The νMSM,inflation, and dark matter

We show how to enlarge the νMSM (the minimal extension of the Standard Model by three right-handed neutrinos) to incorporate inflation and provide a common source for electroweak symmetry breaking and for right-handed neutrino masses. In addition to inflation, the resulting theory can explain simultaneously dark matter and the baryon asymmetry of the Universe; it is consistent with experiments on neutrino oscillations and with all astrophysical and cosmological constraints on sterile neutrino as a dark matter candidate. The mass of inflaton can be much smaller than the electroweak scale.     

Relic keV sterile neutrinos and reionization

A sterile neutrino with a mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that x rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the Universe at a high enough redshift to be consistent with the Wilkinson Microwave Anisotropy Probe results.     

Magnetic dipole moment and keV neutrino dark matter

We study magnetic dipole moments of right-handed neutrinos in a keV neutrino dark matter model. This model is a simple extension of the standard model with only right-handed neutrinos and a pair of charged particles added. One of the right-handed neutrinos is the candidate of dark matter with a keV mass. Some bounds on the dark matter magnetic dipole moment and model parameters are obtained from cosmological observations.     

Efficient coannihilation process through strong Higgs self-coupling in LKP dark matter annihilation

We point out that the lightest Kaluza–Klein particle (LKP) dark matter in universal extra dimension (UED) models efficiently annihilates through the coannihilation process including the first KK Higgs bosons when the Higgs mass is slightly heavy as 200–230 GeV, which gives the large Higgs self-coupling. The large self-coupling naturally leads the mass degeneracy between the LKP and the first KK Higgs bosons and large annihilation cross sections of the KK Higgs bosons. These are essential for the enhancement of the annihilation of the LKP dark matter, which allows large compactification scale ∼1 TeV to be consistent with cosmological observations for the relic abundance of dark matter. We found that the thermal relic abundance of the LKP dark matter could be reconciled with the stringent constraint of electroweak precision measurements in the minimal UED model.     

Unified picture for Dirac neutrinos,dark matter,dark energy and matter–antimatter asymmetry

We propose a unified scenario to generate the masses of Dirac neutrinos and cold dark matter at the TeV scale, understand the origin of dark energy and explain the matter–antimatter asymmetry of the universe. This model can lead to significant impact on the Higgs searches at LHC.     

Low reheating temperature and the visible sterile neutrino

We present here a scenario, based on a low reheating temperature T(R)<100 MeV at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino "visible" in future experiments). In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. Here the abundance depends on how low the reheating temperature is. For example, the sterile neutrino required by the Liquid Scintillator Neutrino Detector result may not have any cosmological problem within our scenario.     

Reconciling cold dark matter with COBE/IRAS plus solar and atmospheric neutrino data

We present a model where an unstable MeV Majorana tau neutrino can naturally reconcile the cold dark matter model (CDM) with cosmological observations of large and small scale density fluctuations and, simultaneously, with data on solar and atmospheric neutrinos. The solar neutrino deficit is explained through long wavelength, so-called just-so oscillations involving conversions of ν_e into both ν_μ and a sterile species ν_s , while atmospheric neutrino data are explained through ν_μ to ν_e conversions. Future long baseline neutrino oscillation experiments, as well as some reactor experiments will test this hypothesis. The model is based on the spontaneous violation of a global lepton number symmetry at the weak scale. This symmetry plays a key role in generating the cosmologically required decay of the ν_τ with lifetime τ_ντ ≈ 10²-10⁴ seconds, as well as the masses and oscillations of the three light neutrinos ν_e, ν_μ and ν_s required in order to account for solar and atmospheric neutrino data. It also leads to the invisibly decaying Higgs signature that can be searched at LEP and future particle colliders.     

Particle Physics and Cosmology

Observational tests of cosmological theories are reviewed, with emphasis on the cosmological microwave background (CMB) radiation and dark matter. Present observations of the CMB are consistent with inflationary models, that have already excluded some alternatives. Particle dark matter candidates are reviewed, including massive neutrinos, the lightest supersymmetric particle (LSP), ultra-heavy relics from the Big Bang, and cosmological vacuum energy. Finally, some personal guesses at confidence ratings are hazarded.     

A search for sterile neutrinos with the latest cosmological observations

We report the result of a search for sterile neutrinos with the latest cosmological observations. Both cases of massless and massive sterile neutrinos are considered in the \(\Lambda \)CDM cosmology. The cosmological observations used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation data, the Hubble constant direct measurement data, the Planck Sunyaev–Zeldovich cluster counts data, the Planck lensing data, and the cosmic shear data. We find that the current observational data give a hint of the existence of massless sterile neutrino (as dark radiation) at the 1.44\(\sigma \) level, and the consideration of an extra massless sterile neutrino can indeed relieve the tension between observations and improve the cosmological fit. For the case of massive sterile neutrino, the observations give a rather tight upper limit on the mass, which implies that actually a massless sterile neutrino is more favored. Our result is consistent with the recent result of neutrino oscillation experiment done by the Daya Bay and MINOS collaborations, as well as the recent result of cosmic ray experiment done by the IceCube collaboration.     

Constraints on composite Dirac neutrinos from observations of galaxy clusters

Recently, to explain the origin of neutrino masses a model based on confining some hidden fermionic bound states into right-handed chiral neutrinos has been proposed. One of the consequences of condensing the hidden sector fields in this model is the presence of sterile composite Dirac neutrinos of keV mass, which can form viable warm dark matter particles. We have analyzed constraints on this model from the observations of satellite based telescopes to detect the sterile neutrinos in clusters of galaxies.     

Late time neutrino masses, the LSND experiment, and the cosmic microwave background

Models with low-scale breaking of global symmetries in the neutrino sector provide an alternative to the seesaw mechanism for understanding why neutrinos are light. Such models can easily incorporate light sterile neutrinos required by the Liquid Scintillator Neutrino Detector experiment. Furthermore, the constraints on the sterile neutrino properties from nucleosynthesis and large-scale structure can be removed due to the nonconventional cosmological evolution of neutrino masses and densities. We present explicit, fully realistic supersymmetric models, and discuss the characteristic signatures predicted in the angular distributions of the cosmic microwave background.     

Testing a new sterile neutrino dark matter candidate

A new class of sterile neutrino dark matter is suggested by an explanation for time variations in the solar neutrino flux in which coupling of sterile neutrinos to other matter is via a very small flavor off-diagonal transition magnetic moment, TMM. The dark matter sterile neutrino’s decay in the radiative channel then depends on the local magnetic field and the unknown value of the TMM. An interesting application of this model uses the DAMA/LIBRA claimed detection of dark matter (assuming they are observing the electromagnetic signal) to provide the decay rate in the Earth’s field, and hence the TMM value. That version of the model is then examined to see if it can be falsified by cosmic X-ray observations or by other direct detection experiments. Particularly the latter could provide a simple, definitive test of this dark matter candidate, which would bring concordance to these experiments.     

Entropy, baryon asymmetry and dark matter from heavy neutrino decays

The origin of the hot phase of the early universe remains so far an unsolved puzzle. A viable option is entropy production through the decays of heavy Majorana neutrinos whose lifetimes determine the initial temperature. We show that baryogenesis and the production of dark matter are natural by-products of this mechanism. As is well known, the cosmological baryon asymmetry can be accounted for by leptogenesis for characteristic neutrino mass parameters. We find that thermal gravitino production then automatically yields the observed amount of dark matter, for the gravitino as the lightest superparticle and typical gluino masses. As an example, we consider the production of heavy Majorana neutrinos in the course of tachyonic preheating associated with spontaneous B−L breaking. A quantitative analysis leads to constraints on the superparticle masses in terms of neutrino masses: For a light neutrino mass of ¹⁰−5 eV the gravitino mass can be as small as 200 MeV, whereas a lower neutrino mass bound of 0.01 eV implies a lower bound of 9 GeV on the gravitino mass. The measurement of a light neutrino mass of 0.1 eV would rule out heavy neutrino decays as the origin of entropy, visible and dark matter.     

Masses of active neutrinos in the νMSM from x-ray astronomy

In an extension of the Standard Model by three relatively light right-handed neutrinos (the νMSM model) the role of the dark matter particle is played by the lightest sterile neutrino. We demonstrate that the observations of the extragalactic x-ray background allow us to put a strong upper bound on the mass of the lightest active neutrino and predict the absolute values of the mass of the two heavier active neutrinos in the νMSM provided that the mass of the dark matter sterile neutrino is larger than 1.8 keV. The text was submitted by the authors in English.     

Can sterile neutrinos be ruled out as warm dark matter candidates?

We present constraints on the mass of warm dark matter (WDM) particles from a combined analysis of the matter power spectrum inferred from the Sloan Digital Sky Survey Lyman-alpha flux power spectrum at 2.2相似文献   

Neutrino oscillations as a probe of dark energy

We consider a class of theories in which neutrino masses depend significantly on environment, as a result of interactions with the dark sector. Such theories of mass varying neutrinos were recently introduced to explain the origin of the cosmological dark energy density and why its magnitude is apparently coincidental with that of neutrino mass splittings. In this Letter we argue that in such theories neutrinos can exhibit different masses in matter and in vacuum, dramatically affecting neutrino oscillations. As an example of modifications to the standard picture, we consider simple models that may simultaneously account for the LSND anomaly, KamLAND, K2K, and studies of solar and atmospheric neutrinos, while providing motivation to continue to search for neutrino oscillations in short baseline experiments such as BooNE.     

Extending the MSSM with Singlet Higgs and Right Handed Neutrino for the Self-Interacting Dark Matter

In order to meet the requirement of BBN,the right handed neutrino is added to the singlet Higgs sector in the GNMSSM.The spectrum and Feynman rules are calculated.the dark matter pheonomenology is also studied.In case of λ ~ 0,the singlet sector can give perfect explanation of relic abundance of dark matter and small cosmological structure simulations.The BBN constraints on the light mediator can be easily solved by decaying to the right handed neutrino.When the λ_N is at the order of O(0.1),the mass of the mediator can be constrained to several MeV.     

Status of the scalar singlet dark matter model

One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a \(\mathbb {Z}_2\) symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above \(\sim \)1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.     

Testing the mechanism for the LSP stability at the LHC

The lightest supersymmetric particle (LSP) is a natural candidate for the cold dark matter of the universe. In this Letter we discuss how to test the mechanism responsible for the LSP stability at the LHC. We note that if R-parity is conserved dynamically one should expect a Higgs boson which decays mainly into two right-handed neutrinos (a “leptonic” Higgs) or into two sfermions. The first case could exhibit spectacular lepton number violating signals with four secondary vertices due to the long-lived nature of right-handed neutrinos. These signals, together with the standard channels for the discovery of SUSY, could help to establish the underlying theory at the TeV scale.