ShantanuT01/DACTYL-Pretraining huggingface dataset:
A star coming too close to a supermassive black hole gets disrupted by the tidal force of the compact object in a tidal disruption event, or TDE. Following this encounter, the debris evolves into an elongated stream, half of which coming back to pericenter. Relativistic apsidal precession then leads to a self-crossing shock that initiates the formation of an accretion disc. We perform the first simulation of this process considering a realistic stellar trajectory and black hole mass, which has so far eluded investigations for computational reasons. This numerical issue is alleviated by using as initial conditions the outflow launched by the self-crossing shock according the local simulation of Lu & Bonnerot (2019). We find that the gas leaving the intersection point experiences numerous secondary shocks that result in the rapid formation of a thick and marginally-bound disc. The mass distribution features two overdensities identified as spiral shocks that drive slow gas inflow along the mid-plane. Inward motion primarily takes place along the funnels of the newly-formed torus, from which a fraction of the matter can get accreted. Further out, the gas moves outward forming an extended envelope completely surrounding the accretion flow. Secondary shocks heat the debris at a rate of a few times $10^{44} \, \rm erg \, s^{-1}$ with a large fraction likely participating to the bolometric luminosity. These results pave the way towards a complete understanding of the early radiation from TDEs that progressively becomes accessible from observations.
We present the first dynamical study of the globular cluster system of NGC 4636. This giant elliptical galaxy is claimed to be extremely dark matter dominated, according to X-ray observations. Using the VLT with FORS2/MXU, we obtained velocities for 174 globular clusters. The clusters have projected galactocentric distances in the range 4 to 70 kpc, the overwhelming majority lie within 30 kpc. We find some indication for a rotation of the red (metal-rich) clusters about the minor axis. Out to a radius of 30 kpc, we find a roughly constant projected velocity dispersion for the blue clusters of ~200 km/s. The red clusters exhibit a distinctly different behavior: at a radius of about 13 kpc, the velocity dispersion drops by ~50 km/s to about 170 km/s which then remains constant out to a radius of 30 kpc.   Using only the blue clusters as dynamical tracers, we perform Jeans-analyses for different assumptions of the orbital anisotropy. Depending on the anisotropy and the adopted M/L-values, we find that the dark matter fraction within one effective radius can vary between 20% and 50% with most a probable range between 20% and 30%. A main source of uncertainty is the ambiguity of the velocity dispersion in the outermost bin.   Although the dark halo mass still cannot be strongly constrained, NGC 4636 does not seem to be extremely dark matter dominated. The derived circular velocities are also consistent with Modified Newtonian Dynamics.
A recent paper (Phys. Rev. A 86, 034305 (2012)) proposed an entanglement concentration protocol (ECP) for less-entangled $N$-atom GHZ state with the help of the photonic Faraday rotation. It is shown that the maximally entangled atom state can be distilled from two pairs of less-entangled atom states. In this paper, we put forward an improved ECP for arbitrary less-entangled N-atom GHZ state with only one pair of less-entangled atom state, one auxiliary atom and one auxiliary photon. Moreover, our ECP can be used repeatedly to obtain a higher success probability. If consider the practical operation and imperfect detection, our protocol is more efficient. This ECP may be useful in current quantum information processing.
We determine all genus 2 curves, defined over $\mathbb C$, which have simultaneously degree 2 and 3 elliptic subcovers. The locus of such curves has three irreducible 1-dimensional genus zero components in $\mathcal M_2$. For each component we find a rational parametrization and construct the equation of the corresponding genus 2 curve and its elliptic subcovers in terms of the parameterization. Such families of genus 2 curves are determined for the first time. Furthermore, we prove that there are only finitely many genus 2 curves (up to $\mathbb C$-isomorphism) defined over $\mathbb Q$, which have degree 2 and 3 elliptic subcovers also defined over $\mathbb Q$.
In these two lectures I will discuss some outstanding problems in the standard model of cosmology, concentrating on the physics that might be related to the title of this school, ``Searching for the totally unexpected in the LHC era.'' In particular, I will concentrate on dark energy, dark matter, and inflation.
The accumulation of non-trivial geometric phases in a material's response is often a tell-tale sign of a rich underlying internal structure. Studying quantum oscillations provides one of the ways to determine these geometrical phases, such as Berry's phase, that play a central role in topological quantum materials. We report on magneto-transport measurements in ABA-trilayer graphene, the band structure of which is comprised of a weakly gapped linear Dirac band, nested within a trivial quadratic band. Here we show Shubnikov-de Haas (SdH) oscillations of the quadratic band shifted by a phase that sharply departs from the expected 2$\pi$ Berry's phase. Our analysis reveals that, surprisingly, the anomalous phase shift is non-trivial and is inherited from the non-trivial Berry's phase of the linear Dirac band due to strong filling-enforced constraints between the linear and quadratic band Fermi surfaces. Given that many topological materials contain multiple bands, our work indicates how additional bands, which are thought to obscure the analysis, can actually be exploited to tease out the subtle effects of Berry's phase.
The paper addresses inelastic spin-flip tunneling accompanied by surface spin excitations (magnons) in ferromagnetic junctions. The inelastic tunneling current is proportional to the magnon density of states which is energy-independent for the surface waves and, for this reason, cannot account for the bias-voltage dependence of the observed inelastic tunneling spectra. This paper shows that the bias-voltage dependence of the tunneling spectra can arise from the tunneling matrix elements of the electron-magnon interaction. These matrix elements are derived from the Coulomb exchange interaction using the itinerant-electron model of magnon-assisted tunneling. The results for the inelastic tunneling spectra, based on the nonequilibrium Green's function calculations, are presented for both parallel and antiparallel magnetizations in the ferromagnetic leads.
A method is presented for the analysis of the scalar potential in the general Two-Higgs-Doublet Model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the Two-Higgs-Doublet potential proposed by Gunion at al. All known results for these models follow easily as special cases from the general results. In particular, in the potential of Gunion et al. we can clarify some interesting aspects of the model with the help of the proposed method.
We present an investigation of three chemically peculiar (CP) stars and one CP star candidate which exhibit photometric periods below 12 hours. New spectroscopic observations have been acquired which confirm the peculiar nature of all objects. HD 77013 and HD 81076 are classical CP1 (Am) stars; HD 67983 is a marginal CP1 (Am: ) star, and HD 98000 is a CP2 (Ap) star. We have procured observations from the ASAS-3 and SuperWASP archives and obtained additional photometry in order to verify the results from the sky survey data. We have derived astrophysical parameters and investigated the positions of our target stars in the MBol versus log Teff diagram, from which information on evolutionary status has been derived. We present period analyses and discuss each object in detail. From the available data, we propose pulsational variability as the underlying mechanism for the variability in HD 67983, HD 77013 and HD 81076, which offer the opportunity to study the interaction of atomic diffusion and pulsation. HD 67983 and HD 77013 exhibit multiperiodic variability in the gamma Doradus frequency realm; HD 81076 is a delta Scuti star. The CP2 star HD 98000 exhibits monoperiodic variability with a frequency of f~2.148 c/d (P~0.466 d), which we interpret as the rotational period. If this assumption is correct, HD 98000 is the alpha2 Canum Venaticorum (ACV) variable with the shortest period hitherto observed and thus a very interesting object that might help to investigate the influence of rotational mixing on chemical peculiarities.
We study the binding of a holon to a doublon in a half-filled Hubbard model as the mechanism of the zero-temperature metal-insulator transition. In a spin polarized system and a non-bipartite lattice a single holon-doublon (HD) pair exhibits a binding transition (e.g., on a face-centred cubic lattice), or a sharp crossover (e.g., on a triangular lattice) corresponding well to the standard Mott transition in unpolarized systems. We extend the HD-pair study towards non-polarized systems by considering more general spin background and by treating the finite HD density within a BCS-type approximation. Both approaches lead to a discontinuous transition away from the fully polarized system and give density correlations consistent with numerical results on a triangular lattice.
With the goal of using chiral interactions at various orders to explore properties of the few-body nuclear systems, we write the recently developed local chiral interactions as spherical irreducible tensors and implement them in the hyperspherical harmonics expansion method. We devote particular attention to three-body forces at next-to-next-to leading order, which play an important role in reproducing experimental data. We check our implementation by benchmarking the ground-state properties of $^3$H, $^3$He and $^4$He against the available Monte Carlo calculations. We then confirm their order-by-order truncation error estimates and further investigate uncertainties in the charge radii obtained by using the precise muonic atom data for single-nucleon radii. Having local chiral Hamiltonians at various orders implemented in our hyperspherical harmonics suites of codes opens up the possibility to test such interactions on other light-nuclei properties, such as electromagnetic reactions.
We report on room temperature magnetoresistance and low frequency noise in sub-100nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin (0.9nm) barriers. For magnetic fields applied along the hard axis, we observe current induced magnetization switching between the antiparallel and parallel alignments at DC current densities as low as 4*106A/cm2. We attribute the low value of the critical current to the influence of localized reductions in the tunnel barrier, which affects the current distribution. The analysis of random telegraph noise, which appears in the field interval near a magnetization switch, provides an estimate to the dimension of the pseudo pinholes that trigger the magnetization switching via local spin torque. Micromagnetic simulations qualitatively and quantitatively reproduce the main experimental observations.
We study an integrable spin chain with three spin interactions and the staggered field ($\lambda$) while the latter is quenched either slowly (in a linear fashion in time ($t$) as $t/\tau$ where $t$ goes from a large negative value to a large positive value and $\tau$ is the inverse rate of quenching) or suddenly. In the process, the system crosses quantum critical points and gapless phases. We address the question whether there exist non-analyticities (known as dynamical phase transitions (DPTs)) in the subsequent real time evolution of the state (reached following the quench) governed by the final time-independent Hamiltonian. In the case of sufficiently slow quenching (when $\tau$ exceeds a critical value $\tau_1$), we show that DPTs, of the form similar to those occurring for quenching across an isolated critical point, can occur even when the system is slowly driven across more than one critical point and gapless phases. More interestingly, in the anisotropic situation we show that DPTs can completely disappear for some values of the anisotropy term ($\gamma$) and $\tau$, thereby establishing the existence of boundaries in the $(\gamma-\tau)$ plane between the DPT and no-DPT regions in both isotropic and anisotropic cases. Our study therefore leads to a unique situation when DPTs may not occur even when an integrable model is slowly ramped across a QCP. On the other hand, considering sudden quenches from an initial value $\lambda_i$ to a final value $\lambda_f$, we show that the condition for the presence of DPTs is governed by relations involving $\lambda_i$, $\lambda_f$ and $\gamma$ and the spin chain must be swept across $\lambda=0$ for DPTs to occur.
The XMM-Newton survey of the Coma cluster of galaxies covers an area of 1.86 square degrees with a mosaic of 16 pointings and has a total useful integration time of 400 ksec. Detected X-ray sources with extent less than 10" were correlated with cataloged galaxies in the Coma cluster region. The redshift information, which is abundant in this region of the sky, allowed us to separate cluster members from background and foreground galaxies. For the background sources, we recover a typical LogN-LogS in the flux range 1.e-15 - 1.e-13 ergs/s/cm^2 in the 0.5-2.0 keV band. The X-ray emission from the cluster galaxies exhibits X-ray colors typical of thermal emission. The luminosities of Coma galaxies lie in the 1.e39-1.e41 ergs/s interval in the 0.5-2.0 keV band. The luminosity function of Coma galaxies reveals that their X-ray activity is suppressed with respect to the field by a factor of 5.6, indicating a lower level of X-ray emission for a given stellar mass.
Consider a stochastic search model with resetting for an unknown stationary target $a\in\mathbb{R}$ with known distribution $\mu$. The searcher begins at the origin and performs Brownian motion with diffusion constant $D$. The searcher is also armed with an exponential clock with spatially dependent rate $r$, so that if it has failed to locate the target by the time the clock rings, then its position is reset to the origin and it continues its search anew from there. Denote the position of the searcher at time $t$ by $X(t)$. Let $E_0^{(r)}$ denote expectations for the process $X(\cdot)$.   The search ends at time $T_a=\inf\{t\ge0:X(t)=a\}$. The expected time of the search is then $\int_{\mathbb{R}}(E_0^{(r)}T_a)\thinspace\mu(da)$. Ideally, one would like to minimize this over all resetting rates $r$. We obtain quantitative growth rates for $E_0^{(r)}T_a$ as a function of $a$ in terms of the asymptotic behavior of the rate function $r$, and also a rather precise dichotomy on the asymptotic behavior of the resetting function $r$ to determine whether $E_0^{(r)}T_a$ is finite or infinite. We show generically that if $r(x)$ is on the order $|x|^{2l}$, with $l>-1$, then $\log E_0^{(r)}T_a$ is on the order $|a|^{l+1}$; in particular, the smaller the asymptotic size of $r$, the smaller the asymptotic growth rate of $E_0^{(r)}T_a$. The asymptotic growth rate of $E_0^{(r)}T_a$ continues to decrease when $r(x)\sim \frac{D\lambda}{x^2}$ with $\lambda>1$; now the growth rate of $E_0^{(r)}T_a$ is more or less on the order $|a|^{\frac{1+\sqrt{1+8\lambda}}2}$. However, if $\lambda=1$, then $E_0^{(r)}T_a=\infty$, for $a\neq0$.
We report on the first high frequency VLBI observations of the nearby broad absorption line quasar (BALQSO), Mrk 231. Three epochs of observations were achieved at 15 GHz and 22 GHz, two of these included 43 GHz observations as well. The nuclear radio source is resolved as a compact double. The core component experienced a strong flare in which the flux density at 22 GHz increased by $> 150%$ (45 mJy) in three months. Theoretical models of the flare imply that the emission is likely enhanced by very strong Doppler boosting of a highly relativistic ejecta with a kinetic energy flux, $Q \sim 3 \times 10^{43} \mathrm{ergs/sec}$. Combining our data with two previous epochs of 15 GHz data, shows marginal evidence for the slow advance of the secondary component (located $\approx 0.97$ pc from the core) over a 9.4 year span. We estimate that the long term time averaged kinetic energy flux of the secondary at $\bar{Q}\approx 10^{42}\mathrm{ergs/sec}$. Low frequency VLBA observations indicate that the secondary is seen through a shroud of free-free absorbing gas with an emission measure of $\approx 10^{8} \mathrm{cm}^{-6}\mathrm{pc}$. The steep spectrum secondary component appears to be a compact radio lobe that is associated with a working surface between the ram-pressure confined jet, and a dense medium that is likely to be the source of the free-free absorption. The properties of the dense gas are consistent with the temperatures, displacement from the nucleus and the column density of total hydrogen commonly associated with the BAL wind.
We show that given an ideal I generated by regular functions f_1,...,f_r on the smooth complex variety X, the Bernstein-Sato polynomial of I is equal to the reduced Bernstein-Sato polynomial of the function g=\sum_{i=1}^rf_iy_i on the product of X with an r-dimensional affine space. By combining this with results from [BMS], we relate invariants and properties of I to those of g. We also use the result on Bernstein-Sato polynomials to show that the Strong Monodromy Conjecture for Igusa zeta functions of principal ideals implies a similar statement for arbitrary ideals.
We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a transition redshift, z_tran, above which the stellar population is dominated by massive, zero-metallicity stars and below which it is dominated by a Scalo mass function; (ii) the product of the escape fraction of stellar ionizing photons from their host galaxies and the star-formation efficiency, f_esc f_*. We constrain the allowed range of these free parameters at high redshifts based on the lack of the HI Gunn-Peterson trough at z<6 and the upper limit on the total intergalactic optical depth for electron scattering, tau_es<0.18, from recent cosmic microwave background (CMB) experiments. We find that quasars ionize helium by a redshift z~4, but cannot reionize hydrogen by themselves before z~6. A major fraction of the allowed combinations of f_esc f_* and z_tran lead to an early peak in the ionized fraction due to metal-free stars at high redshifts. This sometimes results in two reionization epochs, namely an early HII or HeIII overlap phase followed by recombination and a second overlap phase. Even if early overlap is not achieved, the peak in the visibility function for scattering of the CMB often coincides with the early ionization phase rather than with the actual reionization epoch. Consequently, tau_es does not correspond directly to the reionization redshift. We generically find values of tau_es>7%, that should be detectable by the MAP satellite.
We obtain some new results concerning the small deviation problem for $S=\sum_n q^n X_n$ and $M=\sup_n q^n X_n$, where $0<q<1$ and $(X_n)$ are i.i.d. non-negative random variables. In particular, the asymptotics is shown to be the same for $S$ and $M$ in some cases.
We numerically explore how the subhalo mass-loss evolution is affected by the tidal coherences measured along different eigenvector directions. The mean virial-to-accretion mass ratios of the subhalos are used to quantify the severity of their mass-loss evolutions within the hosts, and the tidal coherence is expressed as an array of three numbers each of which quantifies the alignment between the tidal fields smoothed on the scales of $2$ and $30\,h^{-1}$Mpc in each direction of three principal axes. Using a Rockstar halo catalog retrieved from a N-body simulation, we investigate if and how the mass-loss evolutions of the subhalos hosted by distinct halos at fixed mass scale of [$1$-$3$]$10^{14}\,h^{-1}\,M_{\odot}$ are correlated with three components of the tidal coherence. The tides coherent along different eigenvector directions are found to have different effects on the subhalo mass-loss evolution, which cannot be ascribed to the differences in the densities and ellipticities of the local environments. It is shown that the substructures surrounded by the tides highly coherent along the first eigenvector direction and highly {\it incoherent} along the third eigenvector direction experience the least severe mass-loss evolution, while the tides highly {\it incoherent} only along the first eigenvector direction is responsible for the most severe mass-loss evolution of the subhalos. Explaining that the coherent tides have an obstructing effect on the satellite infalls onto their hosts and that the strength of the obstruction effect depends on which directions the tides are coherent or {\it incoherent} along, we suggest that the multidimensional dependence of the substructure evolution on the tidal coherence should be deeply related to the complex nature of the large-scale assembly bias.
An all-resonant method is proposed to control the quantum state of superconducting resonators. This approach uses a tunable artificial atom linearly coupled to resonators, and allows for efficient routes to Fock state synthesis, qudit logic operations, and synthesis of NOON states. This resonant approach is theoretically analyzed, and found to perform signficantly better than existing proposals using the same technology.
We report the identification of a new, long period detached eclipsing binary by the All-Sky Automated Survey for Supernovae (ASAS-SN). Combining V-band photometry from ASAS-SN, ASAS and KELT, we constructed a light curve spanning 2006-2018. ASASSN-V J192543.72+402619.0 is an eccentric detached eclipsing binary with an orbital period of $P\sim7.3$ yr, a minimum orbital eccentricity of $e_{min}\sim0.2$ and a primary eclipse lasting $\sim160$ d. We also detect a secondary eclipse that is $\sim 0.6$ mag shallower. Multi-band photometry suggests that the more luminous component of the binary is an M-giant. Further photometric and spectroscopic observations are encouraged.
We ask the question "when will natural selection on a gene in a spatially structured population cause a detectable trace in the patterns of genetic variation observed in the contemporary population?". We focus on the situation in which 'neighbourhood size', that is the effective local population density, is small. The genealogy relating individuals in a sample from the population is embedded in a spatial version of the ancestral selection graph and through applying a diffusive scaling to this object we show that whereas in dimensions at least three, selection is barely impeded by the spatial structure, in the most relevant dimension, $d=2$, selection must be stronger (by a factor of $\log(1/\mu)$ where $\mu$ is the neutral mutation rate) if we are to have a chance of detecting it. The case $d=1$ was handled in Etheridge et al. (2015).   The mathematical interest is that although the system of branching and coalescing lineages that forms the ancestral selection graph converges to a branching Brownian motion, this reflects a delicate balance of a branching rate that grows to infinity and the instant annullation of almost all branches through coalescence caused by the strong local competition in the population.