17 research outputs found
Relative locality: A deepening of the relativity principle
We describe a recently introduced principle of relative locality which we
propose governs a regime of quantum gravitational phenomena accessible to
experimental investigation. This regime comprises phenomena in which
and may be neglected, while their ratio, the Planck mass , is important. We propose that governs the scale at
which momentum space may have a curved geometry. We find that there are
striking consequences for the concept of locality. The description of events in
spacetime now depends on the energy used to probe it. But there remains an
invariant description of physics in phase space. There is furthermore a
reasonable expectation that the geometry of momentum space can be measured
experimentally using astrophysical observations.Comment: 8 pages, Latex; this essay was awarded Second Prize in the 2011 Essay
Competition of the Gravity Research Foundatio
Valence band excitations in V_2O_5
We present a joint theoretical and experimental investigation of the
electronic and optical properties of vanadium pentoxide. Electron energy-loss
spectroscopy in transmission was employed to measure the momentum-dependent
loss function. This in turn was used to derive the optical conductivity, which
is compared to the results of band structure calculations. A good qualitative
and quantitative agreement between the theoretical and the experimental optical
conductivity was observed. The experimentally observed anisotropy of the
optical properties of V_2O_5 could be understood in the light of an analysis of
the theoretical data involving the decomposition of the calculated optical
conductivity into contributions from transitions into selected energy regions
of the conduction band. In addition, based upon a tight binding fit to the band
structure, values are given for the effective V3d_xy-O2p hopping terms and are
compared to the corresponding values for alpha'-NaV_2O_5.Comment: 6 pages (revtex),6 figures (jpg
Constraints on the Ultra High Energy Photon flux using inclined showers from the Haverah Park array
We describe a method to analyse inclined air showers produced by ultra high
energy cosmic rays using an analytical description of the muon densities. We
report the results obtained using data from inclined events
(60^{\circ}<\theta<80^{\circ}) recorded by the Haverah Park shower detector for
energies above 10^19 eV. Using mass independent knowledge of the UHECR spectrum
obtained from vertical air shower measurements and comparing the expected
horizontal shower rate to the reported measurements we show that above 10^19 eV
less than 48 % of the primary cosmic rays can be photons at the 95 % confidence
level and above 4 X 10^19 eV less than 50 % of the cosmic rays can be photonic
at the same confidence level. These limits place important constraints on some
models of the origin of ultra high-energy cosmic rays.Comment: 45 pages, 25 figure
Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei
In this article we examine the hypothesis that the highest energy cosmic rays
are complex nuclei from extragalactic sources. Under reasonable physical
assumptions, we show that the nearby metally rich starburst galaxies (M82 and
NGC 253) can produce all the events observed above the ankle. This requires
diffusion of particles below eV in extragalactic magnetic fields nG. Above eV, the model predicts the presence of
significant fluxes of medium mass and heavy nuclei with small rate of change of
composition. Notwithstanding, the most salient feature of the
starburst-hypothesis is a slight anisotropy induced by iron debris just before
the spectrum-cutoff.Comment: To appear in Phys. Rev. D, reference adde
Anisotropy at the end of the cosmic ray spectrum?
The starburst galaxies M82 and NGC253 have been proposed as the primary
sources of cosmic rays with energies above eV. For energies \agt
10^{20.3} eV the model predicts strong anisotropies. We calculate the
probabilities that the latter can be due to chance occurrence. For the highest
energy cosmic ray events in this energy region, we find that the observed
directionality has less than 1% probability of occurring due to random
fluctuations. Moreover, during the first 5 years of operation at Auger, the
observation of even half the predicted anisotropy has a probability of less
than to occur by chance fluctuation. Thus, this model can be subject
to test at very small cost to the Auger priors budget and, whatever the outcome
of that test, valuable information on the Galactic magnetic field will be
obtained.Comment: Final version to be published in Physical Review
A search for resonances decaying into a Higgs boson and a new particle X in the XH â qqbb final state with the ATLAS detector
A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fbâ1 of protonâproton collision data at collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle X is assumed to decay to a pair of light quarks, and the fully hadronic final state is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the resonance