The Experts below are selected from a list of 119472 Experts worldwide ranked by ideXlab platform
Savan Kharel - One of the best experts on this subject based on the ideXlab platform.
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study of Momentum Space scalar amplitudes in ads Spacetime
2020Co-Authors: Soner Albayrak, Chandramouli Chowdhury, Savan KharelAbstract:In this paper, we explore Momentum Space approach to computing scalar amplitudes in anti--de Sitter (AdS) Space. We show that the algorithm derived by Arkani-Hamed, Benincasa, and Postnikov for cosmological wave functions can be straightforwardly adopted for AdS transition amplitudes in Momentum Space, allowing one to bypass bulk point integrations. We demonstrate the utility of this approach in AdS by presenting several explicit results both at tree and loop level.
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towards the higher point holographic Momentum Space amplitudes part ii gravitons
2019Co-Authors: Soner Albayrak, Savan KharelAbstract:In this follow up paper, we calculate higher point tree level graviton Witten diagrams in AdS4 via bulk perturbation theory. We show that by rearranging the bulk to bulk graviton propagators, the calculations effectively reduce to the computation of a scalar factor. Analogous to the amplitudes for vector boson interactions we computed in the previous paper, scalar factors for the graviton exchange diagrams also become relatively simple when written in Momentum Space. We explicitly calculate higher point correlators and discuss how this Momentum Space formalism makes flat Space and collinear limits simpler.
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towards the higher point holographic Momentum Space amplitudes
2019Co-Authors: Soner Albayrak, Savan KharelAbstract:In this paper, we calculate higher point tree level vector amplitudes propagating in AdS_4, or equivalently the dual boundary current correlators. We use bulk perturbation theory to compute tree level Witten diagrams. We show that when these amplitudes are written in Momentum Space, they reduce to relatively simple expressions. We explicitly compute four and five point correlators and also sketch a general strategy to compute the full six-point correlators.
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towards the higher point holographic Momentum Space amplitudes
2018Co-Authors: Soner Albayrak, Savan KharelAbstract:In this paper, we calculate higher point tree level vector amplitudes propagating in AdS$_4$. We use bulk perturbation theory to compute tree level Witten diagrams. We show that when these amplitudes are written in Momentum Space, they reduce to relatively simple expressions. We explicitly compute four and five point correlators and also sketch a general strategy to compute the full six-point correlators.
Soner Albayrak - One of the best experts on this subject based on the ideXlab platform.
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study of Momentum Space scalar amplitudes in ads Spacetime
2020Co-Authors: Soner Albayrak, Chandramouli Chowdhury, Savan KharelAbstract:In this paper, we explore Momentum Space approach to computing scalar amplitudes in anti--de Sitter (AdS) Space. We show that the algorithm derived by Arkani-Hamed, Benincasa, and Postnikov for cosmological wave functions can be straightforwardly adopted for AdS transition amplitudes in Momentum Space, allowing one to bypass bulk point integrations. We demonstrate the utility of this approach in AdS by presenting several explicit results both at tree and loop level.
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towards the higher point holographic Momentum Space amplitudes part ii gravitons
2019Co-Authors: Soner Albayrak, Savan KharelAbstract:In this follow up paper, we calculate higher point tree level graviton Witten diagrams in AdS4 via bulk perturbation theory. We show that by rearranging the bulk to bulk graviton propagators, the calculations effectively reduce to the computation of a scalar factor. Analogous to the amplitudes for vector boson interactions we computed in the previous paper, scalar factors for the graviton exchange diagrams also become relatively simple when written in Momentum Space. We explicitly calculate higher point correlators and discuss how this Momentum Space formalism makes flat Space and collinear limits simpler.
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towards the higher point holographic Momentum Space amplitudes
2019Co-Authors: Soner Albayrak, Savan KharelAbstract:In this paper, we calculate higher point tree level vector amplitudes propagating in AdS_4, or equivalently the dual boundary current correlators. We use bulk perturbation theory to compute tree level Witten diagrams. We show that when these amplitudes are written in Momentum Space, they reduce to relatively simple expressions. We explicitly compute four and five point correlators and also sketch a general strategy to compute the full six-point correlators.
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towards the higher point holographic Momentum Space amplitudes
2018Co-Authors: Soner Albayrak, Savan KharelAbstract:In this paper, we calculate higher point tree level vector amplitudes propagating in AdS$_4$. We use bulk perturbation theory to compute tree level Witten diagrams. We show that when these amplitudes are written in Momentum Space, they reduce to relatively simple expressions. We explicitly compute four and five point correlators and also sketch a general strategy to compute the full six-point correlators.
Dawei Wang - One of the best experts on this subject based on the ideXlab platform.
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many body chiral edge currents and sliding phases of atomic spin waves in Momentum Space lattice
2020Co-Authors: Han Cai, Dawei Wang, Jianmin YuanAbstract:Collective excitations (spin waves) of long-lived atomic hyperfine states can be synthesized into a Bose-Hubbard model in Momentum Space. We explore many-body ground states and dynamics of a two-leg Momentum-Space lattice formed by two coupled hyperfine states. Essential ingredients of this setting are a staggered artificial magnetic field engineered by lasers that couple the spin wave states and a state-dependent long-range interaction, which is induced by laser dressing a hyperfine state to a Rydberg state. The Rydberg dressed two-body interaction gives rise to a state-dependent blockade in Momentum Space and can amplify staggered flux-induced antichiral edge currents in the many-body ground state in the presence of magnetic flux. When the Rydberg dressing is applied to both hyperfine states, exotic sliding insulating and superfluid (supersolid) phases emerge. Because of the Rydberg dressed long-range interaction, spin waves slide along a leg of the Momentum-Space lattice without costing energy. Our study paves a route to the quantum simulation of topological phases and exotic dynamics with interacting spin waves of atomic hyperfine states in Momentum-Space lattice.
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experimental observation of Momentum Space chiral edge currents in room temperature atoms
2019Co-Authors: Han Cai, Dawei Wang, Jinhong Liu, Shiyao Zhu, Junxiang ZhangAbstract:Chiral edge currents play an important role in characterizing topological matter. In atoms, they have been observed at such a low temperature that the atomic motion can be measured. Here we report the first experimental observation of chiral edge currents in atoms at room temperature. Staggered magnetic fluxes are induced by the spatial phase difference between two standing-wave light fields, which couple atoms to form a Momentum-Space zigzag superradiance lattice. The chiral edge currents are measured by comparing the directional superradiant emissions of two timed Dicke states in the lattice. Our results pave the way for simulating topological physics in hot atoms.
Lei Shi - One of the best experts on this subject based on the ideXlab platform.
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generating optical vortex beams by Momentum Space polarization vortices centred at bound states in the continuum
2020Co-Authors: Bo Wang, Yiwen Zhang, Ang Chen, Wenzhe Liu, Fang Guan, Xiaohan Liu, Maoxiong Zhao, Jiajun Wang, Lei ShiAbstract:Optical vortices, beams with spiral wavefronts and screw phase dislocations, have been attracting increasing interest in various fields. Here, we theoretically propose and experimentally realize an easy approach to generating optical vortices. We leverage the inherent Momentum-Space topological vortex-like response of polarization (strong polarization anisotropy) around bound states in the continuum of two-dimensional periodic structures, for example photonic crystal slabs, to induce Pancharatnam–Berry phases and spin–orbit interaction in the beams. This new class of optical vortex generators operates in Momentum Space, meaning that the structure is almost homogeneous without a real-Space centre. In principle, any even-order optical vortex that is a diffraction-resistant high-order quasi-Bessel beam can be achieved at any desired working wavelength. The proposed approach expands the application of bound states in the continuum and topological photonics. Optical vortices can be generated by applying the winding behaviour of resonances in the Momentum Space of a photonic crystal slab, which naturally exists and is associated with bound states in the continuum, to modify the phase front of a beam.
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generating optical vortex beams by Momentum Space polarization vortices centered at bound states in the continuum
2019Co-Authors: Bo Wang, Yiwen Zhang, Ang Chen, Wenzhe Liu, Fang Guan, Xiaohan Liu, Maoxiong Zhao, Jiajun Wang, Lei ShiAbstract:An optical vortex (OV) is a beam with spiral wave front and screw phase dislocation. This kind of beams is attracting rising interest in various fields. Here we theoretically proposed and experimentally realized a novel but easy approach to generate optical vortices. We leverage the inherent topological vortex structures of polarization around bound states in the continuum (BIC) in the Momentum Space of two dimensional periodic structures, e.g. photonic crystal slabs, to induce Pancharatnam-Berry phases to the beams. This new class of OV generators operates in the Momentum Space, meaning that there is no real-Space center of structure. Thus, not only the fabrication but also the practical alignment would be greatly simplified. Any even order of OV, which is actually a quasi-non-diffractive high-order quasi-Bessel beam, at any desired working wavelength could be achieved in principle. The proposed approach expands the application of bound states in the continuum and topological photonics.
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observation of polarization vortices in Momentum Space
2018Co-Authors: Yiwen Zhang, Ang Chen, Wenzhe Liu, Chia Wei Hsu, Bo Wang, Fang Guan, Xiaohan Liu, Lei ShiAbstract:The vortex, a fundamental topological excitation featuring the in-plane winding of a vector field, is important in various areas such as fluid dynamics, liquid crystals, and superconductors. Although commonly existing in nature, vortices were observed exclusively in real Space. Here, we experimentally observed Momentum-Space vortices as the winding of far-field polarization vectors in the first Brillouin zone of periodic plasmonic structures. Using homemade polarization-resolved Momentum-Space imaging spectroscopy, we mapped out the dispersion, lifetime, and polarization of all radiative states at the visible wavelengths. The Momentum-Space vortices were experimentally identified by their winding patterns in the polarization-resolved isofrequency contours and their diverging radiative quality factors. Such polarization vortices can exist robustly on any periodic systems of vectorial fields, while they are not captured by the existing topological band theory developed for scalar fields. Our work provides a new way for designing high-$Q$ plasmonic resonances, generating vector beams, and studying topological photonics in the Momentum Space.
Matthias Neubert - One of the best experts on this subject based on the ideXlab platform.
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factorization and Momentum Space resummation in deep inelastic scattering
2007Co-Authors: Thomas Becher, Matthias Neubert, Ben D PecjakAbstract:Renormalization-group methods in soft-collinear effective theory are used to perform the resummation of large perturbative logarithms for deep-inelastic scattering in the threshold region x {yields} 1. The factorization theorem for the structure function F{sub 2}(x,Q{sup 2}) for x {yields} 1 is rederived in the effective theory, whereby contributions from the hard scale Q{sup 2} and the jet scale Q{sup 2}(1 - x) are encoded in Wilson coefficients of effective-theory operators. Resummation is achieved by solving the evolution equations for these operators. Simple analytic results for the resummed expressions are obtained directly in Momentum Space, and are free of the Landau-pole singularities inherent to the traditional moment-Space results. We show analytically that the two methods are nonetheless equivalent order by order in the perturbative expansion, and perform a numerical comparison up to next-to-next-to-leading order in renormalization-group improved perturbation theory.
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threshold resummation in Momentum Space from effective field theory
2006Co-Authors: Thomas Becher, Matthias NeubertAbstract:Methods from soft-collinear effective theory are used to perform the threshold resummation of Sudakov logarithms for the deep-inelastic structure function ${F}_{2}(x,{Q}^{2})$ in the end-point region $x\ensuremath{\rightarrow}1$ directly in Momentum Space. An explicit all-order formula is derived, which expresses the short-distance coefficient function $C$ in the convolution ${F}_{2}=C\ensuremath{\bigotimes}{\ensuremath{\phi}}_{q}$ in terms of Wilson coefficients and anomalous dimensions defined in the effective theory. Contributions associated with the physical scales ${Q}^{2}$ and ${Q}^{2}(1\ensuremath{-}x)$ are separated from nonperturbative hadronic physics in a transparent way. A crucial ingredient to the Momentum-Space resummation is the exact solution to the integro-differential evolution equation for the jet function, which is derived. The methods developed in this Letter can be applied to many other hard QCD processes.
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factorization and Momentum Space resummation in deep inelastic scattering
2006Co-Authors: Thomas Becher, Matthias Neubert, Ben D PecjakAbstract:Renormalization-group methods in soft-collinear effective theory are used to perform the resummation of large perturbative logarithms for deep-inelastic scattering in the threshold region x->1. The factorization theorem for the structure function F_2(x,Q^2) for x->1 is rederived in the effective theory, whereby contributions from the hard scale Q^2 and the jet scale Q^2(1-x) are encoded in Wilson coefficients of effective-theory operators. Resummation is achieved by solving the evolution equations for these operators. Simple analytic results for the resummed expressions are obtained directly in Momentum Space, and are free of the Landau-pole singularities inherent to the traditional moment-Space results. We show analytically that the two methods are nonetheless equivalent order by order in the perturbative expansion, and perform a numerical comparison up to next-to-next-to-leading order in renormalization-group improved perturbation theory.
