144 research outputs found
The 95zr(n, gamma)96zr cross section from the surrogate ratio method and its effect on the s-process nucleosynthesis
The 95Zr(n,gamma)96Zr reaction cross section is crucial in the modelling of
s-process nucleosynthesis in asymptotic giant branch stars because it controls
the operation of the branching point at the unstable 95Zr and the subsequent
production of 96Zr. We have carried out the measurement of the 94Zr(18O,16O)
and 90Zr(18O,16O) reactions and obtained the gamma-decay probability ratio of
96Zr* and 92Zr* to determine the 95Zr(n,gamma)96Zr reaction cross sections with
the surrogate ratio method. Our deduced maxwellian-averaged cross section of
66+-16 mb at 30 keV is close to the value recommended by Bao et al. (2000), but
30% and more than a factor of two larger than the values proposed by Toukan &
Kappeler (1990) and Lugaro et al. (2014), respectively, and routinely used in
s-process models. We tested the new rate in stellar models with masses between
2 and 6 Msun and metallicities 0.014 and 0.03. The largest changes - up 80%
variations in 96Zr - are seen in models of mass 3-4 Msun, where the 22Ne
neutron source is mildly activated. The new rate can still provide a match to
data from meteoritic stardust silicon carbide grains, provided the maximum mass
of the parent stars is below 4 Msun, for a metallicity of 0.03.Comment: 10 pages, 6 figures, accepted for publication in Ap
The gravity duals of SO/USp superconformal quivers
We study the gravity duals of SO/USp superconformal quiver gauge theories
realized by M5-branes wrapping on a Riemann surface ("G-curve") together with a
Z_2-quotient. When the G-curve has no punctures, the gravity solutions are
classified by the genus g of the G-curve and the torsion part of the four-form
flux G_4. We also find that there is an interesting relation between anomaly
contributions from two mysterious theories: T_{SO(2N)} theory with SO(2N)^3
flavor symmetry and \tilde{T}_{SO(2N)} theory with SO(2N) x USp(2N-2)^2 flavor
symmetry. The dual gravity solutions for various SO/USp-type tails are also
studied.Comment: 27 pages, 13 figures; v2 minor corrections, typos corrected, Figure
13 replaced, references adde
Fission fragments mass distributions of nuclei populated by the multinucleon transfer channels of the 18O + 232Th reaction
It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the 18O + 232Th reaction are used to study fission of fourteen nuclei 231,232,233,234Th, 232,233,234,235,236Pa, and 234,235,236,237,238U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of 231,234Th and 234,235,236Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuation–dissipation model
On 4d rank-one N=3 superconformal field theories
We study the properties of 4d N=3 superconformal field theories whose rank is
one, i.e. those that reduce to a single vector multiplet on their moduli space
of vacua. We find that the moduli space can only be of the form C^3/Z_k for
k=1,2,3,4,6, and that the supersymmetry automatically enhances to N=4 for
k=1,2. In addition, we determine the central charges a and c in terms of k, and
construct the associated 2d chiral algebras, which turn out to be exotic N=2
supersymmetric W-algebras.Comment: 24 page
Argyres-Douglas theories and S-duality
This article is distributed under the terms of the Creative Commons
Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are creditedM.B. and T.N. are partly supported by the U.S. Department of Energy under grants DOE-SC0010008, DOE-ARRA-SC0003883, and DOE-DE-SC0007897.
This research was supported in part by the National Science Foundation under Grant No.
NSF PHY11-25915. S.G. is partially supported by the ERC Advanced Grant “SyDuGraM”,
by FNRS-Belgium (convention FRFC PDR T.1025.14 and convention IISN 4.4514.08) and by the “Communaut´e Francaise de Belgique” through the ARC progra
Wall-Crossing from Boltzmann Black Hole Halos
A key question in the study of N=2 supersymmetric string or field theories is
to understand the decay of BPS bound states across walls of marginal stability
in the space of parameters or vacua. By representing the potentially unstable
bound states as multi-centered black hole solutions in N=2 supergravity, we
provide two fully general and explicit formulae for the change in the (refined)
index across the wall. The first, "Higgs branch" formula relies on Reineke's
results for invariants of quivers without oriented loops, specialized to the
Abelian case. The second, "Coulomb branch" formula results from evaluating the
symplectic volume of the classical phase space of multi-centered solutions by
localization. We provide extensive evidence that these new formulae agree with
each other and with the mathematical results of Kontsevich and Soibelman (KS)
and Joyce and Song (JS). The main physical insight behind our results is that
the Bose-Fermi statistics of individual black holes participating in the bound
state can be traded for Maxwell-Boltzmann statistics, provided the (integer)
index \Omega(\gamma) of the internal degrees of freedom carried by each black
hole is replaced by an effective (rational) index \bar\Omega(\gamma)=
\sum_{m|\gamma} \Omega(\gamma/m)/m^2. A similar map also exists for the refined
index. This observation provides a physical rationale for the appearance of the
rational Donaldson-Thomas invariant \bar\Omega(\gamma) in the works of KS and
JS. The simplicity of the wall crossing formula for rational invariants allows
us to generalize the "semi-primitive wall-crossing formula" to arbitrary decays
of the type \gamma\to M\gamma_1+N\gamma_2 with M=2,3.Comment: 71 pages, 1 figure; v3: changed normalisation of symplectic form
3.22, corrected 3.35, other cosmetic change
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