3,541 research outputs found
Massive photons and Lorentz violation
All quadratic translation- and gauge-invariant photon operators for Lorentz
breakdown are included into the Stueckelberg Lagrangian for massive photons in
a generalized \xi-gauge. The corresponding dispersion relation and tree-level
propagator are determined exactly, and some leading-order results are derived.
The question of how to include such Lorentz-violating effects into a
perturbative quantum-field expansion is addressed. Applications of these
results within Lorentz-breaking quantum field theories include the
regularization of infrared divergences as well as the free propagation of
massive vector bosons.Comment: 12 pages, 1 figur
CPT and Lorentz-invariance violation
The largest gap in our understanding of nature at the fundamental level is
perhaps a unified description of gravity and quantum theory. Although there are
currently a variety of theoretical approaches to this question, experimental
research in this field is inhibited by the expected Planck-scale suppression of
quantum-gravity effects. However, the breakdown of spacetime symmetries has
recently been identified as a promising signal in this context: a number of
models for underlying physics can accommodate minuscule Lorentz and CPT
violation, and such effects are amenable to ultrahigh-precision tests. This
presentation will give an overview of the subject. Topics such as motivations,
the SME test framework, mechanisms for relativity breakdown, and experimental
tests will be reviewed. Emphasis is given to observations involving antimatter.Comment: 6 page
Can galaxy growth be sustained through HI-rich minor mergers?
Local galaxies with specific star-formation rates (star-formation rate per
unit mass; sSFR~0.2-10/Gyr) as high as distant galaxies (z~1-3), are very rich
in HI. Those with low stellar masses, log M_star (M_sun)=8-9, for example, have
M_HI/M_star~5-30. Using continuity arguments of Peng et al. (2014), whereby the
specific merger rate is hypothesized to be proportional to the specific
star-formation rate, and HI gas mass measurements for local galaxies with high
sSFR, we estimate that moderate mass galaxies, log M_star (M_sun)=9-10.5, can
acquire sufficient gas through minor mergers (stellar mass ratios ~4-100) to
sustain their star formation rates at z~2. The relative fraction of the gas
accreted through minor mergers declines with increasing stellar mass and for
the most massive galaxies considered, log M_star (M_sun)=10.5-11, this
accretion rate is insufficient to sustain their star formation. We checked our
minor merger hypothesis at z=0 using the same methodology but now with
relations for local normal galaxies and find that minor mergers cannot account
for their specific growth rates, in agreement with observations of HI-rich
satellites around nearby spirals. We discuss a number of attractive features,
like a natural down-sizing effect, in using minor mergers with extended HI
disks to support star formation at high redshift. The answer to the question
posed by the title, "Can galaxy growth be sustained through \HI-rich minor
mergers?", is maybe, but only for relatively low mass galaxies and at high
redshift.Comment: 6 pages, 3 figures; in final acceptance by A&
Estimate of heating effects in Raman microspectroscopy and the accuracy of stokes/anti-stokes thermometry
Нагрев образца значительно увеличивает неопределенность условий получения спектров в Рамановской микроспектроскопии. В работе теоретически оценен максимальный рост температуры внутри образца при воздействии лазерного излучения. Результат моделирования роста температуры представлен аналитически в виде функции свойств пробы (показатель рефракции, коэффициент абсорбции, теплопроводность), мощности лазера и значения апертуры фокусирующего объектива. Показано, что достигаемая точность определения температуры по соотношению интенсивностей стоксовской и антистоксовских полос может быть оценена теоретически, что имеет большую практическую значимость. Получена функциональная зависимость, связывающая точность определения температуры образца с основными источниками экспериментальных погрешностей. Обсуждены различные практически влияющие факторы, вызывающие ухудшение теоретического отношения dТ/Т
Conservation status and threats of Rallidae : a global assessment.
The avian family Rallidae is one of the most widespread avian families of the world. Rallidae greatly exceeds the other families within the order Gruiformes in sheer number of species, taxonomic complexity, geographical distribution, and ecological niche. At the time of this writing, there is no comprehensive, readily accessible, and up-to-date compilation of the conservation status of the world's rallids. This thesis provides a brief global overview of the status of rallids worldwide, focusing primarily on regional endemics and threatened species, and identifies the main threats and the associated particular knowledge gaps. The International Union for the Conservation of Nature (IUCN) Red List has a vast database of plants and animals found worldwide. The Red List Index (RLI) measures trends in regards to the risk of extinction; the data available for Rallidae species provides a broad measure of the overall population trend for some of the more cooperative, readily accessible, or targeted species. For many rallids, this is the only current trend indicator available on a regional or global basis. Data of avian families of similar size, equivalent global distributions, and similar lifestyles were also obtained from the RLI to compare for conservation status and population trends to place the circumstances of rallids in context; the families chosen were Anatidae, Cuculidae, Alcedinidae, and Corvidae. A chi-squared test showed significant (p<0.05) differences when comparing Rallidae population trends and conservation status to these four families. Listed threats to Rallidae were obtained from the IUCN and literature searches for the family and species listed as threatened. A chi-squared test showed a significant (p<0.05) number of insular species to have a threatened conservation status when compared to widespread species. Further focus was primarily on endemic and near-endemic species due to the inherent risk to these species as a result of their life history. Invasive species and habitat degradation or destruction were the primary threats identified. Wetland conservation is of special concern, as the majority of Rallidae species utilize this habitat. Internationally designated Important Bird Areas, Endemic Bird Areas, and associated sites designated under the Ramsar Convention were searched for mentions of rallids. In conclusion, Rallidae species are understudied and vast gaps in knowledge exist, particularly for species in remote locations and developing countries. The majority of rallids classified as Least Concern have decreasing or unknown population trends and should be reclassified as Data Deficient until more research is undertaken. The eradication of invasive species, particularly of mammalian predators, is essential to many endemic and near-endemic species recoveries. Habitat protections headed by BirdLife International and the Ramsar Convention are making headway worldwide, and with further research and environmental action the future of Rallidae is in turn better understood and protected
Dissecting the complex environment of a distant quasar with MUSE
High redshift quasars can be used to trace the early growth of massive
galaxies and may be triggered by galaxy-galaxy interactions. We present MUSE
science verification data on one such interacting system consisting of the
well-studied z=3.2 PKS1614+051 quasar, its AGN companion galaxy and bridge of
material radiating in Lyalpha between the quasar and its companion. We find a
total of four companion galaxies (at least two galaxies are new discoveries),
three of which reside within the likely virial radius of the quasar host,
suggesting that the system will evolve into a massive elliptical galaxy by the
present day. The MUSE data are of sufficient quality to split the extended
Lyalpha emission line into narrow velocity channels. In these the gas can be
seen extending towards each of the three neighbouring galaxies suggesting that
the emission-line gas originates in a gravitational interaction between the
galaxies and the quasar host. The photoionization source of this gas is less
clear but is probably dominated by the two AGN. The quasar's Lyalpha emission
spectrum is double-peaked, likely due to absorbing neutral material at the
quasar's systemic redshift with a low column density as no damping wings are
present. The spectral profiles of the AGN and bridge's Lyalpha emission are
also consistent with absorption at the same redshift indicating this neutral
material may extend over > 50 kpc. The fact that the neutral material is seen
in the line of sight to the quasar and transverse to it, and the fact that we
see the quasar and it also illuminates the emission-line bridge, suggests the
quasar radiates isotropically and any obscuring torus is small. These results
demonstrate the power of MUSE for investigating the dynamics of interacting
systems at high redshift.Comment: 9 pages, 6 figures, published in MNRA
Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit
We resolve phonon number states in the spectrum of a superconducting qubit
coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp
frequency dependence in the qubit-phonon interaction engineered by coupling the
qubit to surface acoustic waves in two locations separated by acoustic
wavelengths. In analogy to double-slit diffraction, the resulting
self-interference generates high-contrast frequency structure in the
qubit-phonon interaction. We observe this frequency structure both in the
coupling rate to multiple cavity modes and in the qubit spontaneous emission
rate into unconfined modes. We use this sharp frequency structure to resolve
single phonons by tuning the qubit to a frequency of destructive interference
where all acoustic interactions are dispersive. By exciting several detuned yet
strongly-coupled phononic modes and measuring the resulting qubit spectrum, we
observe that, for two modes, the device enters the strong dispersive regime
where single phonons are spectrally resolved.Comment: 9 pages, 8 figures; revised arguments in paragraphs 3 and 8, added
Hamiltonian description, and corrected typo
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