157 research outputs found
Displaced vertices and long-lived charged particles in the NMSSM with right-handed sneutrinos
We study LHC signatures of displaced vertices and long-lived charged particles within the context of the Next-to-Minimal Supersymmetric Standard Model with right-handed (RH) sneutrinos. In this construction the RH neutrino can be produced directly from Higgs decays or in association with a RH sneutrino when the latter is the lightest supersymmetric particle. The RH neutrino is generally long-lived, since its decay width is proportional to the neutrino Yukawa, a parameter which is predicted to be small. The RH neutrino late decay can therefore give rise to displaced vertices at the LHC, which can be identified through the decay products, which involve two leptons (2ℓ + https://static-content.springer.com/image/art%3A10.1007%2FJHEP05%282014%29035/MediaObjects/13130_2014_8145_Figa_HTML.gifT ) or a lepton with two jets (ℓjj). We simulate this signal for the current LHC configuration (a centre of mass of 8 TeV and an integrated luminosity of LL = 20 fb−1), and a future one (13 TeV and LL = 100 fb−1). We show that a region of the parameter space of this model can be probed and that the RH neutrino mass can be reconstructed from the end-point of the two-lepton invariant mass distribution or the central value of the mass distribution for two jets plus one lepton. Another exotic signature of this construction is the production of a long-lived stau. If the stau is the next-to-lightest supersymmetric particle, it can decay through diagrams involving the small neutrino Yukawa, and would escape the detector leaving a characteristic trail. We also simulate this signal for various benchmark points and show that the model can be within the reach of the future run of the LHC
Experimental and theoretical investigations on a CVD grown thin film of polymeric carbon nitride and its structure
A polymeric carbon nitride thin film has been grown using chemical vapor deposition. The characterization of the material shows that it has the same molecular composition as a formerly synthesized graphitic carbon nitride powder but both substances differ widely in their structural organization. In particular, our analyses reveal a paradoxical character in which the thin film sample exhibits simultaneously a high degree of organization in the stacking of the polymer sheets with strong inter-layer interactions, as expected from the growth technique, and a complete lack of crystallinity. A comprehensive theoretical study based on massive semi-empirical quantum chemistry computations has permitted to explain the properties of the material and to elucidate fundamental issues regarding the structural conformation of graphitic carbon nitride
Non-perturbative effective field theory for two-leg antiferromagnetic spin ladders
We study the long wavelength limit of a spin 1/2 Heisenberg antiferromagnetic
two-leg ladder, treating the interchain coupling in a non-perturbative way. We
perform a mean field analysis and then include exactly the fluctuations. This
allows for a discussion of the phase diagram of the system and provides an
effective field theory for the low energy excitations. The coset fermionic
Lagrangian obtained corresponds to a perturbed SU(4)_1/U(1) Conformal Field
Theory (CFT). This effective theory is naturally embedded in a SU(2)_2 x Z_2
CFT, where perturbations are easily identified in terms of conformal operators
in the two sectors. Crossed and zig-zag ladders are also discussed using the
same approach.Comment: 14 pages LaTeX, 5 PostScript figures included using epsfig.sty; minor
corrections and a few references adde
Linear Response, Validity of Semi-Classical Gravity, and the Stability of Flat Space
A quantitative test for the validity of the semi-classical approximation in
gravity is given. The criterion proposed is that solutions to the
semi-classical Einstein equations should be stable to linearized perturbations,
in the sense that no gauge invariant perturbation should become unbounded in
time. A self-consistent linear response analysis of these perturbations, based
upon an invariant effective action principle, necessarily involves metric
fluctuations about the mean semi-classical geometry, and brings in the
two-point correlation function of the quantum energy-momentum tensor in a
natural way. This linear response equation contains no state dependent
divergences and requires no new renormalization counterterms beyond those
required in the leading order semi-classical approximation. The general linear
response criterion is applied to the specific example of a scalar field with
arbitrary mass and curvature coupling in the vacuum state of Minkowski
spacetime. The spectral representation of the vacuum polarization function is
computed in n dimensional Minkowski spacetime, and used to show that the flat
space solution to the semi-classical Einstein equations for n=4 is stable to
all perturbations on distance scales much larger than the Planck length.Comment: 22 pages: This is a significantly expanded version of gr-qc/0204083,
with two additional sections and two new appendices giving a complete,
explicit example of the semi-classical stability criterion proposed in the
previous pape
A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field
We present experimental results for the ground state electrochemical
potentials of a few electron semiconductor artificial molecule made by
vertically coupling two quantum dots, in the intermediate coupling regime, in
perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative
analysis based on local-spin density functional theory. The agreement between
theoretical and experimental results is good, and the phase transitions are
well reproduced.Comment: Typeset using Revtex, 13 pages and 8 Postscript figure
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