29,441 research outputs found
Machine Learning Cosmic Expansion History
We use the machine learning techniques, for the first time, to study the
background evolution of the universe in light of 30 cosmic chronometers. From 7
machine learning algorithms, using the principle of mean squared error
minimization on testing set, we find that Bayesian ridge regression is the
optimal method to extract the information from cosmic chronometers. By use of a
power-law polynomial expansion, we obtain the first Hubble constant estimation
km s Mpc from machine learning. From
the view of machine learning, we may rule out a large number of cosmological
models, the number of physical parameters of which containing is larger
than 3. Very importantly and interestingly, we find that the parameter spaces
of 3 specific cosmological models can all be clearly compressed by considering
both their explanation and generalization abilities.Comment: 4.5 pages, 7 figures. This is the first work using machine learning
algorithms to study the dark energ
Cosmological implications of Fast Radio Burst / Gamma-Ray Burst Associations
If a small fraction of Fast Radio Bursts (FRBs) are associated with Gamma-Ray
Bursts (GRBs), as recently suggested by Zhang, the combination of redshift
measurements of GRBs and dispersion measure (DM) measurements of FRBs opens a
new window to study cosmology. At where the universe is essentially fully
ionized, detections of FRB/GRB pairs can give an independent measurement of the
intergalactic medium portion of the baryon mass fraction, , of the universe. If a good sample of FRB/GRB associations are discovered
at higher redshifts, the free electron column density history can be mapped,
which can be used to probe the reionization history of both hydrogen and helium
in the universe. We apply our formulation to GRBs 101011A and 100704A that each
might have an associated FRB, and constrained to be
consistent with the value derived from other methods. The methodology developed
here is also applicable, if the redshifts of FRBs not associated with GRBs can
be measured by other means.Comment: 5 pages, 2 figures, 1 table, Accepted by ApJ
Supervised Learning Based Online Tracking Filters: An XGBoost Implementation
The target state filter is an important module in the traditional target
tracking framework. In order to get satisfactory tracking results, traditional
Bayesian methods usually need accurate motion models, which require the
complicated prior information and parameter estimation. Therefore, the modeling
process has a key impact on traditional Bayesian filters for target tracking.
However, when encountering unknown prior information or the complicated
environment, traditional Bayesian filters have the limitation of greatly
reduced accuracy. In this paper, we propose a supervised learning based online
tracking filter(SLF). First, a complete tracking filter framework based on
supervised learning is established, which is directly based on data-driven and
establishes the mapping relationship between data. In other words, the proposed
filter does not require the prior information about target dynamics and clutter
distribution. Then, an implementation based on eXtreme Gradient Boosting
(XGBoost) is provided, which proves the portability and applicability of the
SLF framework. Meanwhile, the proposed framework will encourage other
researchers to continue to expand the field of combining traditional filters
with supervised learning. Finally, numerical simulation experiments prove the
effectiveness of the proposed filter
Tuning Feshbach resonance in cold atomic gases with inter-channel coupling
We show that the essential properties of a Feshbach resonance in cold atomic
gases can be tuned by dressing the atomic states in different scattering
channels through inter-channel couplings. Such a scheme can be readily
implemented in the orbital Feshbach resonance of alkaline-earth-like atoms by
coupling hyperfine states in the clock-state manifolds. Using Yb atoms
as an example, we find that both the resonance position and the two-body
bound-state energy depend sensitively on the inter-channel coupling strength,
which offers control parameters in tuning the inter-atomic interactions. We
also demonstrate the dramatic impact of the dressed Feshbach resonance on
many-body processes such as the polaron to molecule transition and the BCS-BEC
crossover.Comment: 6 pages, 4 figure
Meson Decays in an Extended Nambu--Jona-Lasinio model with Heavy Quark Flavors
In a previous work, we proposed an extended Nambu--Jona-Lasinio (NJL) model
including heavy quark flavors. In this work, we will calculate strong and
radiative decays of vector mesons in this extended NJL model, including light
, , , and heavy , , ,
Non-Bloch topological invariants in a non-Hermitian domain-wall system
We study non-Bloch bulk-boundary correspondence in a non-Hermitian
Su-Schieffer-Heeger model in a domain-wall configuration where the left and
right bulks have different parameters. Focusing on the case where chiral
symmetry is still conserved, we show that non-Hermitian skin effects of bulk
states persist in the system, while the definition of the non-Bloch winding
number of either bulk depends on parameters on both sides of the boundary.
Under these redefined non-Bloch topological invariants, we confirm non-Bloch
bulk-boundary correspondence under the domain-wall configuration, which
exemplifies the impact of boundary conditions in non-Hermitian topological
systems.Comment: 9 pages, 6 figure
Testing the Cosmic Anisotropy with Supernovae Data: Hemisphere Comparison and Dipole Fitting
The cosmological principle is one of the cornerstones in modern cosmology. It
assumes that the universe is homogeneous and isotropic on cosmic scales. Both
the homogeneity and the isotropy of the universe should be tested carefully. In
the present work, we are interested in probing the possible preferred direction
in the distribution of type Ia supernovae (SNIa). To our best knowledge, two
main methods have been used in almost all of the relevant works in the
literature, namely the hemisphere comparison (HC) method and the dipole fitting
(DF) method. However, the results from these two methods are not always
approximately coincident with each other. In this work, we test the cosmic
anisotropy by using these two methods with the Joint Light-Curve Analysis (JLA)
and simulated SNIa datasets. In many cases, both methods work well, and their
results are consistent with each other. However, in the cases with two (or even
more) preferred directions, the DF method fails while the HC method still works
well. This might shed new light on our understanding of these two methods.Comment: 18 pages, 10 figures, 1 table, revtex4; v2: title changed,
discussions added, Phys. Rev. D in press; v3: published versio
Universal quantum gates on electron-spin qubits with quantum dots inside single-side optical microcavities
We present some compact quantum circuits for a deterministic quantum
computing on electron-spin qubits assisted by quantum dots inside single-side
optical microcavities, including the CNOT, Toffoli, and Fredkin gates. They are
constructed by exploiting the giant optical Faraday rotation induced by a
single-electron spin in a quantum dot inside a single-side optical microcavity
as a result of cavity quantum electrodynamics. Our universal quantum gates have
some advantages. First, all the gates are accomplished with a success
probability of 100% in principle. Second, our schemes require no additional
electron-spin qubits and they are achieved by some input-output processes of a
single photon. Third, our circuits for these gates are simple and economic.
Moreover, our devices for these gates work in both the weak coupling and the
strong coupling regimes, and they are feasible in experiment.Comment: 13 pages, 6 figures, a single column. The negligible error on the
schematic figures for some PBSs in Opt. Express 22, 593-607 (2014) is
correcte
Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities
Quantum logic gates are the key elements in quantum computing. Here we
investigate the possibility of achieving a scalable and compact quantum
computing based on stationary electron-spin qubits, by using the giant optical
circular birefringence induced by quantum-dot spins in double-sided optical
microcavities as a result of cavity quantum electrodynamics. We design the
compact quantum circuits for implementing universal and deterministic quantum
gates for electron-spin systems, including the two-qubit CNOT gate and the
three-qubit Toffoli gate. They are compact and economic, and they do not
require additional electron-spin qubits. Moreover, our devices have good
scalability and are attractive as they both are based on solid-state quantum
systems and the qubits are stationary. They are feasible with the current
experimental technology, and both high fidelity and high efficiency can be
achieved when the ratio of the side leakage to the cavity decay is low.Comment: 12 pages, 5 figures, one colum
Vorticity in Heavy-Ion Collisions
We study the event-by-event generation of flow vorticity in RHIC Au + Au
collisions and LHC Pb + Pb collisions by using the HIJING model. Different
definitions of the vorticity field and velocity field are considered. A variety
of properties of the vorticity are explored, including the impact parameter
dependence, the collision energy dependence, the spatial distribution, the
event-by-event fluctuation of the magnitude and azimuthal direction, and the
time evolution. In addition, the spatial distribution of the flow helicity is
also studied.Comment: V2: 31 pages, 16 figures; new discussion added to the end of Sec.VI,
references update
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