4,719 research outputs found
Big Rip in SO(1,1) phantom universe
For the inverse linear potential, the SO(1,1) field behaves as phantom for
late time and the Big Rip will occur. The field approaches zero as time
approaches the Big Rip, here. For this potential the phantom equation of state
takes the late-time minimum . We give some discussions that the Big
Rip in the SO(1,1) model may be treated as either the transition point of
universe from expansion to extract phase or the final state. In the latter
picture of the universe, the field has the symmetry and the scale factor
possesses the symmetry, for which the SO(1,1) charge plays a
crucial role.Comment: 10 pages, 1 figur
Critical state of phantom universe
The late-time evolution behavior of the autonomous system in the SO(1,1) dark
energy model with power-law potential is studied. Big Rip may be a critical
point of the autonomous system. This means that such a Big Rip may be
considered as the middle state between the expanding and contracting phases of
phantom universe. This result is also valid for some special interactions
between matter and dark energy.Comment: 6 pages, revtex
Vertex Operators of Open String States in the Intersecting D-brane World
Starting with a new bosonization scheme for the \beta\gamma CFT of the
super-conformal ghosts, vertex operators are constructed for massless open
string states in the intersecting D-brane world. These vertex operators satisfy
all requirements for a consistent RNS formulation of superstring theories, so
GSO projections can be properly taken.Comment: 4 pages, RevTe
Teleparallel Gravity in Five Dimensional Theories
We study teleparallel gravity in five-dimensional spacetime with particular
discussions on Kaluza-Klein (KK) and braneworld theories. We directly perform
the dimensional reduction by differential forms. In the braneworld theory, the
teleparallel gravity formalism in the Friedmann-Lema\^{i}tre-Robertson-Walker
cosmology is equivalent to GR due to the same Friedmann equation, whereas in
the KK case the reduction of our formulation does not recover the effect as GR
of 4-dimensional spacetime.Comment: 12 pages, no figure, revised version accepted for publication in CQ
Fidelity mechanics: analogues of the four thermodynamic laws and Landauer's principle
Fidelity mechanics is formalized as a framework to investigate quantum
critical phenomena in quantum many-body systems. This is achieved by
introducing fidelity temperature to properly quantify quantum fluctuations,
which, together with fidelity entropy and fidelity internal energy, constitute
three basic state functions in fidelity mechanics, thus enabling us to
formulate analogues of the four thermodynamic laws and Landauer's principle at
zero temperature. Fidelity flows are defined and may be interpreted as an
alternative form of renormalization group flows. Thus, both stable and unstable
fixed points are characterized in terms of fidelity temperature and fidelity
entropy: divergent fidelity temperature for unstable fixed points and zero
fidelity temperature and (locally) maximal fidelity entropy for stable fixed
points. In addition, an inherently fundamental role of duality is clarified,
resulting in a canonical form of the Hamiltonian in fidelity mechanics.
Dualities, together with symmetry groups and factorizing fields, impose the
constraints on a fidelity mechanical system, thus shaping fidelity flows from
an unstable fixed point to a stable fixed point.
A detailed analysis of fidelity mechanical state functions is presented for
the quantum XY model, the transverse field quantum Ising chain in a
longitudinal field, the spin- XYZ model and the XXZ model in a magnetic
field.Comment: 56 pages, 23 figures and 2 table
The power-law expansion universe and dark energy evolution
In order to depict the transition from deceleration to acceleration expansion
of the universe we use a power-law expansion scale factor, , with , and three parameters determined by ,
and . For the spatially flat, isotropic and homogeneous universe,
such a scale factor leads to the results that the dark energy density is slowly
changing currently, and predicts the equation of state changes from
to .Comment: 10 pages, 2 figure
The power-law expansion universe and the late-time behavior
Using the SNe Ia data we determine the three parameters in the power-law
expanding universe model with time-dependent power \cite{W}. Inputting
and , then we find the evolution curve with and
can fit very well to that from SNe observation data. The model
predicts the transition redshift . The dark energy deduced from
this model have phantom property but the universe doesn't encounter the Big Rip
singularity. Assuming that this model with the three parameters is valid for
the future universe, then we predict that the total energy density of the
universe is decreasing and will soon reach its minimum.Comment: 10 pages, 5 figure
Extended complex scalar field as quintessence
In this paper, we show the possibility that an extended complex scalar field
can be considered as an extended complex quintessence. For this model, we
derive the basic equations with a parameter which govern the evolution
of the Universe. Our model may contain a complex quintessence model for and a real quitessence model for .Comment: 8 pages. to appear in Grav. & Cosmolog
On the integrable inhomogeneous Myrzakulov I equation
By using the prolongation structure theory proposed by Morris, we give a
(2+1)-dimensional integrable inhomogeneous Heisenberg Ferromagnet models,
namely, the inhomogeneous Myrzakulov I equation. Through the motion of space
curves endowed with an additional spatial variable, its geometrical equivalent
counterpart is also presented.Comment: 7 page
Behavior Sequence Transformer for E-commerce Recommendation in Alibaba
Deep learning based methods have been widely used in industrial
recommendation systems (RSs). Previous works adopt an Embedding&MLP paradigm:
raw features are embedded into low-dimensional vectors, which are then fed on
to MLP for final recommendations. However, most of these works just concatenate
different features, ignoring the sequential nature of users' behaviors. In this
paper, we propose to use the powerful Transformer model to capture the
sequential signals underlying users' behavior sequences for recommendation in
Alibaba. Experimental results demonstrate the superiority of the proposed
model, which is then deployed online at Taobao and obtain significant
improvements in online Click-Through-Rate (CTR) comparing to two baselines.Comment: 4 pages, 1 figur
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