Additional Neutrino Research Articles

Natural SUSY at LHC with right-sneutrino LSP

We study an extension of the minimal supersymmetric standard model (MSSM) with additional right-handed singlet neutrino superfields. While such an extension incorporates a mechanism for the neutrino mass, it also opens up the possibility of having the right-sneutrinos ( tilde{nu} ) as the lightest supersymmetric particle (LSP). In this work, we focus on the viability of rather small (≲500 GeV) higgsino mass parameter (μ), an important ingredient for “naturalness”, in the presence of such a LSP. For simplicity, we assume that the bino and wino mass parameters are much heavier; thus we only consider (almost) pure and compressed higgsino-like states, with small mathcal{O}left(1{0}^{-2}right) gaugino admixture which nevertheless still affect the decay of the low-lying higgsino-like states, thus significantly affecting the proposed signatures at colliders. Considering only prompt decays of the higgino-like states, especially the lightest chargino, we discuss the importance of leptonic channels consisting of up to two leptons with large missing transverse energy to probe this scenario at the Large Hadron Collider (LHC). In addition we also comment on the dark matter predictions for the studied scenario.

Effects of Fallback Accretion on Protomagnetar Outflows in Gamma-Ray Bursts and Superluminous Supernovae

Abstract Rapidly spinning, strongly magnetized protoneutron stars (“millisecond protomagnetars”) are candidate central engines of long-duration gamma-ray bursts (GRBs), superluminous supernovae (SLSNe), and binary neutron star mergers. Magnetar birth may be accompanied by the fallback of stellar debris, lasting for seconds or longer following the explosion. Accretion alters the magnetar evolution by (1) providing an additional source of rotational energy (or a potential sink, if the propeller mechanism operates), (2) enhancing the spin-down luminosity above the dipole rate by compressing the magnetosphere and expanding the polar cap region of open magnetic field lines, and (3) supplying an additional accretion-powered neutrino luminosity that sustains the wind baryon loading, even after the magnetar’s internal neutrino luminosity has subsided. The more complex evolution of the jet power and magnetization of an accreting magnetar more readily accounts for the high 56Ni yields of GRB SNe and the irregular time evolution of some GRB light curves (e.g., bursts with precursors followed by a long quiescent interval before the main emission episode). Additional baryon loading from accretion-powered neutrino irradiation of the polar cap lengthens the time frame over which the jet magnetization is in the requisite range σ ≲ 103 for efficient gamma-ray emission, thereby accommodating GRBs with ultralong durations. Though accretion does not significantly raise the maximum energy budget from the limit of ≲ few × 1052 erg for an isolated magnetar, it greatly expands the range of magnetic field strengths and birth spin periods capable of powering GRB jets, reducing the differences between the magnetar properties normally invoked to explain GRBs versus SLSNe.

Jet substructure shedding light on heavy Majorana neutrinos at the LHC

The existence of tiny neutrino masses and flavor mixings can be explained naturally in various seesaw models, many of which typically having additional Majorana type SM gauge singlet right handed neutrinos (N). If they are at around the electroweak scale and furnished with sizable mixings with light active neutrinos, they can be produced at high energy colliders, such as the Large Hadron Collider (LHC). A characteristic signature would be same sign lepton pairs, violating lepton number, together with light jets — pp → Nℓ±, N → ℓ±W∓, W∓ → jj. We propose a new search strategy utilising jet substructure techniques, observing that for a heavy right handed neutrino mass MN much above MW ±, the two jets coming out of the boosted W± may be interpreted as a single fat-jet (J). Hence, the distinguishing signal topology will be ℓ±ℓ±J . Performing a comprehensive study of the different signal regions along with complete background analysis, in tandem with detector level simulations, we compute statistical significance limits. We find that heavy neutrinos can be explored effectively for mass ranges 300 GeV ≤ MN ≤ 800 GeV and different light-heavy neutrino mixing |VμN|2. At the 13 TeV LHC with 3000 fb−1 integrated luminosity one can competently explore mixing angles much below present LHC limits, and moreover exceed bounds from electroweak precision data.

Conformal Standard Model and Inflation

This article presents a possible inflation scenario as a consequence of non-minimal gravitational couplings in the Conformal Standard Model. The model consists, in comparison to the SM, of additional right-chiral neutrinos and complex scalars coupled to the right-chiral neutrinos but not to the SM particles. The inflation is driven by two non-minimally coupled fields one being the usual Higgs and the other one of the sterile scalars. It turns out that in this model the tensor to scalar ratio and spectral index can match the current data for a wide range of parameters.

Anomalies in (semi)-leptonic B decays B±→τ±ν, B±→Dτ±ν and B±→D*τ±ν, and possible resolution with sterile neutrino**G.C. acknowledges the support by FONDECYT (Chile) (1130599), The work of C.S.K. was supported in part by the NRF grant funded by the Korean government of the MEST (2016R1D1A1A02936965)

The universality of the weak interactions can be tested in semileptonic b→c transitions, and in particular in the ratios R(D(*)) ≡ Γ(B→D(*)τν)/Γ(B→D(*)lν) (where l=μ or e). Due to the recent differences between the experimental measurements of these observables by BaBar, Belle and LHCb on the one hand and the Standard Model predicted values on the other hand, we study the predicted ratios R(D(*))=Γ(B→D(*)τ+“missing”)/Γ(B→D(*)lν) in scenarios with an additional sterile heavy neutrino of mass ∼1 GeV. Further, we evaluate the newly defined ratio R(0)≡Γ(B→τ+“missing”)/Γ(B→μν) in such scenarios, in view of the future possibilities of measuring the quantity at Belle-II.

Search for short-baseline oscillations at the NOvA Near Detector

Anomalous results from past neutrino experiments have been interpreted as potential evidence for an additional sterile neutrino with a mass on order of 1 eV, but this evidence remains inconclusive. The NOvA Near Detector is a 300 ton almost fully-active fine-grained liquid scintillator detector, that was designed for electron-neutrino identification. The detector is placed along the Fermilab NuMI beam line 1 km from the target and 14.6 mrad off-axis. At this off-axis angle the detector is exposed to a narrow band beam peaked at 2 GeV. Therefore the NOvA Near Detector will see neutrinos with a L/E range that is sensitive to oscillations between active neutrinos and light sterile neutrinos. In this report we discuss NOvA sensitivity from the joint electron-neutrino appearance and muon-neutrino disappearance analysis search for short-baseline sterile neutrino mixing.

A search for sterile neutrinos with IceCube DeepCore

The DeepCore detector is a densely instrumented part of the IceCube Neutrino Observatory that lowers the neutrino detection threshold down to approximately 10 GeV resulting in the ability to measure atmospheric neutrino oscillations. The standard three neutrino mixing scenario can be tested by searching for an additional light sterile neutrino state, which does not interact via the standard weak interaction, but mixes with the three active neutrino states. This leads to an impact on the atmospheric neutrino oscillations below 100 GeV. We present improved limits to the sterile mixing element |Uτ4|2 using three years of the DeepCore data taken during 2011-2013.

Axion and neutrino physics in aU(1)-enhanced supersymmetric model

Motivated by the flavored Peccei-Quinn symmetry for unifying the flavor physics and string theory, we construct an explicit model by introducing a $U(1)$ symmetry such that the $U(1)_X$-$[gravity]^2$ anomaly-free condition together with the standard model flavor structure demands additional sterile neutrinos as well as no axionic domain-wall problem. Such additional sterile neutrinos play the role of a realization of baryogenesis via a new Affleck-Dine leptogenesis. We provide grounds for that the $U(1)_X$ symmetry could be interpreted as a fundamental symmetry of nature. The model will resolve rather recent, but fast-growing issues in astro-particle physics, including leptonic mixings and CP violation in neutrino oscillation, high-energy neutrinos, QCD axion, and axion cooling of stars. The QCD axion decay constant, through its connection to the astrophysical constraints of stellar evolution and the SM fermion masses, is shown to be fixed at $F_A=1.30^{+0.66}_{-0.54}\times10^{9}$ GeV (consequently, its mass is $m_a=4.34^{+3.37}_{-1.49}$ meV and axion-photon coupling is $|g_{a\gamma\gamma}|=1.30^{+1.01}_{-0.45}\times10^{-12}\,{\rm GeV}^{-1}$). Interestingly enough, we show that neutrino oscillations at low energies could be connected to astronomical-scale baseline neutrino oscillations. The model predicts non-observational neutrinoless double beta ($0\nu\beta\beta$) decay rate as well as a remarkable pattern between leptonic Dirac CP phase ($\delta_{CP}$) and atmospheric mixing angle ($\theta_{23}$); {\it e.g.} $\delta_{CP}\simeq220^{\circ}-240^{\circ}$, $120^{\circ}-140^{\circ}$ for $\theta_{23}=42.3^{\circ}$ for normal mass ordering, and $\delta_{CP}\simeq283^{\circ},250^{\circ},100^{\circ},70^{\circ}$ for $\theta_{23}=49.5^{\circ}$ for inverted one.

Higgsino-like dark matter from sneutrino late decays

We consider Higgsino-like dark matter (DM) in the Minimal Supersymmetric Standard Model (MSSM) with additional right-handed neutrino chiral superfields, and propose a new non-thermal way of generating the right amount of relic DM via sneutrino late decays. Due to the large DM annihilation cross-section, decays must occur at lower temperatures than the freeze-out temperature Td≪TF,χ˜10∼μ/25, implying a mostly right-handed lightest sneutrino with very small Yukawa interactions. In that context, the right amount of Higgsino-like DM relic density can be accounted for if sneutrinos are produced via thermal freeze-in in the early Universe.

Cosmology based on f(R) gravity with O(1)eV sterile neutrino

We confront different up to date cosmological data with different gravity models of the Universe with one additional massive sterile neutrino [1].

Obscured flat spectrum radio active galactic nuclei as sources of high-energy neutrinos

Active Galactic Nuclei (AGN) are believed to be one of the main source candidates for the high-energy (TeV-PeV) cosmic neutrino flux recently discovered by the IceCube neutrino observatory. Nevertheless, several correlation studies between AGN and the cosmic neutrinos detected by IceCube show no significance. Therefore, in this article we consider a specific sub-class of AGN for which an increased neutrino production is expected. This sub-class contains AGN for which their high-energy jet is pointing toward Earth. Furthermore, we impose the condition that the jet is obscured by gas or dust surrounding the AGN. A method is presented to determine the total column density of the obscuring medium, which is probed by determining the relative X-ray attenuation with respect to the radio flux as obtained from the AGN spectrum. The total column density allows us to probe the interaction of the jet with the surrounding matter which leads to additional neutrino production. Finally, starting from two different source catalogs, this method is applied to specify a sample of low redshift radio galaxies for which an increased neutrino production is expected.

νμ → ν e oscillations search in the OPERA experiment

The tracking capabilities of the OPERA detector allow to reconstruct τ-leptons and electrons. It gives a possibility to observe νμ → ντ oscillations in the appearance mode and to study νμ → νe oscillations in the νμ CNGS beam. Current results on νμ → νe channel in the three-flavour mixing model are presented. The same data allow to constrain the presence of additional sterile neutrino states. The analysis of the full 2008–2012 OPERA data set and work on its improvement are going on. Details of the achievements are presented.

Hierarchy spectrum of SM fermions: from top quark to electron neutrino

In the SM gauge symmetries and fermion content of neutrinos, charged leptons and quarks, we study the effective four-fermion operators of Einstein-Cartan type and their contributions to the Schwinger-Dyson equations of fermion self-energy functions. The study is motivated by the speculation that these four-fermion operators are probably originated due to the quantum gravity that provides the natural regularization for chiral-symmetric gauge field theories. In the chiral-gauge symmetry breaking phase, as to achieve the energetically favorable ground state, only the top-quark mass is generated via the spontaneous symmetry breaking, and other fermion masses are generated via the explicit symmetry breaking induced by the top-quark mass, four-fermion interactions and fermion-flavor mixing matrices. A phase transition from the symmetry breaking phase to the chiral-gauge symmetric phase at TeV scale occurs and the drastically fine-tuning problem can be resolved. In the infrared fixed-point domain of the four-fermion coupling for the SM at low energies, we qualitatively obtain the hierarchy patterns of the SM fermion Dirac masses, Yukawa couplings and family-flavor mixing matrices with three additional right-handed neutrinos $\nu^f_R$. Large Majorana masses and lepton-symmetry breaking are originated by the four-fermion interactions among $\nu^f_R$ and their left-handed conjugated fields $\nu^{fc}_R$. Light masses of gauged Majorana neutrinos in the normal hierarchy ($10^{-5}-10^{-2}$ eV) are obtained consistently with neutrino oscillations. We present some discussions on the composite Higgs phenomenology and forward-backward asymmetry of $t\bar t$-production, as well as remarks on the candidates of light and heavy dark matter particles (fermions, scalar and pseudoscalar bosons).

A consistent model for leptogenesis, dark matter and the IceCube signal

We discuss a left-right symmetric extension of the Standard Model in which the three additional right-handed neutrinos play a central role in explaining the baryon asymmetry of the Universe, the dark matter abundance and the ultra energetic signal detected by the IceCube experiment. The energy spectrum and neutrino flux measured by IceCube are ascribed to the decays of the lightest right-handed neutrino $N_1$, thus fixing its mass and lifetime, while the production of $N_1$ in the primordial thermal bath occurs via a freeze-in mechanism driven by the additional $SU(2)_R$ interactions. The constraints imposed by IceCube and the dark matter abundance allow nonetheless the heavier right-handed neutrinos to realize a standard type-I seesaw leptogenesis, with the $B-L$ asymmetry dominantly produced by the next-to-lightest neutrino $N_2$. Further consequences and predictions of the model are that: the $N_1$ production implies a specific power-law relation between the reheating temperature of the Universe and the vacuum expectation value of the $SU(2)_R$ triplet; leptogenesis imposes a lower bound on the reheating temperature of the Universe at $7\times10^9\,\mbox{GeV}$. Additionally, the model requires a vanishing absolute neutrino mass scale $m_1\simeq0$.

Resonant mono Higgs at the LHC

In recent years, the production of a SM particle with large missing transverse momentum, dubbed mono-X searches, have gained increasing attention. After the discovery of the Higgs boson in 2012, the run-II of the LHC will now scrutinise its properties, looking for BSM physics. In particular, one could search for mono-Higgs signals, that are typically studied in models addressing dark matter. However, this signal can appear also in models addressing the neutrino masses, if additional heavier neutrinos with masses at the electroweak scale are present. The latter will couple to the SM neutrinos and the Higgs boson, yielding a type of mono-Higgs signal not considered for dark matter: the resonant production of a Higgs boson and missing energy. In this paper, we address the LHC exclusion power of the latter with dedicated detector simulations, and reinterpret it in a benchmark scenario for neutrino mass generation.

On the stability of the electroweak vacuum in the presence of low-scale seesaw models

The scale of neutrino masses and the Planck scale are separated by more than twenty-seven order of magnitudes. However, they can be linked by imposing the stability of the electroweak (EW) vacuum. The crucial ingredient is provided by the generation of neutrino masses via a seesaw mechanism triggered by Yukawa interactions between the standard model (SM) Higgs and lepton doublets and additional heavy right-handed neutrinos. These neutrinos participate to the renormalization group (RG) running of the dimensionless SM couplings, affecting their high-energy behavior. The Higgs quartic coupling is dragged towards negative values, thus altering the stability of the EW vacuum. In the usual type-I seesaw model, this effect is too small to be a threat since, in order to comply with low-energy neutrino data, one is forced to consider either too small Yukawa couplings or too heavy right-handed neutrinos. In this paper we explore this general idea in the context of low-scale seesaw models. These models are characterized by sizable Yukawa couplings and right-handed neutrinos with mass of the order of the EW scale, thus maximizing their impact on the RG flow. As a general result, we find that Yukawa couplings such that Tr $$ \left({Y}_{{}^v}^{\dagger }{Y}_v\right) $$ ≳ 0.4 are excluded. We discuss the impact of this bound on several observables, with a special focus on the lepton flavor violating process μ → eγ and the neutrino-less double beta decay.

More is different: Reconciling eV sterile neutrinos with cosmological mass bounds

It is generally expected that adding light sterile species would increase the effective number of neutrinos, Neff. In this paper we discuss a scenario that Neff can actually decrease due to the neutrino oscillation effect if sterile neutrinos have self-interactions. We specifically focus on the eV mass range, as suggested by the neutrino anomalies. With large self-interactions, sterile neutrinos are not fully thermalized in the early Universe because of the suppressed effective mixing angle or matter effect. As the Universe cools down, flavor equilibrium between active and sterile species can be reached after big bang nucleosynthesis (BBN) epoch, but leading to a decrease of Neff. In such a scenario, we also show that the conflict with cosmological mass bounds on the additional sterile neutrinos can be relaxed further when more light species are introduced. To be consistent with the latest Planck results, at least 3 sterile species are needed.

Calculation of oscillation probabilities of atmospheric neutrinos using nuCraft

NuCraft (nucraft.hepforge.org) is an open-source Python project that calculates neutrino oscillation probabilities for neutrinos from cosmic-ray interactions in the atmosphere for their propagation through Earth. The solution is obtained by numerically solving the Schrödinger equation. The code supports arbitrary numbers of neutrino flavors including additional sterile neutrinos, CP violation, arbitrary mass hierarchies, matter effects with a configurable continuous Earth model, and takes into account the production height distribution of neutrinos in the Earth’s atmosphere. Program summaryProgram title: nuCraftCatalogue identifier: AEXK_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEXK_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Revised BSD LicenseNo. of lines in distributed program, including test data, etc.: 3017No. of bytes in distributed program, including test data, etc.: 467122Distribution format: tar.gzProgramming language: Python.Computer: IA32/x86-64 compatible.Operating system: All that are supported by SciPy, e.g., Linux, Windows, OS X.RAM: 134217728 bytesClassification: 1.1, 11.1, 11.6.External routines: NumPy (1.5.1 or newer), SciPy (0.8.0 or newer)Nature of problem:Calculation of oscillation probabilities of neutrinos that originate in cosmic-ray interactions in the Earth’s atmosphere and propagate through the Earth, for realistic Earth and atmospheric models and multiple flavors (optionally including sterile neutrinos and CP violation).Solution method:Direct solution of the Schrödinger equation for n flavors including matter effects, with sampling of the atmosphere.Restrictions:Energy loss and absorption of neutrinos inside the Earth is not modeled; they have to be handled independently.Unusual features:Completely configurable oscillation parameters (including optional sterile flavors), configurable and realistic Earth model including atmosphere.Running time:Roughly 100 neutrinos per second and CPU core (depends on energy and oscillation parameters).

Non-Abelian dark matter and dark radiation

We propose a new class of dark matter models with unusual phenomenology. What is ordinary about our models is that dark matter particles are WIMPs, they are weakly coupled to the Standard Model and have weak scale masses. What is unusual is that they come in multiplets of a new "dark" non-Abelian gauge group with milli-weak coupling. The massless dark gluons of this dark gauge group contribute to the energy density of the universe as a form of weakly self-interacting dark radiation. In this paper we explore the consequences of having i.) dark matter in multiplets ii.) self-interacting dark radiation and iii.) dark matter which is weakly coupled to dark radiation. We find that i.) dark matter cross sections are modified by multiplicity factors which have significant consequences for collider searches and indirect detection, ii.) dark gluons have thermal abundances which affect the CMB as dark radiation. Unlike additional massless neutrino species the dark gluons are interacting and have vanishing viscosity and iii.) the coupling of dark radiation to dark matter represents a new mechanism for damping the large scale structure power spectrum. A combination of additional radiation and slightly damped structure is interesting because it can remove tensions between global $\Lambda$CDM fits from the CMB and direct measurements of the Hubble expansion rate ($H_0$) and large scale structure ($\sigma_8$).

Constraints on a seesaw model leading to quasidegenerate neutrinos and signatures at the LHC

We consider a variant of TeV scale seesaw models in which three additional heavy right handed neutrinos are added to the standard model to generate the quasi-degenerate light neutrinos. This model is theoretically interesting since it can be fully rebuilt from the experimental data of neutrino oscillations except for an unknown factor in the Dirac Yukawa coupling. We study the constrains on this coupling coming from meta-stability of electro-weak vacuum. Even stronger bound comes from the lepton flavor violating decays on this model, especially in a heavy neutrino mass scenario which is within the collider reach. Bestowed with these constrained parameters, we explore the production and discovery potential coming from these heavy neutrinos at the $14$~TeV run of Large Hadron Collider. Signatures with tri-lepton final state together with backgrounds are considered in a realistic simulation.