66,590 research outputs found
Helium star evolutionary channel to super-Chandrasekhar mass type Ia supernovae
Recent discovery of several overluminous type Ia supernovae (SNe Ia)
indicates that the explosive masses of white dwarfs may significantly exceed
the canonical Chandrasekhar mass limit. Rapid differential rotation may support
these massive white dwarfs. Based on the single-degenerate scenario, and
assuming that the white dwarfs would differentially rotate when the accretion
rate , employing Eggleton's
stellar evolution code we have performed the numerical calculations for
1000 binary systems consisting of a He star and a CO white dwarf (WD). We
present the initial parameters in the orbital period - helium star mass plane
(for WD masses of and , respectively), which
lead to super-Chandrasekhar mass SNe Ia. Our results indicate that, for an
initial massive WD of , a large number of SNe Ia may result from
super-Chandrasekhar mass WDs, and the highest mass of the WD at the moment of
SNe Ia explosion is 1.81 , but very massive () WDs
cannot be formed. However, when the initial mass of WDs is , the
explosive masses of SNe Ia are nearly uniform, which is consistent with the
rareness of super-Chandrasekhar mass SNe Ia in observations.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
A bijection between unicellular and bicellular maps
In this paper we present a combinatorial proof of a relation between the
generating functions of unicellular and bicellular maps. This relation is a
consequence of the Schwinger-Dyson equation of matrix theory. Alternatively it
can be proved using representation theory of the symmetric group. Here we give
a bijective proof by rewiring unicellular maps of topological genus
into bicellular maps of genus and pairs of unicellular maps of lower
topological genera. Our result has immediate consequences for the folding of
RNA interaction structures, since the time complexity of folding the
transformed structure is , where are the lengths of the
respective backbones, while the folding of the original structure has
time complexity, where is the length of the longer sequence.Comment: 18 pages, 13 figure
A n-qubit controlled phase gate with superconducting quantum interference devices coupled to a resonator
We present a way to realize a -qubit controlled phase gate with
superconducting quantum interference devices (SQUIDs) by coupling them to a
superconducting resonator. In this proposal, the two logical states of a qubit
are represented by the two lowest levels of a SQUID. An intermediate level of
each SQUID is utilized to facilitate coherent control and manipulation of
quantum states of the qubits. It is interesting to note that a -qubit
controlled phase gate can be achieved with SQUIDs by successively applying
a Jaynes-Cummings pulse to each of the control SQUIDs before and
after a Jaynes-Cummings pulse on the target SQUID.Comment: 9 pages, 4 figures, 1 table, RevTeX, Resubmitted to Phys. Rev.
Commuting Simplicity and Closure Constraints for 4D Spin Foam Models
Spin Foam Models are supposed to be discretised path integrals for quantum
gravity constructed from the Plebanski-Holst action. The reason for there being
several models currently under consideration is that no consensus has been
reached for how to implement the simplicity constraints. Indeed, none of these
models strictly follows from the original path integral with commuting B
fields, rather, by some non standard manipulations one always ends up with non
commuting B fields and the simplicity constraints become in fact anomalous
which is the source for there being several inequivalent strategies to
circumvent the associated problems. In this article, we construct a new
Euclidian Spin Foam Model which is constructed by standard methods from the
Plebanski-Holst path integral with commuting B fields discretised on a 4D
simplicial complex. The resulting model differs from the current ones in
several aspects, one of them being that the closure constraint needs special
care. Only when dropping the closure constraint by hand and only in the large
spin limit can the vertex amplitudes of this model be related to those of the
FK Model but even then the face and edge amplitude differ. Curiously, an ad hoc
non-commutative deformation of the variables leads from our new model
to the Barrett-Crane Model in the case of Barbero-Immirzi parameter goes to
infinity.Comment: 41 pages, 4 figure
Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Lorentzian Theory
The present paper studies the large-j asymptotics of the Lorentzian EPRL
spinfoam amplitude on a 4d simplicial complex with an arbitrary number of
simplices. The asymptotics of the spinfoam amplitude is determined by the
critical configurations. Here we show that, given a critical configuration in
general, there exists a partition of the simplicial complex into three type of
regions R_{Nondeg}, R_{Deg-A}, R_{Deg-B}, where the three regions are
simplicial sub-complexes with boundaries. The critical configuration implies
different types of geometries in different types of regions, i.e. (1) the
critical configuration restricted into R_{Nondeg} is degenerate of type-A in our definition of degeneracy, but implies
a nondegenerate discrete Euclidean geometry on R_{Deg-A}, (3) the critical
configuration restricted into R_{Deg-B} is degenerate of type-B, and implies a
vector geometry on R_{Deg-B}. With the critical configuration, we further make
a subdivision of the regions R_{Nondeg} and R_{Deg-A} into sub-complexes (with
boundary) according to their Lorentzian/Euclidean oriented 4-simplex volume
V_4(v), such that sgn(V_4(v)) is a constant sign on each sub-complex. Then in
the each sub-complex, the spinfoam amplitude at the critical configuration
gives the Regge action in Lorentzian or Euclidean signature respectively on
R_{Nondeg} or R_{Deg-A}. The Regge action reproduced here contains a sign
factor sgn(V_4(v)) of the oriented 4-simplex volume. Therefore the Regge action
reproduced here can be viewed a discretized Palatini action with on-shell
connection. Finally the asymptotic formula of the spinfoam amplitude is given
by a sum of the amplitudes evaluated at all possible critical configurations,
which are the products of the amplitudes associated to different type of
geometries.Comment: 54 pages, 2 figures, reference adde
Post-Newtonian gravitational radiation and equations of motion via direct integration of the relaxed Einstein equations. IV. Radiation reaction for binary systems with spin-spin coupling
Using post-Newtonian equations of motion for fluid bodies that include
radiation-reaction terms at 2.5 and 3.5 post-Newtonian (PN) order O[(v/c)^5]
and O[(v/c)^7] beyond Newtonian order), we derive the equations of motion for
binary systems with spinning bodies, including spin-spin effects. In particular
we determine the effects of radiation-reaction coupled to spin-spin effects on
the two-body equations of motion, and on the evolution of the spins. We find
that radiation damping causes a 3.5PN order, spin-spin induced precession of
the individual spins. This contrasts with the case of spin-orbit coupling,
where there is no effect on the spins at 3.5PN order. Employing the equations
of motion and of spin precession, we verify that the loss of total energy and
total angular momentum induced by spin-spin effects precisely balances the
radiative flux of those quantities calculated by Kidder et al.Comment: 10 pages, coincides with published versio
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