121 research outputs found
Impact of Resonance on Thermal Targets for Invisible Dark Photon Searches
Dark photons in the MeV to GeV mass range are important targets for
experimental searches. We consider the case where dark photons decay
invisibly to hidden dark matter through . For generic masses,
proposed accelerator searches are projected to probe the thermal target region
of parameter space, where the particles annihilate through in the early universe and freeze out with the correct relic density.
However, if , dark matter annihilation is resonantly
enhanced, shifting the thermal target region to weaker couplings. For degeneracies, we find that the annihilation cross section is generically
enhanced by four (two) orders of magnitude for scalar (pseudo-Dirac) dark
matter. For such moderate degeneracies, the thermal target region drops to weak
couplings beyond the reach of all proposed accelerator experiments in the
scalar case and becomes extremely challenging in the pseudo-Dirac case.
Proposed direct detection experiments can probe moderate degeneracies in the
scalar case. For greater degeneracies, the effect of the resonance can be even
more significant, and both scalar and pseudo-Dirac cases are beyond the reach
of all proposed accelerator and direct detection experiments. For scalar dark
matter, we find an absolute minimum that sets the ultimate experimental
sensitivity required to probe the entire thermal target parameter space, but
for pseudo-Dirac fermions, we find no such thermal target floor.Comment: 17 pages, 2 figures; v2: improved agreement with existing
non-resonant results, added extensive discussion of implications for direct
detection experiment
Dark Photons from the Center of the Earth: Smoking-Gun Signals of Dark Matter
Dark matter may be charged under dark electromagnetism with a dark photon
that kinetically mixes with the Standard Model photon. In this framework, dark
matter will collect at the center of the Earth and annihilate into dark
photons, which may reach the surface of the Earth and decay into observable
particles. We determine the resulting signal rates, including Sommerfeld
enhancements, which play an important role in bringing the Earth's dark matter
population to their maximal, equilibrium value. For dark matter masses 100 GeV - 10 TeV, dark photon masses MeV - GeV, and kinetic
mixing parameters , the resulting
electrons, muons, photons, and hadrons that point back to the center of the
Earth are a smoking-gun signal of dark matter that may be detected by a variety
of experiments, including neutrino telescopes, such as IceCube, and space-based
cosmic ray detectors, such as Fermi-LAT and AMS. We determine the signal rates
and characteristics, and show that large and striking signals---such as
parallel muon tracks---are possible in regions of the
plane that are not probed by direct detection, accelerator experiments, or
astrophysical observations.Comment: 26 pages, 10 figures. v2: minor revisions to match published version;
v3: updated direct detection and CMB constraints and corrected decay length
in code, moving the region of experimental sensitivity to values of epsilon
that are lower by an order of magnitud
An Explicit basis of lowering Operators for Irreducible Representations of Unitary Groups
The representation theory of the unitary groups is of fundamental significance in many areas of physics and chemistry. In order to label states in a physical system with unitary symmetry, it is necessary to have explicit bases for the irreducible representations. One systematic way of obtaining bases is to generalize the ladder operator approach to the representations of SU(2) by using the formalism of lowering operators. Here, one identifies a basis for the algebra of all lowering operators and, for each irreducible representation, gives a prescription for choosing a subcollection of lowering operators that yields a basis upon application to the highest weight vector. Bases obtained through lowering operators are particularly convenient for computing matrix coefficients of observables as the calculations reduce to the commutation relations for the standard matrix units. The best known examples of this approach are the extremal projector construction of the Gelfand-Zetlin basis and the crystal (or canonical) bases of Kashiwara and Lusztig. In this paper, we describe another simple method of obtaining bases for the irreducible representations via lowering operators. These bases do not have the algebraic canonicity of the Gelfand-Zetlin and crystal bases, but the combinatorics involved are much more straightforward, making the bases particularly suited for physical applications. © Lithuanian Physical Society, 2011
Protophobic Fifth-Force Interpretation of the Observed Anomaly in \u3csup\u3e8\u3c/sup\u3eBe Nuclear Transitions
Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e− pairs produced in 8Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be X, and then decays through X → e+e−. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon’s anomalous magnetic moment
Protophobic Fifth-Force Interpretation of the Observed Anomaly in \u3csup\u3e8\u3c/sup\u3eBe Nuclear Transitions
Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e− pairs produced in 8Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be X, and then decays through X → e+e−. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon’s anomalous magnetic moment
Swainson\u27s Thrushes Do Not Show Strong Wing Selectivity Prior to Crossing the Gulf of Mexico
During long-distance fall migrations, nocturnally migrating Swainson’s Thrushes often stop on the northern Gulf of Mexico coast before flying across the Gulf. To minimize energetic costs, trans-Gulf migrants should stop over when they encounter crosswinds or headwinds, and depart with supportive tailwinds. However, time constrained migrants should be less selective, balancing costs of headwinds with benefits of continuing their migrations. To test the hypotheses that birds select supportive winds and that selectivity is mediated by seasonal time constraints, we examined whether local winds affected Swainson’s Thrushes’ arrival and departure at Ft. Morgan, Alabama, USA at annual, seasonal, and nightly time scales. Additionally, migrants could benefit from forecasting future wind conditions, crossing on nights when winds are consistently supportive across the Gulf, thereby avoiding the potentially lethal consequences of depleting their energetic reserves over water. To test whether birds forecast, we developed a movement model, calculated to what extent departure winds were predictive of future Gulf winds, and tested whether birds responded to predictability. Swainson’s Thrushes were only slightly selective and did not appear to forecast. By following the simple rule of avoiding only the strongest headwinds at departure, Swainson’s Thrushes could survive the 1500 km flight between Alabama and Veracruz, Mexico
FASER: ForwArd Search ExpeRiment at the LHC
FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated to
searching for light, extremely weakly-interacting particles at the LHC. Such
particles may be produced in the LHC's high-energy collisions in large numbers
in the far-forward region and then travel long distances through concrete and
rock without interacting. They may then decay to visible particles in FASER,
which is placed 480 m downstream of the ATLAS interaction point. In this work,
we describe the FASER program. In its first stage, FASER is an extremely
compact and inexpensive detector, sensitive to decays in a cylindrical region
of radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructed
and installed in Long Shutdown 2 and will collect data during Run 3 of the 14
TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successor
with roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 and
collect data during the HL-LHC era from 2026-35. FASER and FASER 2 have the
potential to discover dark photons, dark Higgs bosons, heavy neutral leptons,
axion-like particles, and many other long-lived particles, as well as provide
new information about neutrinos, with potentially far-ranging implications for
particle physics and cosmology. We describe the current status, anticipated
challenges, and discovery prospects of the FASER program.Comment: 13 pages, 4 figures, submitted as Input to the European Particle
Physics Strategy Update 2018-2020 and draws on FASER's Letter of Intent,
Technical Proposal, and physics case documents (arXiv:1811.10243,
arXiv:1812.09139, and arXiv:1811.12522
Relationship among research collaboration, number of documents and number of citations. A case study in Spanish computer science production in 2000-2009.
This paper analyzes the relationship among research collaboration, number of documents and number of citations of computer science research activity. It analyzes the number of documents and citations and how they vary by number of authors. They are also analyzed (according to author set cardinality) under different circumstances, that is, when documents are written in different types of collaboration, when documents are published in different document types, when documents are published in different computer science subdisciplines, and, finally, when documents are published by journals with different impact factor quartiles. To investigate the above relationships, this paper analyzes the publications listed in the Web of Science and produced by active Spanish university professors between 2000 and 2009, working in the computer science field. Analyzing all documents, we show that the highest percentage of documents are published by three authors, whereas single-authored documents account for the lowest percentage. By number of citations, there is no positive association between the author cardinality and citation impact. Statistical tests show that documents written by two authors receive more citations per document and year than documents published by more authors. In contrast, results do not show statistically significant differences between documents published by two authors and one author. The research findings suggest that international collaboration results on average in publications with higher citation rates than national and institutional collaborations. We also find differences regarding citation rates between journals and conferences, across different computer science subdisciplines and journal quartiles as expected. Finally, our impression is that the collaborative level (number of authors per document) will increase in the coming years, and documents published by three or four authors will be the trend in computer science literature
Technical Proposal for FASER: ForwArd Search ExpeRiment at the LHC
FASER is a proposed small and inexpensive experiment designed to search for
light, weakly-interacting particles during Run 3 of the LHC from 2021-23. Such
particles may be produced in large numbers along the beam collision axis,
travel for hundreds of meters without interacting, and then decay to standard
model particles. To search for such events, FASER will be located 480 m
downstream of the ATLAS IP in the unused service tunnel TI12 and be sensitive
to particles that decay in a cylindrical volume with radius R=10 cm and length
L=1.5 m. FASER will complement the LHC's existing physics program, extending
its discovery potential to a host of new, light particles, with potentially
far-reaching implications for particle physics and cosmology.
This document describes the technical details of the FASER detector
components: the magnets, the tracker, the scintillator system, and the
calorimeter, as well as the trigger and readout system. The preparatory work
that is needed to install and operate the detector, including civil
engineering, transport, and integration with various services is also
presented. The information presented includes preliminary cost estimates for
the detector components and the infrastructure work, as well as a timeline for
the design, construction, and installation of the experiment.Comment: 82 pages, 62 figures; submitted to the CERN LHCC on 7 November 201
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