7,134 research outputs found
Searches for Sterile Neutrinos at Future Electron-Proton Colliders
Sterile neutrinos are an attractive extension of the Standard Model of
elementary particles towards including a mechanism for generating the observed
light neutrino masses. We discuss that when an approximate protective "lepton
number"-like symmetry is present, the sterile neutrinos can have masses around
the electroweak scale and potentially large neutrino Yukawa couplings, which
makes them well testable at planned future particle colliders. We
systematically discuss the production and decay channels for sterile neutrinos
at electron-proton colliders and give a complete list of the leading order
signatures for sterile neutrino searches. We highlight several novel search
channels and present a first look at the possible sensitivities for the
active-sterile mixing parameters and the heavy neutrino masses. We also compare
the performance of electron-proton colliders with the ones of proton-proton and
electron-positron colliders, and discuss the complementarity of the different
collider types.Comment: Conference proceedings for the DIS 2017 in Birmingham, 13 pages, 8
figures, 2 table
Combining states without scale hierarchies with ordered parton showers
We present a parameter-free scheme to combine fixed-order multi-jet results
with parton-shower evolution. The scheme produces jet cross sections with
leading-order accuracy in the complete phase space of multiple emissions,
resumming large logarithms when appropriate, while not arbitrarily enforcing
ordering on momentum configurations beyond the reach of the parton-shower
evolution equation. This requires the development of a matrix-element
correction scheme for complex phase-spaces including ordering conditions as
well as a systematic scale-setting procedure for unordered phase-space points.
The resulting algorithm does not require a merging-scale parameter. We
implement the new method in the Vincia framework and compare to LHC data.Comment: updated to version published in EPJ
Testing sterile neutrino extensions of the Standard Model at future lepton colliders
Extending the Standard Model (SM) with sterile ('right-handed') neutrinos is
one of the best motivated ways to account for the observed neutrino masses. We
discuss the expected sensitivity of future lepton collider experiments for
probing such extensions. An interesting testable scenario is given by 'symmetry
protected seesaw models', which theoretically allow for sterile neutrino masses
around the electroweak scale with up to order one mixings with the light (SM)
neutrinos. In addition to indirect tests, e.g. via electroweak precision
observables, sterile neutrinos with masses around the electroweak scale can
also be probed by direct searches, e.g. via sterile neutrino decays at the Z
pole, deviations from the SM cross section for four lepton final states at and
beyond the WW threshold and via Higgs boson decays. We study the present bounds
on sterile neutrino properties from LEP and LHC as well as the expected
sensitivities of possible future lepton colliders such as ILC, CEPC and FCC-ee
(TLEP).Comment: Version 2: typos fixed, references added, matches published versio
Sterile neutrino searches via displaced vertices at LHCb
We explore the sensitivity of displaced vertex searches at LHCb for testing
sterile neutrino extensions of the Standard Model towards explaining the
observed neutrino masses. We derive estimates for the constraints on sterile
neutrino parameters from a recently published displaced vertex search at LHCb
based on run 1 data. They yield the currently most stringent limit on
active-sterile neutrino mixing in the sterile neutrino mass range between 4.5
GeV and 10 GeV. Furthermore, we present forecasts for the sensitivities that
could be obtained from the run 2 data and also for the high-luminosity phase of
the LHC.Comment: 5 pages, 6 Figures, 1 Table, version to appear in PL
Uniformly Rotating Rings in General Relativity
In this paper, we discuss general relativistic, self-gravitating and
uniformly rotating perfect fluid bodies with a toroidal topology (without
central object). For the equations of state describing the fluid matter we
consider polytropic as well as completely degenerate, perfect Fermi gas models.
We find that the corresponding configurations possess similar properties to the
homogeneous relativistic Dyson rings. On the one hand, there exists no limit to
the mass for a given maximal mass-density inside the body. On the other hand,
each model permits a quasistationary transition to the extreme Kerr black hole.Comment: 6 pages, 4 figures, added material and one new referenc
Sterile neutrino searches at future , , and colliders
Sterile neutrinos are among the most attractive extensions of the SM to
generate the light neutrino masses observed in neutrino oscillation
experiments. When the sterile neutrinos are subject to a protective symmetry,
they can have masses around the electroweak scale and potentially large
neutrino Yukawa couplings, which makes them testable at planned future particle
colliders. We systematically discuss the production and decay channels at
electron-positron, proton-proton and electron-proton colliders and provide a
complete list of the leading order signatures for sterile neutrino searches.
Among other things, we discuss several novel search channels, and present a
first look at the possible sensitivities for the active-sterile mixings and the
heavy neutrino masses. We compare the performance of the different collider
types and discuss their complementarity.Comment: 20 pages + appendix + references, 21 figures, 10 Tables; added
references; extended discussion of displaced vertex searches at pp an ep
collider
Displaced vertex searches for sterile neutrinos at future lepton colliders
We investigate the sensitivity of future lepton colliders to displaced
vertices from the decays of long-lived heavy (almost sterile) neutrinos with
electroweak scale masses and detectable time of flight. As future lepton
colliders we consider the FCC-ee, the CEPC, and the ILC, searching at the
Z-pole and at the center-of-mass energies of 240, 350 and 500 GeV. For a
realistic discussion of the detector response to the displaced vertex signal
and the Standard Model background we consider the ILC's Silicon Detector (SiD)
as benchmark for the future lepton collider detectors. We find that displaced
vertices constitute a powerful search channel for sterile neutrinos, sensitive
to squared active-sterile mixing angles as small as .Comment: 13 pages plus references, 8 figures, 1 table, matches published
versio
Higgs production from sterile neutrinos at future lepton colliders
In scenarios with sterile (right-handed) neutrinos that are subject to an
approximate "lepton-number-like" symmetry, the heavy neutrinos (i.e. the mass
eigenstates) can have masses around the electroweak scale and couple to the
Higgs boson with, in principle, unsuppressed Yukawa couplings while accounting
for the smallness of the light neutrinos' masses. In these scenarios, the
on-shell production of heavy neutrinos and their subsequent decays into a light
neutrino and a Higgs boson constitutes a hitherto unstudied resonant
contribution to the Higgs production mechanism. We investigate the relevance of
this resonant mono-Higgs production mechanism in leptonic collisions, including
the present experimental constraints on the neutrino Yukawa couplings, and we
determine the sensitivity of future lepton colliders to the heavy neutrinos.
With Monte Carlo event sampling and a simulation of the detector response we
find that, at future lepton colliders, neutrino Yukawa couplings below the
percent level can lead to observable deviations from the SM and, furthermore,
the sensitivity improves with higher center-of-mass energies (for identical
integrated luminosities).Comment: 26 pages, 9 figures, 7 tables; v2: references adde
Low scale type II seesaw: Present constraints and prospects for displaced vertex searches
The type II seesaw mechanism is an attractive way to generate the observed
light neutrino masses. It postulates a SU(2)-triplet scalar field,
which develops an induced vacuum expectation value after electroweak symmetry
breaking, giving masses to the neutrinos via its couplings to the lepton
SU(2)-doublets. When the components of the triplet field have
masses around the electroweak scale, the model features a rich phenomenology.
We discuss the current allowed parameter space of the minimal low scale type II
seesaw model, taking into account all relevant constraints, including charged
lepton flavour violation as well as collider searches. We point out that the
symmetry protected low scale type II seesaw scenario, where an approximate
"lepton number"-like symmetry suppresses the Yukawa couplings of the triplet to
the lepton doublets, is still largely untested by the current LHC results. In
part of this parameter space the triplet components can be long-lived,
potentially leading to a characteristic displaced vertex signature where the
doubly-charged component decays into same-sign charged leptons. By performing a
detailed analysis at the reconstructed level we find that already at the
current run of the LHC a discovery would be possible for the considered
parameter point, via dedicated searches for displaced vertex signatures. The
discovery prospects are further improved at the HL-LHC and the FCC-hh/SppC.Comment: 21 pages, 10 figures, 1 tabl
Revisiting Radiation Patterns in Collisions
We propose four simple event-shape variables for semi-inclusive -jet events. The observables and cuts are designed to be especially sensitive
to subleading aspects of the event structure, and allow to test the reliability
of phenomenological QCD models in greater detail. Three of them, ,
, and , focus on soft emissions off three-jet topologies
with a small opening angle, for which coherence effects beyond the leading QCD
dipole pattern are expected to be enhanced. A complementary variable,
, measures the ratio of the hemisphere masses in 4-jet events with
a compressed scale hierarchy (Durham ), for which subleading
splitting effects are expected to be enhanced. We consider several
different parton-shower models, spanning both conventional and dipole/antenna
ones, all tuned to the same reference data, and show that a
measurement of the proposed observables would allow for additional significant
discriminating power between the models.Comment: 27 pages, 10 figure
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