3,205 research outputs found

### Search for Extra Space-Dimensions at the LHC

The introduction of extra space dimensions in the theory could be an elegant
way tovsolve the hierarchy problem. There could even be one energy scale at
which all interactions could unify. The limits coming from our knowledge of the
gravitation at low distance allow this energy scale to be as low as few TeV.
This situation is extremely interesting experimentally in the context of the
LHC which will cover the range from 100 GeV to few TeV. This article describes
the different analyses developed by the LHC experiments to study this new
phenomenology.Comment: 7 pages, 6 figure

### Optical characterization of Bi$_2$Se$_3$ in a magnetic field: infrared evidence for magnetoelectric coupling in a topological insulator material

We present an infrared magneto-optical study of the highly thermoelectric
narrow-gap semiconductor Bi$_2$Se$_3$. Far-infrared and mid-infrared (IR)
reflectance and transmission measurements have been performed in magnetic
fields oriented both parallel and perpendicular to the trigonal $c$ axis of
this layered material, and supplemented with UV-visible ellipsometry to obtain
the optical conductivity $\sigma_1(\omega)$. With lowering of temperature we
observe narrowing of the Drude conductivity due to reduced quasiparticle
scattering, as well as the increase in the absorption edge due to direct
electronic transitions. Magnetic fields $H \parallel c$ dramatically
renormalize and asymmetrically broaden the strongest far-IR optical phonon,
indicating interaction of the phonon with the continuum free-carrier spectrum
and significant magnetoelectric coupling. For the perpendicular field
orientation, electronic absorption is enhanced, and the plasma edge is slightly
shifted to higher energies. In both cases the direct transition energy is
softened in magnetic field.Comment: Final versio

### Ion-lithium collision dynamics studied with an in-ring MOTReMi

We present a novel experimental tool allowing for kinematically complete
studies of break-up processes of laser-cooled atoms. This apparatus, the
'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction
Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to
study the dynamics in swift ion-atom collisions on an unprecedented level of
precision and detail. In first experiments on collisions with 1.5 MeV/amu
O$^{8+}$-Li the pure ionization of the valence electron as well as
ionization-excitation of the lithium target has been investigated

### Probing TeV-scale gauge unification by hadronic collisions

Grand unified theories (GUTs) and extra dimensions are potential ingredients
of the new physics that may resolve various outstanding problems of the
Standard Model. If the inverse size of (one of) the extra dimension(s) is
smaller than the GUT scale and standard gauge bosons are allowed to propagate
in the bulk then, among other consequences, the evolution of the gauge
couplings deviates from the usual logarithmic running somewhat below and
between these two scales.
In this work, we show that if the compactification scale is the order of 10
TeV, then this modified running may be observable at the CERN Large Hadron
Collider in the dijet invariant mass distribution. We also demonstrate that
dijets are highly sensitive to the renormalization effects of the extra
dimensions, and are potential tools for determining the number of dimensions
and the value of the compactification scale.Comment: 10 pages, 2 figures, using JHEP styl

### Forecasting the quality of AMF communities

Non-Peer Reviewe

### Phonon splitting and anomalous enhancement of infrared-active modes in BaFe$_2$As$_2$

We present a comprehensive infrared spectroscopic study of lattice dynamics
in the pnictide parent compound BaFe$_2$As$_2$. In the tetragonal structural
phase, we observe the two degenerate symmetry-allowed in-plane infrared active
phonon modes. Following the structural transition from the tetragonal to
orthorhombic phase, we observe splitting into four non-degenerate phonon modes
and a significant phonon strength enhancement. These detailed data allow us to
provide a physical explanation for the anomalous phonon strength enhancement as
the result of anisotropic conductivity due to Hund's coupling.Comment: 5 pages, 3 figures, 1 tabl

### Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy.

A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge

### Two-Stage Rotational Disordering of a Molecular Crystal Surface: C60

We propose a two-stage mechanism for the rotational surface disordering phase
transition of a molecular crystal, as realized in C$_{60}$ fullerite. Our
study, based on Monte Carlo simulations, uncovers the existence of a new
intermediate regime, between a low temperature ordered $(2 \times 2)$ state,
and a high temperature $(1 \times 1)$ disordered phase. In the intermediate
regime there is partial disorder, strongest for a subset of particularly
frustrated surface molecules. These concepts and calculations provide a
coherent understanding of experimental observations, with possible extension to
other molecular crystal surfaces.Comment: 4 pages, 2 figure

### Polarization and Interference Effects in Ionization of Li by Ion Impact

We present initial-state selective fully differential cross sections for ionization of lithium by 24 MeV O8+ impact. The data for ionization from the 2s and 2p states look qualitatively different from each other and from 1s ionization of He. For ionization from the 2p state, to which in our study the mL=-1 substate predominantly contributes, we observe orientational dichroism and for 2s ionization pronounced interference which we trace back to the nodal structure of the initial-state wave function

### Matter-gravity interaction in a multiply warped braneworld,

The role of a bulk graviton in predicting the signature of extra dimensions
through collider-based experiments is explored in the context of a multiply
warped spacetime. In particular it is shown that in a doubly warped braneworld
model, the presence of the sixth dimension, results in enhanced concentration
of graviton Kaluza Klein (KK) modes compared to that obtained in the usual
5-dimensional Randall-Sundrum model. Also, the couplings of these massive
graviton KK modes with the matter fields on the visible brane turn out to be
appreciably larger than that in the corresponding 5- dimensional model. The
significance of these results are discussed in the context of KK graviton
search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table

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