509 research outputs found
Distribution and numbers of breeding ivory gulls Pagophila eburnea in Severnaja Zemlja, Russian Arctic
The ivory gull Pagophila eburnea has a semi-circumpolar distribution with breeding sites in the High Arctic. Data about ivory gulls in the Severnaja Zemlja Archipelago (Siberia) were collected from 1991 to 1995. The numbers of breeding ivory gulls and their egg-laying period are correlated with the sea ice situation and weather during the first part of the summer. We estimate that the total potential breeding population of Severnaja Zemlja is about 2000 pairs. which makes up approximately 20% of the Russian and 14% of the world ivory gull breeding population. The percentage of the total breeding population which actually breeds varies annually. The most important breeding area of the ivory gull in Severnaja Zemlja is the Sedov Archipelago (A. Sedova) where a large colony (from 410 to about 1100 pairs in different years) was found on flat ground on Domasnij Island. Colonies from 10 to 100 breeding pairs. mostly on steep cliff faces, occur on O. Oktjabr'skoj Revoljucii and O. Bol'Sevik. The ivory gull is included in the Red Data Book of Russia. Parts of Severnaja Zemlja, with important breeding sites, have become a nature reserve
A Bound on the Superpotential
We prove a general bound on the superpotential in theories with broken
supersymmetry and broken R-symmetry, 2|W|< f_a F, where f_a and F are the
R-axion and Goldstino decay constants, respectively. The bound holds for weakly
coupled as well as strongly coupled theories, thereby providing an exact result
in theories with broken supersymmetry. We briefly discuss several possible
applications.Comment: 20 page
Holographic Phase Transition to Topological Dyons
The dynamical stability of a Julia-Zee solution in the AdS background in a
four dimensional Einstein-Yang-Mills-Higgs theory is studied. We find that the
model with a vanishing scalar field develops a non-zero value for the field at
a certain critical temperature which corresponds to a topological dyon in the
bulk and a topological phase transition at the boundary.Comment: 18 pages, 2 figures, 2 tables, sections 2 and 4 are shortened, an
error in the last part of section 5 is corrected and equations are modified.
This version to be published in JHE
Search for Axionlike and Scalar Particles with the NA64 Experiment
We carried out a model-independent search for light scalar (s) and
pseudoscalar axionlike (a) particles that couple to two photons by using the
high-energy CERN SPS H4 electron beam. The new particles, if they exist, could
be produced through the Primakoff effect in interactions of hard bremsstrahlung
photons generated by 100 GeV electrons in the NA64 active dump with virtual
photons provided by the nuclei of the dump. The a(s) would penetrate the
downstream HCAL module, serving as shielding, and would be observed either
through their decay in the rest of the HCAL detector or
as events with large missing energy if the a(s) decays downstream of the HCAL.
This method allows for the probing the a(s) parameter space, including those
from generic axion models, inaccessible to previous experiments. No evidence of
such processes has been found from the analysis of the data corresponding to
electrons on target allowing to set new limits on the
-coupling strength for a(s) masses below 55 MeV.Comment: This publication is dedicated to the memory of our colleague Danila
Tlisov. 7 pages, 5 figures, revised version accepted for publication in Phys.
Rev. Let
Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators
Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.Peer ReviewedPostprint (author's final draft
The Two Faces of Anomaly Mediation
Anomaly mediation is a ubiquitous source of supersymmetry (SUSY) breaking
which appears in almost every theory of supergravity. In this paper, we show
that anomaly mediation really consists of two physically distinct phenomena,
which we dub "gravitino mediation" and "Kahler mediation". Gravitino mediation
arises from minimally uplifting SUSY anti-de Sitter (AdS) space to Minkowski
space, generating soft masses proportional to the gravitino mass. Kahler
mediation arises when visible sector fields have linear couplings to SUSY
breaking in the Kahler potential, generating soft masses proportional to beta
function coefficients. In the literature, these two phenomena are lumped
together under the name "anomaly mediation", but here we demonstrate that they
can be physically disentangled by measuring associated couplings to the
goldstino. In particular, we use the example of gaugino soft masses to show
that gravitino mediation generates soft masses without corresponding goldstino
couplings. This result naively violates the goldstino equivalence theorem but
is in fact necessary for supercurrent conservation in AdS space. Since
gravitino mediation persists even when the visible sector is sequestered from
SUSY breaking, we can use the absence of goldstino couplings as an unambiguous
definition of sequestering.Comment: 21 pages, 1 table; v2, references added, extended discussion in
introduction and appendix; v3, JHEP versio
Comments About Hamiltonian Formulation of Non-Linear Massive Gravity with Stuckelberg Fields
We perform the Hamiltonian analysis of some form of the non-linear massive
gravity action that is formulated in the Stuckelberg formalism. Following
seminal analysis performed in arXiv:1203.5283 [hep-th] we find that this theory
possesses one primary constraint which could eliminate one additional mode in
this theory. We performed the explicit Hamiltonian analysis of two dimensional
non-linear massive gravity and we found that this is theory free from the
ghosts.Comment: 17 pages,v2:typos corrected, references added, v3. Rewritten the main
body of the paper after publication of the paper arXiv:1203.5283 [hep-th]
where the primary constraint was identified so that the conclusion is
different from the first version of the paper. It is also version that is
accepted for publication in JHEP. arXiv admin note: substantial text overlap
with arXiv:1202.5899, arXiv:1204.2957, arXiv:1109.305
Confirmation of the Secondary Constraint and Absence of Ghost in Massive Gravity and Bimetric Gravity
In massive gravity and in bimetric theories of gravity, two constraints are
needed to eliminate the two phase-space degrees of freedom of the
Boulware-Deser ghost. For recently proposed non-linear theories, a Hamiltonian
constraint has been shown to exist and an associated secondary constraint was
argued to arise as well. In this paper we explicitly demonstrate the existence
of the secondary constraint. Thus the Boulware-Deser ghost is completely absent
from these non-linear massive gravity theories and from the corresponding
bimetric theories.Comment: 15 page
Improved exclusion limit for light dark matter from e+e- annihilation in NA64
The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A′ were set by the NA64 experiment for the mass region mA′≲250 MeV, by analyzing data from the interaction of 2.84×1011 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including A′ production via secondary positron annihilation with atomic electrons, we extend these limits in the 200-300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated e+ beam efforts
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