833 research outputs found
Dark Matter and Neutrino Mass from the Smallest Non-Abelian Chiral Dark Sector
All pieces of concrete evidence for phenomena outside the standard model (SM)
- neutrino masses and dark matter - are consistent with the existence of new
degrees of freedom that interact very weakly, if at all, with those in the SM.
We propose that these new degrees of freedom organize themselves into a simple
dark sector, a chiral SU(3) x SU(2) gauge theory with the smallest nontrivial
fermion content. Similar to the SM, the dark SU(2) is spontaneously broken
while the dark SU(3) confines at low energies. At the renormalizable level, the
dark sector contains massless fermions - dark leptons - and stable massive
particles - dark protons. We find that dark protons with masses between 10-100
TeV satisfy all current cosmological and astrophysical observations concerning
dark matter even if dark protons are a symmetric thermal relic. The dark
leptons play the role of right-handed neutrinos and allow simple realizations
of the seesaw mechanism or the possibility that neutrinos are Dirac fermions.
In the latter case, neutrino masses are also parametrically different from
charged-fermion masses and the lightest neutrino is predicted to be massless.
Since the new "neutrino" and "dark matter" degrees of freedom interact with one
another, these two new-physics phenomena are intertwined. Dark leptons play a
nontrivial role in early universe cosmology while indirect searches for dark
matter involve, decisively, dark matter annihilations into dark leptons. These,
in turn, may lead to observable signatures at high-energy neutrino and
gamma-ray observatories, especially once one accounts for the potential
Sommerfeld enhancement of the annihilation cross-section, derived from the
low-energy dark-sector effective theory, a possibility we explore
quantitatively in some detail.Comment: 35 pages, 7 figures. Matches published versio
Non-Unitary Neutrino Propagation From Neutrino Decay
Neutrino propagation in space-time is not constrained to be unitary if very
light states - lighter than the active neutrinos - exist into which neutrinos
may decay. If this is the case, neutrino flavor-change is governed by a handful
of extra mixing and "oscillation" parameters, including new sources of
CP-invariance violation. We compute the transition probabilities in the two-
and three-flavor scenarios and discuss the different phenomenological
consequences of the new physics. These are qualitatively different from other
sources of unitarity violation discussed in the literature.Comment: 8 pages, no figure
Lepton-Number-Charged Scalars and Neutrino Beamstrahlung
Experimentally, baryon number minus lepton number, , appears to be a
good global symmetry of nature. We explore the consequences of the existence of
gauge-singlet scalar fields charged under -- dubbed lepton-number-charged
scalars, LeNCS -- and postulate that these couple to the standard model degrees
of freedom in such a way that is conserved even at the non-renormalizable
level. In this framework, neutrinos are Dirac fermions. Including only the
lowest mass-dimension effective operators, some of the LeNCS couple
predominantly to neutrinos and may be produced in terrestrial neutrino
experiments. We examine several existing constraints from particle physics,
astrophysics, and cosmology to the existence of a LeNCS carrying charge
equal to two, and discuss the emission of LeNCS's via "neutrino beamstrahlung,"
which occurs every once in a while when neutrinos scatter off of ordinary
matter. We identify regions of the parameter space where existing and future
neutrino experiments, including the Deep Underground Neutrino Experiment, are
at the frontier of searches for such new phenomena.Comment: 18 pages, 7 figures, 1 Appendi
Seeing the body distorts tactile size perception
Vision of the body modulates somatosensation, even when entirely non-informative about stimulation. For example, seeing the body increases tactile spatial acuity, but reduces acute pain. While previous results demonstrate that vision of the body modulates somatosensory sensitivity, it is unknown whether vision also affects metric properties of touch, and if so how. This study investigated how non-informative vision of the body modulates tactile size perception. We used the mirror box illusion to induce the illusion that participants were directly seeing their stimulated left hand, though they actually saw their reflected right hand. We manipulated whether participants: (a) had the illusion of directly seeing their stimulated left hand, (b) had the illusion of seeing a non-body object at the same location, or (c) looked directly at their non-stimulated right-hand. Participants made verbal estimates of the perceived distance between two tactile stimuli presented simultaneously to the dorsum of the left hand, either 20, 30, or 40 mm apart. Vision of the body significantly reduced the perceived size of touch, compared to vision of the object or of the contralateral hand. In contrast, no apparent changes of perceived hand size were found. These results show that seeing the body distorts tactile size perception
Scaling in Small-World Resistor Networks
We study the effective resistance of small-world resistor networks. Utilizing
recent analytic results for the propagator of the Edwards-Wilkinson process on
small-world networks, we obtain the asymptotic behavior of the
disorder-averaged two-point resistance in the large system-size limit. We find
that the small-world structure suppresses large network resistances: both the
average resistance and its standard deviation approaches a finite value in the
large system-size limit for any non-zero density of random links. We also
consider a scenario where the link conductance decays as a power of the length
of the random links, . In this case we find that the average
effective system resistance diverges for any non-zero value of .Comment: 15 pages, 6 figure
Pest categorisation of Dendroctonus micans
The Panel on Plant Health performed a pest categorisation of the great spruce bark beetle,
Dendroctonus micans (Kugelann), (Coleoptera: Curculionidae, Scolytinae), for the EU. D. micans is a
well-defined and distinguishable species, recognised mainly as a pest of spruce (Picea spp.) and pine
(Pinus spp.) in Eurasia. Attacks on other conifers (Abies spp., Larix decidua, Pseudotsuga menziesii)
are also reported. Supposedly originating from north-eastern Eurasia, D. micans has spread westward
and is now distributed throughout the EU (22 Member States). It is a quarantine pest listed in Annex
IIB of Council Directive 2000/29/EC for Greece, Ireland and the United Kingdom (Northern Ireland, Isle
of Man and Jersey) as protected zones. Wood, wood products, bark and wood packaging material of
the conifers genera listed as hosts are considered as the main pathways for the pest, which is also
able to disperse several kilometres by flight. The sib-mating habits of the species allow each single
female to start a new colony on her own. The pestâs wide current geographic range suggests that it is
able to establish anywhere in the EU where its hosts are present. The beetles attack living trees and
usually complete their life cycle without killing their host, except under epidemic conditions at the
limits of their distribution range, where hundreds of thousands of trees can be killed. Sitka spruce
(Picea sitchensis) is particularly susceptible. Biological control using the very specific predatory beetle,
Rhizophagus grandis, is a widespread and efficient option that has been implemented in all areas
suffering from outbreaks. It is complemented by sanitary thinning or clear-felling. All criteria assessed
by EFSA for consideration as potential protected zone quarantine pest were met. The criteria for
considering D. micans as a potential regulated non-quarantine pest are not met since plants for
planting are not the main pathway
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