In this paper we investigate the phenomenology of a very light scalar, h, with mass 100 MeV < m h < 10 GeV, mixing with the SM Higgs. As a benchmark model we take the real singlet scalar extension of the SM. We point out apparently unresolved uncertainties in the branching ratios and lifetime of h in a crucial region of parameter space for LHC phenomenology. Bounds from LEP, meson decays and fixed target experiments are reviewed. We also examine prospects at the LHC. For m h m B the dominant production mechanism is via meson decay; our main result is the calculation of the differential p T spectrum of h scalars originating from B mesons and the subsequent prediction of up to thousands of moderate (triggerable) p T displaced dimuons possibly hiding in the existing dataset at ATLAS/CMS or at LHCb. We also demonstrate that the subdominant V h production channel has the best sensitivity for m h m B and that future bounds in this region could conceivably compete with those of LEP.
The Large Hadron Collider provides us new opportunities to search for the origin of neutrino mass. Beyond the minimal see-saw models a plethora of models exist which realise neutrino mass at tree-or loop-level, and it is important to be sure that these possibilities are satisfactorily covered by searches. The purpose of this paper is to advance a systematic approach to this problem. Majorana neutrino mass models can be organised by SM-gauge-invariant operators which violate lepton number by two units. In this paper we write down the minimal ultraviolet completions for all of the mass-dimension 7 operators. We predict vector-like quarks, vector-like leptons, scalar leptoquarks, a charged scalar, a scalar doublet, and a scalar quadruplet, whose properties are constrained by neutrino oscillation data. A detailed collider study is presented for O 3 = LLQdH and O 8 = Ldē †ū † H completions with a vector-like quark χ ∼ (3, 2, − 5 6 ) and a leptoquark φ ∼ (3, 1, 1 3 ). The existing LHC limits extracted from searches for vector-like fermions and sbottoms/stops are m χ 620 GeV and m φ 600 GeV.
The minimal Type I see-saw model cannot explain the observed neutrino masses and the baryon asymmetry of the Universe via hierarchical thermal leptogenesis without ceding naturalness. We show that this conclusion can be avoided by adding a second Higgs doublet with tan β 4. The models considered naturally accommodate a SM-like Higgs boson, and predict TeV-scale scalar states and low-to intermediate-scale hierarchical leptogenesis with 10 3 GeV MN 1 10 8 GeV.
In the Type I see-saw model, the naturalness requirement that corrections to the electroweak µ parameter not exceed 1 TeV results in a rough bound on the lightest right-handed neutrino mass, MN 1 3 × 10 7 GeV. In this letter we derive generic bounds applicable in any three-flavour Type I see-saw model. We find MN 1 4 × 10 7 GeV and MN 2 7 × 10 7 GeV. In the limit of one massless neutrino, there is no naturalness bound on MN 3 in the Poincaré protected decoupling limit. Our results confirm that no Type I see-saw model can explain the observed neutrino masses and baryogenesis via hierarchical (N1-, N2-, or N3-dominated) thermal leptogenesis while remaining completely natural.
We describe a minimal extension of the standard model by three right-handed neutrinos, a scalar doublet, and a scalar singlet (the "νDFSZ") which serves as an existence proof that weakly coupled high-scale physics can naturally explain phenomenological shortcomings of the SM. The νDFSZ can explain neutrino masses, baryogenesis, the strong CP problem, and dark matter, and remains calculably natural despite a hierarchy of scales up to ∼ 10 11 GeV. It predicts a SM-like Higgs boson, (maximally) TeV-scale scalar states, intermediate-scale hierarchical leptogenesis (10 5 GeV MN 10 7 GeV), and axionic dark matter.
Dark matter in spiral galaxies like the Milky Way may take the form of a dark plasma. Hidden sector dark matter charged under an unbroken U (1) gauge interaction provides a simple and well defined particle physics model realising this possibility. The assumed U (1) neutrality of the Universe then implies (at least) two oppositely charged dark matter components with self-interactions mediated via a massless "dark photon" (the U (1) gauge boson). In addition to nuclear recoils such dark matter can give rise to keV electron recoils in direct detection experiments. In this context, the detailed physical properties of the dark matter plasma interacting with the Earth is required. This is a complex system, which is here modelled as a fluid governed by the magnetohydrodynamic equations. These equations are numerically solved for some illustrative examples, and implications for direct detection experiments discussed. In particular, the analysis presented here leaves open the intriguing possibility that the DAMA annual modulation signal is due primarily to electron recoils (or even a combination of electron recoils and nuclear recoils). The importance of diurnal modulation (in addition to annual modulation) as a means of probing this kind of dark matter is also emphasised.
Nanoporous gold and silver exhibit strong, omnidirectional broad-band absorption in the far-field. Even though they consist entirely of gold or silver atoms, these materials appear black and dull, in great contrast with the familiar luster of continuous gold and silver. The nature of these anomalous optical characteristics is revealed here by combining nanoscale electron energy loss spectroscopy with discrete dipole and boundary element simulations. It is established that the strong broad-band absorption finds its origin in nanoscale splitting of light, with great local variations in the absorbed color. This nanoscale polychromaticity results from the excitation of localized surface plasmon resonances, which are imaged and analyzed here with deep sub-wavelength, nanometer spatial resolution. We demonstrate that, with this insight, it is possible to customize the absorbance and reflectance wavelength bands of thin nanoporous films by only tuning their morphology.
Mirror dark matter, where dark matter resides in a hidden sector exactly isomorphic to the standard model, can be probed via direct detection experiments by both nuclear and electron recoils if the kinetic mixing interaction exists. In fact, the kinetic mixing interaction appears to be a prerequisite for consistent small scale structure: Mirror dark matter halos around spiral galaxies are dissipative - losing energy via dark photon emission. This ongoing energy loss requires a substantial energy input, which can be sourced from ordinary supernovae via kinetic mixing induced processes in the supernova's core. Astrophysical considerations thereby give a lower limit on the kinetic mixing strength, and indeed lower limits on both nuclear and electron recoil rates in direct detection experiments can be estimated. We show here that potentially all of the viable parameter space will be probed in forthcoming XENON experiments including LUX and XENON1T. Thus, we anticipate that these experiments will provide a definitive test of the mirror dark matter hypothesis.Comment: about 10 page
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.