20,423 research outputs found
Asymptotic correlation functions and FFLO signature for the one-dimensional attractive Hubbard model
We study the long-distance asymptotic behavior of various correlation
functions for the one-dimensional (1D) attractive Hubbard model in a partially
polarized phase through the Bethe ansatz and conformal field theory approaches.
We particularly find the oscillating behavior of these correlation functions
with spatial power-law decay, of which the pair (spin) correlation function
oscillates with a frequency (). Here is the mismatch in the Fermi surfaces of
spin-up and spin-down particles. Consequently, the pair correlation function in
momentum space has peaks at the mismatch , which has been
observed in recent numerical work on this model. These singular peaks in
momentum space together with the spatial oscillation suggest an analog of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in the 1D Hubbard model. The
parameter representing the lattice effect becomes prominent in critical
exponents which determine the power-law decay of all correlation functions. We
point out that the backscattering of unpaired fermions and bound pairs within
their own Fermi points gives a microscopic origin of the FFLO pairing in 1D.Comment: 26 pages, 4 figures, published version, a series of study on the 1D
attractive Hubbard model, few typos were corrected, references were added,
also see arXiv:1708.07784 and arXiv:1708.0777
NAIS: Neural Attentive Item Similarity Model for Recommendation
Item-to-item collaborative filtering (aka. item-based CF) has been long used
for building recommender systems in industrial settings, owing to its
interpretability and efficiency in real-time personalization. It builds a
user's profile as her historically interacted items, recommending new items
that are similar to the user's profile. As such, the key to an item-based CF
method is in the estimation of item similarities. Early approaches use
statistical measures such as cosine similarity and Pearson coefficient to
estimate item similarities, which are less accurate since they lack tailored
optimization for the recommendation task. In recent years, several works
attempt to learn item similarities from data, by expressing the similarity as
an underlying model and estimating model parameters by optimizing a
recommendation-aware objective function. While extensive efforts have been made
to use shallow linear models for learning item similarities, there has been
relatively less work exploring nonlinear neural network models for item-based
CF.
In this work, we propose a neural network model named Neural Attentive Item
Similarity model (NAIS) for item-based CF. The key to our design of NAIS is an
attention network, which is capable of distinguishing which historical items in
a user profile are more important for a prediction. Compared to the
state-of-the-art item-based CF method Factored Item Similarity Model (FISM),
our NAIS has stronger representation power with only a few additional
parameters brought by the attention network. Extensive experiments on two
public benchmarks demonstrate the effectiveness of NAIS. This work is the first
attempt that designs neural network models for item-based CF, opening up new
research possibilities for future developments of neural recommender systems
Custodial Symmetry Violation in Scalar Extensions of the Standard Model
The new measurement of the W boson mass from the CDF collaboration shows a
significant tension with the Standard Model prediction, which evidences
violation of custodial symmetry in the scalar sector. We study the scalar
extensions of the Standard Model, which can be categorized into two classes,
scalar sector with custodial symmetry (Georgi-Machacek model and its
generalizations) and scalar sector without custodial symmetry, and explore how
these extensions fit to the electroweak precision data and the CDF new .
The favored oblique parameters are coming from either the large mass splitting
in the multiplet via the loop contribution or the large vacuum expectation
value which breaks custodial symmetry at the tree level. In particular, we find
that GeV new particles are allowed in the scalar extension
scenarios.Comment: 24 pages, 4 figure
Genome-wide comparative analysis of metacaspases in unicellular and filamentous cyanobacteria
<p>Abstract</p> <p>Background</p> <p>Cyanobacteria are an ancient group of photoautotrophic prokaryotes with wide variations in genome size and ecological habitat. Metacaspases (MCAs) are cysteine proteinases that have sequence homology to caspases and play essential roles in programmed cell death (PCD). MCAs have been identified in several prokaryotes, fungi and plants; however, knowledge about cyanobacterial metacaspases still remains obscure. With the availability of sequenced genomes of 33 cyanobacteria, we perform a comparative analysis of metacaspases and explore their distribution, domain structure and evolution.</p> <p>Results</p> <p>A total of 58 putative MCAs were identified, which are abundant in filamentous diazotrophic cyanobacteria and <it>Acaryochloris marina </it>MBIC 11017 and absent in all <it>Prochlorococcus </it>and marine <it>Synechococcus </it>strains, except <it>Synechococcus </it>sp. PCC 7002. The Cys-His dyad of caspase superfamily is conserved, while mutations (Tyr in place of His and Ser/Asn/Gln/Gly instead of Cys) are also detected in some cyanobacteria. MCAs can be classified into two major families (α and β) based on the additional domain structure. Ten types and a total of 276 additional domains were identified, most of which involves in signal transduction. Apoptotic related NACHT domain was also found in two cyanobacterial MCAs. Phylogenetic tree of MCA catalytic P20 domains coincides well with the domain structure and the phylogenies based on 16s rRNA.</p> <p>Conclusions</p> <p>The existence and quantity of MCA genes in unicellular and filamentous cyanobacteria are a function of the genome size and ecological habitat. MCAs of family α and β seem to evolve separately and the recruitment of WD40 additional domain occurs later than the divergence of the two families. In this study, a general framework of sequence-structure-function connections for the metacaspases has been revealed, which may provide new targets for function investigation.</p
Complete EFT Operator Bases for Dark Matter and Weakly-Interacting Light Particle
The standard model can be extended to include weakly-interacting light
particle (WILP): real or complex singlet scalar, Majorana or Dirac neutral
fermion, neutral or hidden-charged vector boson, etc. Imposing the
symmetry, these particles can be lifted as the weakly-interacting massive
particle (WIMP), the candidate of dark matter. Instead, imposing the shift
symmetry on the scalar components gives rise to the axion-like particle, dark
photon, etc. Utilizing these light degree of freedom along with the standard
model particles and imposing different symmetries, we construct the complete
and independent sets of effective operators up to dimension eight with the
Young tensor technique, consistent with counting from the Hilbert series.Comment: 109 pages. arXiv admin note: text overlap with arXiv:2305.1677
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