106 research outputs found
How wearing headgear affects measured head-related transfer functions
International audienceThe spatial representation of sound sources is an essential element of virtual acoustic environments (VAEs). When determining the sound incidence direction, the human auditory system evaluates monaural and binaural cues, which are caused by the shape of the pinna and the head. While spectral information is the most important cue for elevation of a sound source, we use differences between the signals reaching the left and the right ear for lateral localization. These binaural differences manifest in interaural time differences (ITDs) and interaural level differences (ILDs). In many headphone-based VAEs, head-related transfer functions (HRTFs) are used to describe the sound incidence from a source to the left and right ear, thus integrating both monaural and the binaural cues. Specific aspects, like for example the individual shape of the head and the outer ears (e.g. Bomhardt, 2017), of the torso (Brinkmann et al., 2015), and probably even of headgear (Wersenyi, 2005; Wersenyi, 2017) influence the HRTFs and thus probably as well localization and other perceptual attributes.<par>Generally speaking, spatial cues are modified by headgear, for example by wearing a baseball cap, a bicycle helmet, or a head-mounted display, which nowadays is often used in VR applications. In many real life situations, however, a good localization performance is important when wearing such items, e.g. in order to determine approaching vehicles when cycling. Furthermore, when performing psychoacoustic experiments in mixed-reality applications using head-mounted displays, the influence of the head-mounted display on the HRTFs must be considered. Effects of an HTC Vive head-mounted display on localization performance have already been shown in Ahrens et al. (2018). To analyze the influence of headgear for varying directions of incidence, measurements of HRTFs on a dense spherical sampling grid are required. However, HRTF measurements of a dummy head with various headgear are still rare, and to our knowledge only one dataset measured for an HTC Vice on a sparse grid with 64 positions is freely accessible (Ahrens, 2018).<par>This work presents high-density measurement data of HRTFs from a Neumann KU100 and a HEAD acoustics HMS II.3 dummy head, either equipped with a bicycle helmet, a baseball cap, an Oculus Rift head-mounted display, or a set of extra-aural AKG K1000 headphones. For the measurements, we used the VariSphear measurement system (BernschĂĽtz, 2010), allowing precise positioning of the dummy head at the spatial sampling positions. The various HRTF sets were captured on a full spherical Lebedev grid with 2702 points.<par>In our study, we analyze the measured datasets in terms of their spectrum, their binaural cues, and regarding their localization performance based on localization models, and compare the results to reference measurements of the dummy heads without headgear. The results show that differences to the reference without headgear vary significantly depending on the type of the headgear. Regarding the ITDs and ILDs, the analysis reveals the highest influences for the AKG K1000. While for the Oculus Rift head-mounted display, the ITDs and ILDs are mainly affected for frontal directions, only a very weak influence of the bicycle helmet and the baseball cap on ITDs and ILDs was observed. For the spectral differences to the reference the results show maximal deviations for the AKG K1000, the lowest for the Oculus Rift and the baseball cap. Furthermore, we analyzed for which incidence directions the spectrum is influenced most by the headgears. For the Oculus Rift and the baseball cap, the strongest deviations were found for contralateral sound incidence. For the bicycle helmet, the directions mostly affected are as well contralateral, but shifted upwards in elevation. Finally, the AKG K1000 headphones generally has the highest influence on the measured HRTFs, which becomes maximal for sound incidence from behind.<par>The results of this study are relevant for applications where headgears are worn and localization or other aspects of spatial hearing are considered. This could be the case, for example in mixed-reality applications where natural sound sources are presented while the listener is wearing a head-mounted display, or when investigating localization performance in certain situations, e.g. in sports activities where headgears are used. However, it is an important intention of this study to provide a freely available database of HRTF sets which is well suited for auralization purposes and which allows to further investigate the influence of headgear on auditory perception. The HRTF sets will be publicly available in the SOFA format under a Creative Commons CC BY-SA 4.0 license
Dangerous Skyrmions in Little Higgs Models
Skyrmions are present in many models of electroweak symmetry breaking where
the Higgs is a pseudo-Goldstone boson of some strongly interacting sector. They
are stable, composite objects whose mass lies in the range 10-100 TeV and can
be naturally abundant in the universe due to their small annihilation
cross-section. They represent therefore good dark matter candidates. We show
however in this work that the lightest skyrmion states are electrically charged
in most of the popular little Higgs models, and hence should have been directly
or indirectly observed in nature already. The charge of the skyrmion under the
electroweak gauge group is computed in a model-independent way and is related
to the presence of anomalies in the underlying theory via the
Wess-Zumino-Witten term.Comment: 31 pages, 4 figures; v2: minor changes, one reference added, version
to appear in JHEP; v3: erratum added, conclusions unchange
Classical skyrmions in SU(N)/SO(N) cosets
We construct the skyrmion solutions appearing in the coset spaces SU(N)/SO(N)
for N > 2 and compute their classical mass. For N = 3, the third homotopy group
pi_3(SU(3)/SO(3)) = Z_4 implies the existence of two distinct solutions: the
skyrmion of winding number two has spherical symmetry and is found to be the
lightest non-trivial field configuration; the skyrmion and antiskyrmion of
winding number plus and minus one are slightly heavier and of toroidal shape.
For N >= 4, there is only one skyrmion since the third homotopy group is Z_2.
It is found to have spherical symmetry and is significantly lighter than the N
= 3 solutions.Comment: 14 pages, 3 figures; v2: discussion improve
Partially Supersymmetric Composite Higgs Models
We study the idea of the Higgs as a pseudo-Goldstone boson within the
framework of partial supersymmetry in Randall-Sundrum scenarios and their CFT
duals. The Higgs and third generation of the MSSM are composites arising from a
strongly coupled supersymmetric CFT with global symmetry SO(5) spontaneously
broken to SO(4), whilst the light generations and gauge fields are elementary
degrees of freedom whose couplings to the strong sector explicitly break the
global symmetry as well as supersymmetry. The presence of supersymmetry in the
strong sector may allow the compositeness scale to be raised to ~10 TeV without
fine tuning, consistent with the bounds from precision electro-weak
measurements and flavour physics. The supersymmetric flavour problem is also
solved. At low energies, this scenario reduces to the "More Minimal
Supersymmetric Standard Model" where only stops, Higgsinos and gauginos are
light and within reach of the LHC.Comment: 28 pages. v2 minor changes and Refs. adde
Phenomenology and Cosmology of an Electroweak Pseudo-Dilaton and Electroweak Baryons
In many strongly-interacting models of electroweak symmetry breaking the
lowest-lying observable particle is a pseudo-Goldstone boson of approximate
scale symmetry, the pseudo-dilaton. Its interactions with Standard Model
particles can be described using a low-energy effective nonlinear chiral
Lagrangian supplemented by terms that restore approximate scale symmetry,
yielding couplings of the pseudo-dilaton that differ from those of a Standard
Model Higgs boson by fixed factors. We review the experimental constraints on
such a pseudo-dilaton in light of new data from the LHC and elsewhere. The
effective nonlinear chiral Lagrangian has Skyrmion solutions that may be
identified with the `electroweak baryons' of the underlying
strongly-interacting theory, whose nature may be revealed by the properties of
the Skyrmions. We discuss the finite-temperature electroweak phase transition
in the low-energy effective theory, finding that the possibility of a
first-order electroweak phase transition is resurrected. We discuss the
evolution of the Universe during this transition and derive an
order-of-magnitude lower limit on the abundance of electroweak baryons in the
absence of a cosmological asymmetry, which suggests that such an asymmetry
would be necessary if the electroweak baryons are to provide the cosmological
density of dark matter. We revisit estimates of the corresponding
spin-independent dark matter scattering cross section, with a view to direct
detection experiments.Comment: 34 pages, 4 figures, additional references adde
Discovery potential of top-partners in a realistic composite Higgs model with early LHC data
Composite Higgs models provide a natural, non-supersymmetric solution to the
hierarchy problem. In these models, one or more sets of heavy top-partners are
typically introduced. Some of these new quarks can be relatively light, with a
mass of a few hundred GeV, and could be observed with the early LHC collision
data expected to be collected during 2010. We analyse in detail the collider
signatures that these new quarks can produce. We show that final states with
two (same-sign) or three leptons are the most promising discovery channels.
They can yield a 5 sigma excess over the Standard Model expectation already
with the 2010 LHC collision data. Exotic quarks of charge 5/3 are a distinctive
feature of this model. We present a new method to reconstruct their masses from
their leptonic decay without relying on jets in the final state.Comment: 28 pages 11 Figures 7 Tables, minor changes, added references,
matches published versio
Higgs Low-Energy Theorem (and its corrections) in Composite Models
The Higgs low-energy theorem gives a simple and elegant way to estimate the
couplings of the Higgs boson to massless gluons and photons induced by loops of
heavy particles. We extend this theorem to take into account possible nonlinear
Higgs interactions resulting from a strong dynamics at the origin of the
breaking of the electroweak symmetry. We show that, while it approximates with
an accuracy of order a few percents single Higgs production, it receives
corrections of order 50% for double Higgs production. A full one-loop
computation of the gg->hh cross section is explicitly performed in MCHM5, the
minimal composite Higgs model based on the SO(5)/SO(4) coset with the Standard
Model fermions embedded into the fundamental representation of SO(5). In
particular we take into account the contributions of all fermionic resonances,
which give sizeable (negative) corrections to the result obtained considering
only the Higgs nonlinearities. Constraints from electroweak precision and
flavor data on the top partners are analyzed in detail, as well as direct
searches at the LHC for these new fermions called to play a crucial role in the
electroweak symmetry breaking dynamics.Comment: 30 pages + appendices and references, 12 figures. v2: discussion of
flavor constraints improved; references added; electroweak fit updated,
results unchanged. Matches published versio
Composite Higgs Sketch
The coupling of a composite Higgs to the standard model fields can deviate
substantially from the standard model values. In this case perturbative
unitarity might break down before the scale of compositeness is reached, which
would suggest that additional composites should lie well below this scale. In
this paper we account for the presence of an additional spin 1 custodial
triplet of rhos. We examine the implications of requiring perturbative
unitarity up to the compositeness scale and find that one has to be close to
saturating certain unitarity sum rules involving the Higgs and the rho
couplings. Given these restrictions on the parameter space we investigate the
main phenomenological consequences of the spin 1 triplet. We find that they can
substantially enhance the Higgs di-photon rate at the LHC even with a reduced
Higgs coupling to gauge bosons. The main existing LHC bounds arise from
di-boson searches, especially in the experimentally clean channel where the
charged rhos decay to a W-boson and a Z, which then decay leptonically. We find
that a large range of interesting parameter space with 700 GeV < m(rho) < 2 TeV
is currently experimentally viable.Comment: 37 pages, 12 figures; v4: sum rule corrected, conclusions unchange
Exploring T and S parameters in Vector Meson Dominance Models of Strong Electroweak Symmetry Breaking
We revisit the electroweak precision tests for Higgsless models of strong
EWSB. We use the Vector Meson Dominance approach and express S and T via
couplings characterizing vector and axial spin-1 resonances of the strong
sector. These couplings are constrained by the elastic unitarity and by
requiring a good UV behavior of various formfactors. We pay particular
attention to the one-loop contribution of resonances to T (beyond the chiral
log), and to how it can improve the fit. We also make contact with the recent
studies of Conformal Technicolor. We explain why the second Weinberg sum rule
never converges in these models, and formulate a condition necessary for
preserving the custodial symmetry in the IR.Comment: 35 pages, 7 figures; v3: refs added, to appear in JHE
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