1,211 research outputs found
Quantum wire junctions breaking time reversal invariance
We explore the possibility to break time reversal invariance at the junction
of quantum wires. The universal features in the bulk of the wires are described
by the anyon Luttinger liquid. A simple necessary and sufficient condition for
the breaking of time reversal invariance is formulated in terms of the
scattering matrix at the junction. The phase diagram of a junction with generic
number of wires is investigated in this framework. We give an explicit
classification of those critical points which can be reached by bosonization
and study the interplay between their stability and symmetry content.Comment: Extended version (Appendices C and D and some references added, typos
corrected) to appear in Phys. Rev.
Quantum field theory on quantum graphs and application to their conductance
We construct a bosonic quantum field on a general quantum graph. Consistency
of the construction leads to the calculation of the total scattering matrix of
the graph. This matrix is equivalent to the one already proposed using
generalized star product approach. We give several examples and show how they
generalize some of the scattering matrices computed in the mathematical or
condensed matter physics litterature.
Then, we apply the construction for the calculation of the conductance of
graphs, within a small distance approximation. The consistency of the
approximation is proved by direct comparison with the exact calculation for the
`tadpole' graph.Comment: 32 pages; misprints in tree graph corrected; proofs of consistency
and unitarity adde
Potassium: a new actor on the globular cluster chemical evolution stage. The case of NGC 2808
We derive [K/Fe] abundance ratios for 119 stars in the globular cluster NGC
2808, all of them having O, Na, Mg and Al abundances homogeneously measured in
previous works. We detect an intrinsic star-to-star spread in the Potassium
abundance. Moreover [K/Fe] abundance ratios display statistically significant
correlations with [Na/Fe] and [Al/Fe], and anti-correlations with [O/Fe] and
[Mg/Fe]. All the four Mg deficient stars ([Mg/Fe]<0.0) discovered so far in NGC
2808 are enriched in K by ~0.3 dex with respect to those with normal [Mg/Fe].
NGC 2808 is the second globular cluster, after NGC 2419, where a clear Mg-K
anti-correlation is detected, albeit of weaker amplitude. The simultaneous
correlation/anti-correlation of [K/Fe] with all the light elements usually
involved in the chemical anomalies observed in globular cluster stars, strongly
support the idea that these abundance patterns are due to the same
self-enrichment mechanism that produces Na-O and Mg-Al anti-correlations. This
finding suggests that detectable spreads in K abundances may be typical in the
massive globular clusters where the self-enrichment processes are observed to
produce their most extreme manifestations.Comment: Accepted for publication by ApJ, 5 pages, 3 figure
Junctions of anyonic Luttinger wires
We present an extended study of anyonic Luttinger liquids wires jointing at a
single point. The model on the full line is solved with bosonization and the
junction of an arbitrary number of wires is treated imposing boundary
conditions that preserve exact solvability in the bosonic language. This allows
to reach, in the low momentum regime, some of the critical fixed points found
with the electronic boundary conditions. The stability of all the fixed points
is discussed.Comment: 16 pages, 2 figures, typos corrected, Refs adde
Goldstone Fermion Dark Matter
We propose that the fermionic superpartner of a weak-scale Goldstone boson
can be a natural WIMP candidate. The p-wave annihilation of this `Goldstone
fermion' into pairs of Goldstone bosons automatically generates the correct
relic abundance, whereas the XENON100 direct detection bounds are evaded due to
suppressed couplings to the Standard Model. Further, it is able to avoid
indirect detection constraints because the relevant s-wave annihilations are
small. The interactions of the Goldstone supermultiplet can induce non-standard
Higgs decays and novel collider phenomenology.Comment: 25 pages, 6 figures. References added, minor typos corrected.
Submitted to JHE
Deep multi-telescope photometry of NGC 5466. I. Blue Stragglers and binary systems
We present a detailed investigation of the radial distribution of blue
straggler star and binary populations in the Galactic globular cluster NGC
5466, over the entire extension of the system. We used a combination of data
acquired with the ACS on board the Hubble Space Telescope, the LBC-blue mounted
on the Large Binocular Telescope, and MEGACAM on the Canadian-France-Hawaii
Telescope. Blue straggler stars show a bimodal distribution with a mild central
peak and a quite internal minimum. This feature is interpreted in terms of a
relatively young dynamical age in the framework of the "dynamical clock"
concept proposed by Ferraro et al. (2012). The estimated fraction of binaries
is 6-7% in the central region (r<90") and slightly lower (5.5%) in the
outskirts, at r>200". Quite interestingly, the comparison with the results of
Milone et al. (2012) suggests that also binary systems may display a bimodal
radial distribution, with the position of the minimum consistent with that of
blue straggler stars. If confirmed, this feature would give additional support
to the scenario where the radial distribution of objects more massive than the
average cluster stars is primarily shaped by the effect of dynamical friction.
Moreover, this would also be consistent with the idea that the unperturbed
evolution of primordial binaries could be the dominant BSS formation process in
low-density environments.Comment: Accepted for publication on Ap
The fine-tuning price of the early LHC
LHC already probed and excluded half of the parameter space of the
Constrained Minimal Supersymmetric Standard Model allowed by previous
experiments. Only about 0.3% of the CMSSM parameter space survives. This
fraction rises to about 0.9% if the bound on the Higgs mass can be
circumvented.Comment: 7 pages. v3: updated with new bounds from ATLAS and CMS at 1.1/fb
presented at the EPS-HEP-2011 conferenc
Goldstones in Diphotons
We study the conditions for a new scalar resonance to be observed first in
diphotons at the LHC Run-2. We focus on scenarios where the scalar arises
either from an internal or spacetime symmetry broken spontaneously, for which
the mass is naturally below the cutoff and the low-energy interactions are
fixed by the couplings to the broken currents, UV anomalies, and selection
rules. We discuss the recent excess in diphoton resonance searches observed by
ATLAS and CMS at 750 GeV, and explore its compatibility with other searches at
Run-1 and its interpretation as Goldstone bosons in supersymmetry and composite
Higgs models. We show that two candidates naturally emerge: a Goldstone boson
from an internal symmetry with electromagnetic anomalies, and the scalar
partner of the Goldstone of supersymmetry breaking: the sgoldstino. The dilaton
from conformal symmetry breaking is instead disfavoured by present data, in its
minimal natural realization.Comment: 18 pages + refs, 2 figures. v2: typos corrected, references added,
discussions extended and three new plots. Conclusion unchanged. v3: published
versio
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