2,916 research outputs found

### Characterizing Boosted Dijet Resonances with Jet Energy Correlators

We show that Jet Energy Correlation variables can be used effectively to
discover and distinguish a wide variety of boosted light dijet resonances at
the LHC through sensitivity to their transverse momentum and color structures.Comment: 8 pages, 4 figure

### Field-induced length changes in the spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$

Measurements of the coefficient of thermal expansion on the spin-liquid
candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ have revealed distinct and
strongly anisotropic lattice effects around 6 K - a possible spin-liquid
instability. In order to study the effects of a magnetic field on the
low-temperature spin-liquid state, dilatometric measurements have been
conducted both as a function of temperature at \emph{B} = const. and as a
function of field at \emph{T} = const. While the 6 K anomaly is found to be
insensitive to magnetic fields \emph{B} $\leq$ 10 T, the maximum field applied,
surprisingly strong \emph{B}-induced effects are observed for magnetic fields
applied along the in-plane \emph{b}-axis. Above a threshold field of 0.5 T <
\emph{B}$_c$ $\leq$ 1 T, a jump-like anomaly is observed in the \emph{b}-axis
lattice parameter. This anomaly, which is located at 8.7 K at \emph{B} = 1 T,
grows in size and shifts to lower temperatures with increasing the magnetic
field. Although the anomaly bears resemblance to a first-order phase
transition, the lack of hysteresis suggests otherwise.Comment: 3 pages, 3 figures, proceedings of ISCOM 2011, physica status solidi
(c)(in press

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### Scattering amplitudes of massive spin-2 Kaluza-Klein states grow only as O(s)

We present the results of the first complete calculation of the tree-level
$2\to 2$ high-energy scattering amplitudes of the longitudinal modes of massive
spin-2 Kaluza-Klein states, both in the case where the internal space is a
torus and in the Randall-Sundrum model where the internal space has constant
negative curvature. While individual contributions to this amplitude grow as
${\cal O}(s^5$), we demonstrate explicitly that intricate cancellations occur
between different contributions, reducing the growth to ${\cal O}(s)$, a slower
rate of growth than previously argued in the literature. These cancellations
require subtle relationships between the masses of the Kaluza-Klein states and
their interactions, and reflect the underlying higher-dimensional
diffeomorphism invariance. Our results provide fresh perspective on the range
of validity of (effective) field theories involving massive spin-2 KK
particles, with significant implications for the theory and phenomenology of
these states

### Massive spin-2 scattering amplitudes in extra-dimensional theories

In this paper we describe in detail the computation of the scattering
amplitudes of massive spin-2 Kaluza-Klein excitations in a gravitational theory
with a single compact extra dimension, whether flat or warped. These scattering
amplitudes are characterized by intricate cancellations between different
contributions: although individual contributions may grow as fast as ${\cal
O}(s^5)$, the full results grow only as ${\cal O}(s)$. We demonstrate that the
cancellations persist for all incoming and outgoing particle helicities and
examine how truncating the computation to only include a finite number of
intermediate states impacts the accuracy of the results. We also carefully
assess the range of validity of the low energy effective Kaluza-Klein theory.
In particular, for the warped case we demonstrate directly how an emergent low
energy scale controls the size of the scattering amplitude, as conjectured by
the AdS/CFT correspondence

### Sum rules for massive spin-2 Kaluza-Klein elastic scattering amplitudes

It has recently been shown explicitly that the high-energy scattering
amplitude of the longitudinal modes of massive spin-2 Kaluza Klein states in
compactified 5-dimensional gravity, which would naively grow like O(s^5), grow
only like O(s). Since the individual contributions to these amplitudes do grow
like O(s^5), the required cancellations between these individual contributions
result from intricate relationships between the masses of these states and
their couplings. Here we report the explicit form of these sum-rule
relationships which ensure the necessary cancellations for elastic scattering
of spin-2 Kaluza Klein states in a Randall-Sundrum model. We consider an
Anti-de-Sitter space of arbitrary curvature, including the special case of a
toroidal compactification in which the curvature vanishes. The sum rules
demonstrate that the cancellations at O(s^5) and O(s^4) are generic for a
compact extra dimension, and arise from the Sturm-Liouville structure of the
eigenmode system in the internal space. Separately, the sum rules at O(s^3) and
O(s^2) illustrate the essential role of the radion mode of the
extra-dimensional metric, which is the dynamical mode related to the size of
the internal space

### Photoemission studies of the near Fermi level spectral weight shifts in FeSe1-xTex superconductor

Our valence band photoelectron spectroscopic studies show a temperature
dependent spectral weight transfer near the Fermi level in the Fe-based
superconductor FeSe1-xTex. Using theoretical band structure calculations we
have shown that the weight transfer is due to the temperature induced changes
in the Fe(Se,Te)4 tetrahedra. These structural changes lead to shifts in the
electron occupancy from the xz/yz and x2-y2 orbitals to the 3z2-r2 orbitals
indicating a temperature induced crossover from a metallic state to an Orbital
Selective Mott (OSM) Phase. Our study presents the observation of a temperature
induced crossover to a low temperature OSM phase in the family of Fe
chalcogenides.Comment: 10 pages, 4 figure

### Low-temperature lattice effects in the spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$

The quasi-two-dimensional organic charge-transfer salt
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ is one of the prime candidates for a
quantum spin-liquid due the strong spin frustration of its anisotropic
triangular lattice in combination with its proximity to the Mott transition.
Despite intensive investigations of the material's low-temperature properties,
several important questions remain to be answered. Particularly puzzling are
the 6\,K anomaly and the enigmatic effects observed in magnetic fields. Here we
report on low-temperature measurements of lattice effects which were shown to
be particularly strongly pronounced in this material (R. S. Manna \emph{et
al.}, Phys. Rev. Lett. \textbf{104}, 016403 (2010)). A special focus of our
study lies on sample-to-sample variations of these effects and their
implications on the interpretation of experimental data. By investigating
overall nine single crystals from two different batches, we can state that
there are considerable differences in the size of the second-order phase
transition anomaly around 6\,K, varying within a factor of 3. In addition, we
find field-induced anomalies giving rise to pronounced features in the sample
length for two out of these nine crystals for temperatures $T <$ 9 K. We
tentatively assign the latter effects to $B$-induced magnetic clusters
suspected to nucleate around crystal imperfections. These $B$-induced effects
are absent for the crystals where the 6\,K anomaly is most strongly pronounced.
The large lattice effects observed at 6\,K are consistent with proposed pairing
instabilities of fermionic excitations breaking the lattice symmetry. The
strong sample-to-sample variation in the size of the phase transition anomaly
suggests that the conversion of the fermions to bosons at the instability is
only partial and to some extent influenced by not yet identified
sample-specific parameters

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