14,908 research outputs found
Explosive Nucleosynthesis in Axisymmetrically Deformed Type II Supernovae
Explosive nucleosynthesis under the axisymmetric explosion in Type II
supernova has been performed by means of two dimensional hydrodynamical
calculations. We have compared the results with the observations of SN 1987A.
Our chief findings are as follows: (1) is synthesized so much as to
explain the tail of the bolometric light curve of SN 1987A. We think this is
because the alpha-rich freezeout takes place more actively under the
axisymmetric explosion. (2) and tend to be overproduced
compared with the observations. However, this tendency relies strongly on the
progenitor's model.
We have also compared the abundance of each element in the mass number range
with the solar values. We have found three outstanding features. (1)
For the nuclei in the range , their abundances are insensitive to the
initial form of the shock wave. This insensitivity is favored since the
spherical calculations thus far can explain the solar system abundances in this
mass range. (2) There is an enhancement around A=45 in the axisymmetric
explosion compared with the spherical explosion fairly well. In particular,
, which is underproduced in the present spherical calculations, is
enhanced significantly. (3) In addition, there is an enhancement around A=65.
This tendency does not rely on the form of the mass cut but of the initial
shock wave. This enhancement may be the problem of the overproduction in this
mass range, although this effect would be relatively small since Type I
supernovae are chiefly responsible for this mass number range.Comment: 32 pages, 12 figures, LaTe
Birth of Closed Strings and Death of Open Strings during Tachyon Condensation
The tremendous progress achieved through the study of black holes and branes
suggests that their time dependent generalizations called Spacelike branes
(S-branes) may prove similarly useful. An example of an established approach to
S-branes is to include a string boundary interaction and we first summarize
evidence for the death of open string degrees of freedom for the homogeneous
rolling tachyon on a decaying brane. Then, we review how to extract the flat
S-brane worldvolumes describing the homogeneous rolling tachyon and how large
deformations correspond to creation of lower dimensional strings and branes.
These S-brane worldvolumes are governed by S-brane actions which are on equal
footing to D-brane actions, since they are derived by imposing conformality on
the string worldsheet, as well as by analyzing fluctuations of time dependent
tachyon configurations. As further examples we generalize previous solutions of
the S-brane actions so as to describe multiple decaying and nucleating closed
fundamental strings. Conceptually S-brane actions are therefore different from
D-brane actions and can provide a description of time dependent strings/branes
and possibly their interactions.Comment: 15 pages, 7 eps figures; invited review for Modern Physics Letters A,
including new solutions for S-brane actions. v2 published version, minor
typos correcte
Nucleus from String Theory
In generic holographic QCD, we find that baryons are bound to form a nucleus,
and that its radius obeys the empirically-known mass number (A) dependence r
A^{1/3} for large A. Our result is robust, since we use only a generic property
of D-brane actions in string theory. We also show that nucleons are bound
completely in a finite volume. Furthermore, employing a concrete holographic
model (derived by Hashimoto, Iizuka, and Yi, describing a multi-baryon system
in the Sakai-Sugimoto model), the nuclear radius is evaluated as O(1) x A^{1/3}
[fm], which is consistent with experiments.Comment: 4 pages; Ver.2: terminology on nuclear density saturation modified, a
reference adde
Aspects of Puff Field Theory
We describe some features of the recently constructed "Puff Field Theory,"
and present arguments in favor of it being a field theory decoupled from
gravity. We construct its supergravity dual and calculate the entropy of this
theory in the limit of large 't Hooft coupling. We also determine the leading
irrelevant operator that governs its deviation from N=4 super Yang-Mills
theory.Comment: 31 pages, 1 figur
Dynamical electroweak symmetry breaking with superheavy quarks and 2+1 composite Higgs model
Recently, a new class of models describing the quark mass hierarchy has been
introduced. In this class, while the t quark plays a minor role in electroweak
symmetry breaking (EWSB), it is crucial in providing the quark mass hierarchy.
In this paper, we analyze the dynamics of a particular model in this class, in
which the b' and t' quarks of the fourth family are mostly responsible for
dynamical EWSB. The low energy effective theory in this model is derived. It
has a clear signature, a 2 + 1 structure of composite Higgs doublets: two
nearly degenerate \Phi_{b'} and \Phi_{t'}, and a heavier top-Higgs resonance
\Phi_t \sim \bar{t}_{R}(t,b)_L. The properties of these composites are
described in detail, and it is shown that the model satisfies the electroweak
precision data constraints. The signatures of these composites at the Large
Hadron Collider are briefly discussed.Comment: 17 pages, 3 figures; v.2: references and clarifications added: PRD
versio
A Matrix Model for Baryons and Nuclear Forces
We propose a new matrix model describing multi-baryon systems. We derive the
action from open string theory on the wrapped baryon vertex D-branes embedded
in the D4-D8 model of large N holographic QCD. The positions of k baryons are
unified into k x k matrices, with spin/isospin of the baryons encoded in a set
of k-vectors. Holographic baryons are known to be very small in the large 't
Hooft coupling limit, and our model offers a better systematic approach to
dynamics of such baryons at short distances. We compute energetics and spectra
(k=1), and also short-distance nuclear force (k=2). In particular, we obtain a
new size of the holographic baryon and find a precise form of the repulsive
core of nucleons. This matrix model complements the instanton soliton picture
of holographic baryons, whose small size turned out to be well below the
natural length scale of the approximation involved there. Our results show
that, nevertheless, the basic properties of holographic baryons obtained there
are robust under stringy corrections within a few percents.Comment: 30 pages. v3: more comments added, published versio
Holographic Nuclei : Supersymmetric Examples
We provide a dual gravity description of a supersymmetric heavy nucleus,
following the idea of our previous paper arXiv:0809.3141. The supersymmetric
nucleus consists of a merginal bound state of baryons distributed over a
ball in 3 dimensions. In the gauge/string duality, the baryon in N=4 super
Yang-Mills (SYM) theory corresponds to a D5-brane wrapping S^5 of the AdS_5 x
S^5 spacetime, so the nucleus corresponds to a collection of D5-branes. We
take a large and a near horizon limits of a back-reacted geometry generated
by the wrapped D5-branes, where we find a gap in the supergravity
fluctuation spectrum. This spectrum is a gravity dual of giant resonances of
heavy nuclei, in the supersymmetric toy example of QCD.Comment: 9 pages, 6 figures; v2:a refernce adde
Stringy Derivation of Nahm Construction of Monopoles
We derive the Nahm construction of monopoles from exact tachyon condensation
on unstable D-branes. The Dirac operator used in the Nahm construction is
identified with the tachyon profile in our D-brane approach, and we provide
physical interpretation of the procedures Nahm gave. Crucial is the
introduction of infinite number of brane-antibranes from which arbitrary
D-brane can be constrcuted, exhibitting a unified view of various D-branes. We
explicitly show the equivalence of the D3-brane boundary state with the
monopole profile and the D1-brane boundary state with the Nahm data as
transverse scalars.Comment: 18 pages, 4 eps figures, JHEP style, comments about low energy limits
added, references adde
Computing topological invariants with one and two-matrix models
A generalization of the Kontsevich Airy-model allows one to compute the
intersection numbers of the moduli space of p-spin curves. These models are
deduced from averages of characteristic polynomials over Gaussian ensembles of
random matrices in an external matrix source. After use of a duality, and of an
appropriate tuning of the source, we obtain in a double scaling limit these
intersection numbers as polynomials in p. One can then take the limit p to -1
which yields a matrix model for orbifold Euler characteristics. The
generalization to a time-dependent matrix model, which is equivalent to a
two-matrix model, may be treated along the same lines ; it also yields a
logarithmic potential with additional vertices for general p.Comment: 30 pages, added references, changed conten
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