spectra, while the extended, diffuse component shows a steep spectrum. We fitted the radio SED of the nuclear regions using two different models: a continuous free-free medium model and a clumpy model. The continuous model can explain the SED of the nuclei assuming a population of relativistic electrons subjected to synchrotron, bremsstrahlung, and ionization losses. The clumpy model fits assuming relativistic electrons with negligible energy losses, and thermal fractions that are more typical of star-forming galaxies than those required for the continuous model. Our results confirm the usefulness of combining spatially resolved radio imaging at both MHz and GHz frequencies to characterize in detail the radio emission properties of LIRGs from the central 100 pc out to the kiloparsec galaxy-wide scales.
Let $\varphi_1,\ldots ,\varphi_r\in \mathbb Z[z_1,\ldots z_k]$ be integral linear combinations of elementary symmetric polynomials with $\text{deg}(\varphi_j)=k_j$ $(1\le j\le r)$, where $1\le k_1<k_2<\ldots <k_r=k$. Subject to the condition $k_1+\ldots +k_r\ge \tfrac{1}{2}k(k-1)+2$, we show that there is a paucity of non-diagonal solutions to the Diophantine system $\varphi_j(\mathbf x)=\varphi_j(\mathbf y)$ $(1\le j\le r)$.
A complete analysis of the electroweak precision observables is performed within a recently proposed minimal composite Higgs model, realized as a 5-dimensional warped compactification. In particular, we compute Z->bb and the one-loop correction to the rho parameter. We find that oblique data can be easily reproduced without a significant amount of tuning in the parameters of the model, while Z->bb imposes a stronger constraint. As a consequence of the latter, some of the new fermionic resonances must have mass around 4 TeV, which corresponds to an electroweak fine tuning of a few percent. Other resonances, such as Z', can be lighter in sizeable portions of the parameter space. We discuss in detail the origin of the Z->bb constraint and we suggest several possible avenues beyond the minimal model for weakening it.
The quarks of quark models cannot be identified with the quarks of the QCD Lagrangian. We review the restrictions that gauge field theories place on any description of physical (colour) charges. A method to construct charged particles is presented. The solutions are applied to a variety of applications. Their Green's functions are shown to be free of infra-red divergences to all orders in perturbation theory. The interquark potential is analysed and it is shown that the interaction responsible for anti-screening results from the force between two separately gauge invariant constituent quarks. A fundamental limit on the applicability of quark models is identified.
The exact ground-state exchange-correlation functional of Kohn-Sham density functional theory yields the exact transmission through an Anderson junction at zero bias and temperature. The exact impurity charge susceptibility is used to construct the exact exchange-correlation potential. We analyze the successes and limitations of various types of approximations, including smooth and discontinuous functionals of the occupation, as well as symmetry-broken approaches.
In the present work we study the consequences of considering a new family of single-field inflation models, called power-law plateau inflation, in the warm inflation framework. We consider the inflationary expansion is driven by a standard scalar field with a decay ratio $\Gamma$ having a generic power-law dependence with the scalar field $\phi$ and the temperature of the thermal bath $T$ given by $\Gamma(\phi,T)=C_{\phi}\,\frac{T^m}{\phi^{m-1}}$. Assuming that our model evolves according to the strong dissipative regime, we study the background and perturbative dynamics, obtaining the most relevant inflationary observables as the scalar power spectrum, the scalar spectral index and its running, and the tensor-to-scalar ratio. The free parameters characterizing our model are constrained by considering the essential condition for warm inflation, the conditions for the model evolves according to the strong dissipative regime, and the 2015 Planck results through the $n_s-r$ plane. For completeness, we study the predictions in the $n_s-dn_s/d\ln k$ plane. The model is consistent with a strong dissipative dynamics and predicts values for the tensor-to-scalar ratio and for the running of the scalar spectral index consistent with current bounds imposed by Planck, and we conclude that the model is viable.
Symmetric hyperbolic systems of equations are explicitly constructed for a general class of tensor fields by considering their structure as r-fold forms. The hyperbolizations depend on 2r-1 arbitrary timelike vectors. The importance of the so-called "superenergy" tensors, which provide the necessary symmetric positive matrices, is emphasized and made explicit. Thereby, a unified treatment of many physical systems is achieved, as well as of the sometimes called "higher order" systems. The characteristics of these symmetric hyperbolic systems are always physical, and directly related to the null directions of the superenergy tensor, which are in particular principal null directions of the tensor field solutions. Generic energy estimates and inequalities are presented too.
Electron transport is theoretically investigated in a molecular device made of anthracene molecule attached to the electrodes by thiol end groups in two different configurations (para and meta, respectively). Molecular system is described by a simple Huckel-like model (with non-orthogonal basis set of atomic orbitals), while the coupling to the electrodes is treated through the use of Newns-Anderson chemisorption theory (constant density of states within energy bandwidth). Transport characteristics (current-voltage and conductance-voltage) are calculated from the transmission function in the standard Landauer formulation. The essential question of quantum interference is discussed in detail. The results have shown a striking variation of transport properties of the device depending on the character of molecular binding to the electrodes.
The knowledge of electron and hole g-factors, their control and engineering are key for the usage of the spin degree of freedom for information processing in solid state systems. The electronic g-factor will be materials dependent, the effect being larger for materials with large spin-orbit coupling. Since electrons can be individually trapped into quantum dots in a controllable manner, they may represent a good platform for the implementation of quantum information processing devices. Here we use self-assembled quantum dots of InAs embedded in GaAs for the g-factor control and engineering.
Semimetallic tungsten ditelluride (WTe2) displays an extremely large non-saturating magnetoresistance (XMR), which is the subject of intense interest. This phenomenon is thought to arise from the combination of perfect n-p charge compensation with low carrier densities in WTe2 and presumably details of its band structure. Recently, "spin texture" induced by strong spin-orbital coupling (SOC) has been observed in WTe2 by angle-resolved photoemission spectroscopy (ARPES). This provides a mechanism for protecting backscattering for the states involved and thus was proposed to play an important role in the XMR of WTe2. Here, based on our density functional calculations for bulk WTe2, we found a strong Rashba spin-orbit effect in the calculated band structure due to its non-centrosymmetric structure. This splits bands and two-fold spin degeneracy of bands is lifted. A prominent Umklapp interference pattern (a spectroscopic feature with involving reciprocal lattice vectors) can be observed by scanning tunneling microscopic (STM) measurements on WTe2 surface at 4.2 K. This differs distinctly from the surface atomic structure demonstrated at 77 K. The energy dependence of Umklapp interference shows a strong correspondence with densities of states integrated from ARPES measurement, manifesting a fact that the bands are spin-split on the opposites side of Gamma point. Spectroscopic survey reveals the ratio of electron/hole asymmetry changes alternately with lateral locations along b axis, providing a microscopic picture for double-carrier transport of semimetallic WTe2. The calculated band structure and Fermi surface is further supported by our ARPES results and Shubnikov-de Haas (SdH) oscillations measurements.
A sketch of the proof of strong cosmic censorship is presented for a class of solutions of the Einstein-Maxwell equations, those with polarized Gowdy symmetry. A key element of the argument is the observation that by means of a suitable choice of variables the central equations in this problem can be written in a form where they are identical to the central equations for general (i.e. non-polarized) vacuum Gowdy spacetimes. Using this it is seen that the results of Ringstr\"{o}m on strong cosmic censorship in the vacuum case have implications for the Einstein-Maxwell case. Working out the geometrical meaning of these analytical results leads to the main conclusion.
We describe the transition from a ferromagnetic phase, to a disordered para- magnetic phase, which occurs in one-dimensional Kondo lattice models with partial conduction band filling. The transition is the quantum order-disorder transition of the transverse-field Ising chain, and reflects double-exchange ordered regions of localized spins being gradually destroyed as the coupling to the conduction electrons is reduced. For incommensurate conduction band filling, the low-energy properties of the localized spins near the transition are dominated by anomalous ordered (disordered) regions of localized spins which survive into the paramagnetic (ferromagnetic) phase. Many interesting properties follow, including a diverging susceptibility for a finite range of couplings into the paramagnetic phase. Our critical line equation, together with numerically determined transition points, are used to determine the range of the double-exchange interaction. Models we consider are the spin 1/2 Kondo lattices with antiferromagnetic (Kondo) coupling, with ferromagnetic (Hund's rule) coupling, and the Kondo lattice with repulsive interactions between the conduction electrons.
In this article, we investigate the quantitative unique continuation properties of real-valued solutions to elliptic equations in the plane. Under a general set of assumptions on the operator, we establish quantitative forms of Landis' conjecture. Of note, we prove a version of Landis' conjecture for solutions to $-\Delta u + V u = 0$, where $V$ is a bounded function whose negative part exhibits polynomial decay at infinity. The main mechanism behind the proofs is an order of vanishing estimate in combination with an iteration scheme. To prove the order of vanishing result, we present a new idea for constructing positive multipliers and use it reduce the equation to a Beltrami system. The resulting first-order equation is analyzed using the similarity principle and the Hadamard three-quasi-circle theorem.
We present a discussion of the admittance (ac-conductance) and nonlinear I-V-characteristic for a number of mesoscopic conductors. Our approach is based on a generalization of the scattering approach which now includes the effects of the (long-range) Coulomb interaction. We discuss the admittance of a wire with an impurity and with a nearby gate. We extend a discussion of the low-frequency admittance of a quantum point contact to investigate the effects of the gates used to form the contact. We discuss the nonlinear I-V characteristic of a resonant double barrier structure and discuss the admittance for the double barrier for a large range of frequencies. Our approach emphasizes the overall conservation of charge (gauge invariance) and current conservation and the resulting sum rules for the admittance matrix and nonlinear transport coefficients.
The spin one-half Heisenberg chain with $U_q[SU(2)]$ symmetry is studied via density-matrix renormalization. Ground-state energy and $q$-symmetric correlation functions are calculated for the non-hermitian case $q=\exp(i\pi/(r+1))$ with integer $r$. This gives bulk and surface exponents for (para)fermionic correlations in the related Ising and Potts models. The case of real $q$ corresponding to a diffusion problem is treated analytically.
It is shown how to construct Keldysh diagram technique for pseudo - particle approach to the Hubbard model. We propose self consistent equations for pseudo particle and electron Green functions in Keldysh diagram technique. Nonlocal effects (spatial dispersion) are included in single impurity problem in this method. Thus we can get rid of the artificial central peak (of Kondo type) in the density of states which is inevitable in Dynamical Mean Field Theory (DMFT). The changes in the density of states for 2D Hubbard model due to variation of Coulomb repulsion U and electron concentration are analyzed.
We present the first results on galaxy metallicity evolution at z>3 from two projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE (Assessing the Mass Abundance redshift Evolution). These projects use deep near-infrared spectroscopic observations of a sample of ~40 LBGs to estimate the gas-phase metallicity from the emission lines. We derive the mass-metallicity relation at z$>$3 and compare it with the same relation at lower redshift. Strong evolution from z=0 and z=2 to z=3 is observed, and this finding puts strong constrains on the models of galaxy evolution. These preliminary results show that the effective oxygen yields does not increase with stellar mass, implying that the simple outflow model does not apply at z>3.
The long-term variability of the multiwavelength blazar emission can be interpreted in terms of orientation variations of a helical, inhomogeneous, non-thermally emitting jet, possibly caused by the orbital motion of the parent black hole in a binary system (Villata & Raiteri 1999). The helical-jet model is here applied to explain the quasi-periodic radio-optical light curves and the broad-band spectral energy distributions (SEDs) of the BL Lac object AO 0235+16. Through a suitable choice of the model parameters, the helix rotation can well account for the periodicity of the main radio and optical outbursts and for the corresponding SED variability, while the interspersed minor radio events could be interpreted as due either to some local distortions of the helical structure or to other phenomena contributing to the source emission. In particular, the probable existence of flow instabilities provides a viable interpretation for the non-periodic features.
We revisit the problem of radial pulsations of neutron stars by computing four general-relativistic polytropic models, in which "density" and "adiabatic index" are involved with their discrete meanings: (i) "rest-mass density" or (ii) "mass-energy density" regarding the density, and (i) "constant" or (ii) "variable" regarding the adiabatic index. Considering the resulting four discrete combinations, we construct corresponding models and compute for each model the frequencies of the lowest three radial modes. Comparisons with previous results are made. The deviations of respective frequencies of the resolved models seem to exhibit a systematic behavior, an issue discussed here in detail.
We present the first long-term optical and infrared study of the optical counterpart to the source RX J0812.4-3114, an X-ray pulsar with a Be type companion. During the period covered by the observations the profile of some Balmer lines changed from absorption to emission and back again to absorption. Contemporaneously, the infrared magnitudes varied by more than 0.8 mag. This long-term variability is interpreted as the formation and subsequent dissipation of the Be star's disc. The building up of the disc ended up in an active X-ray state characterised by regular outbursts occurring at 80 day intervals. The overall duration of the formation/dissipation of the disc is found to be < 4.3 years. Optical spectroscopic and infrared photometric observations were used to refine the spectral type of the primary (B0.2IV) and to monitor the circumstellar envelope around the Be star. UBVRI and uvby\beta photometric observations allowed the determination of the astrophysical parameters of the optical companion.
Spin-orbital liquids are quantum disordered states in systems with entangled spin and orbital degrees of freedom. We study exactly solvable spin-orbital models in two dimensions with selected Heisenberg-, Kitaev-, and $\Gamma$-type interactions, as well as external magnetic fields. These models realize a variety of spin-orbital-liquid phases featuring dispersing Majorana fermions with Fermi surfaces, nodal Dirac or quadratic band touching points, or full gaps. In particular, we show that Zeeman magnetic fields can stabilize nontrivial flux patterns and induce metamagnetic transitions between states with different topological character. Solvable nearest-neighbor biquadratic spin-orbital perturbations can be tuned to stabilize zero-energy flat bands. We discuss in detail the examples of $\mathrm{SO}(2)$- and $\mathrm{SO}(3)$-symmetric spin-orbital models on the square and honeycomb lattices, and use group-theoretical arguments to generalize to $\mathrm{SO}(\nu)$-symmetric models with arbitrary integer $\nu > 1$. These results extend the list of exactly solvable models with spin-orbital-liquid ground states and highlight the intriguing general features of such exotic phases. Our models are thus excellent starting points for more realistic modellings of candidate materials.
We study the all-optical time-control of the strong coupling between a single cascade three-level quantum emitter and a microcavity. We find that only specific arrival-times of the control pulses succeed in switching-off the Rabi oscillations. Depending on the arrival times of control pulses, a variety of exotic non-adiabatic cavity quantum electrodynamics effects can be observed. We show that only control pulses with specific arrival times are able to suddenly switch-off and -on first-order coherence of cavity photons, without affecting their strong coupling population dynamics. Such behavior may be understood as a manifestation of quantum complementarity.
We report the discovery of a new spin glass ground state in the transition metal monosilicides with the B20 crystallographic structure. Magnetic, transport, neutron and muon investigation of the solid solution Mn$_{1-x}$Co$_{x}$Si have revealed a new dome in the phase diagram with evidence of antiferromagnetic interactions. For Mn rich compounds, a sharp decrease of the Curie temperature is observed upon Co doping and neutron elastic scattering shows that helimagnetic order of MnSi persists up to $x=0.05$ with a shortening of the helix period. For higher Co ($0.05<x<0.90$) concentrations, the Curie-Weiss temperature changes sign and the system enters a spin glass state upon cooling ($T_g=9$ K for $x_{Co}=0.50$), due to chemical disorder. In this doping range, a minimum appears in the resistivity, attributed to scattering of conduction electron by localized magnetic moments.
We present a method for handling view-dependent information in radiance fields to help with convergence and quality of 3D reconstruction. Radiance fields with view-dependence suffers from the so called shape-radiance ambiguity, which can lead to incorrect geometry given a high angular resolution of view-dependent colors. We propose the addition of a difference plane in front of each camera, with the purpose of separating view-dependent and Lambertian components during training. We also propose an additional step where we train, but do not store, a low-resolution view-dependent function that helps to isolate the surface if such a separation is proven difficult. These additions have a small impact on performance and memory usage but enables reconstruction of scenes with highly specular components without any other explicit handling of view-dependence such as Spherical Harmonics.
In this paper we study Tur\'an and Ramsey numbers in linear triple systems, defined as $3$-uniform hypergraphs in which any two triples intersect in at most one vertex.   A famous result of Ruzsa and Szemer\'edi is that for any fixed $c>0$ and large enough $n$ the following Tur\'an-type theorem holds. If a linear triple system on $n$ vertices has at least $cn^2$ edges then it contains a {\em triangle}: three pairwise intersecting triples without a common vertex. In this paper we extend this result from triangles to other triple systems, called {\em $s$-configurations}. The main tool is a generalization of the induced matching lemma from $aba$-patterns to more general ones.   We slightly generalize $s$-configurations to {\em extended $s$-configurations}. For these we cannot prove the corresponding Tur\'an-type theorem, but we prove that they have the weaker, Ramsey property: they can be found in any $t$-coloring of the blocks of any sufficiently large Steiner triple system. Using this, we show that all unavoidable configurations with at most 5 blocks, except possibly the ones containing the sail $C_{15}$ (configuration with blocks 123, 345, 561 and 147), are $t$-Ramsey for any $t\geq 1$. The most interesting one among them is the {\em wicket}, $D_4$, formed by three rows and two columns of a $3\times 3$ point matrix. In fact, the wicket is $1$-Ramsey in a very strong sense: all Steiner triple systems except the Fano plane must contain a wicket.