arXiv subjects

Werner Rodejohann

Publications and source records attributed to Werner Rodejohann.

At least 19 recordsLinked to original sources

arXiv2023

Tritium beta decay with modified neutrino dispersion relations: KATRIN in the dark sea

We explore beta decays in a dark background field, which could be formed by dark matter, dark energy or a fifth force potential. In such scenarios, the neutrino's dispersion relation will be modified by its collective interaction with the dark field, which can have interesting consequences in experiments using tritium beta decays to determine the absolute neutrino mass. Among the most general interaction forms, the (pseudo)scalar and (axial-)vector ones are found to have interesting effects on the spectrum of beta decays. In particular, the vector and axial-vector potentials can induce distinct signatures by shifting the overall electron energy scale, possibly beyond the usually defined endpoint. The scalar and pseudoscalar potentials are able to mimic a neutrino mass beyond the cosmological bounds. We have placed stringent constraints on the dark potentials based on the available experimental data of KATRIN. The sensitivity of future KATRIN runs is also discussed.

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arXiv2023

Probing New Physics at Future Tau Neutrino Telescopes

We systematically investigate new physics scenarios that can modify the interactions between neutrinos and matter at upcoming tau neutrino telescopes, which will test neutrino-proton collisions with energies $ \gtrsim 45~{\rm TeV}$, and can provide unique insights to the elusive tau neutrino. At such high energy scales, the impact of parton distribution functions of second and third generations of quarks (usually suppressed) can be comparable to the contribution of first generation with small momentum fraction, hence making tau neutrino telescopes an excellent facility to probe new physics associated with second and third families. Among an inclusive set of particle physics models, we identify new physics scenarios at tree level that can give competitive contributions to the neutrino cross sections while staying within laboratory constraints: charged/neutral Higgs and leptoquarks. Our analysis is close to the actual experimental configurations of the telescopes, and we perform a $χ^2$-analysis on the energy and angular distributions of the tau events. By numerically solving the propagation equations of neutrino and tau fluxes in matter, we obtain the sensitivities of representative upcoming tau neutrino telescopes, GRAND, POEMMA and Trinity, to the charged Higgs and leptoquark models. While each of the experiments can achieve a sensitivity better than the current collider reaches for certain models, their combination is remarkably complementary in probing the new physics. In particular, the new physics will affect the energy and angular distributions in different ways at those telescopes.

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arXiv2022

Search for Leptophilic Dark Matter at the LHeC

The Large Hadron electron Collider (LHeC) has been designed to push the field of deep inelastic scattering to the high energy and intensity frontier using an intense electron beam with a proton beam from the High Luminosity-Large Hadron Collider. However, LHeC is also a great laboratory for new physics. In this work, we propose a search for dark matter that couples with leptons. This may yield $ej$+ missing energy and $μj$ + missing energy signals that can be potentially observed through simple missing-energy cuts that suppress the Standard Model background. Considering direct dark matter detection and LHC constraints, we show that LHeC can indeed discover a weak scale dark matter fermion for masses up to 350 GeV, which reproduces the correct relic density, and has interesting implications for lepton flavor violation.

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arXiv2022

Searching for new physics from SMEFT and leptoquarks at the P2 experiment

The P2 experiment aims at high-precision measurements of the parity-violating asymmetry in elastic electron-proton and electron-$^{12}$C scatterings with longitudinally polarized electrons. We discuss here the sensitivity of P2 to leptoquarks, which within the P2 energy range can be described in the language of Standard Model Effective Field Theory (SMEFT). We give the expected P2 limits on the SMEFT operators and on the leptoquark parameters, which will test energy scales up to 15 TeV. In many cases those limits exceed current constraints from LHC and atomic parity violation (APV) experiments. We also demonstrate that degeneracies of different SMEFT operators can partially be resolved by use of APV experiments and different targets (protons and $^{12}$C) at P2. Moreover, we show that P2 could confirm or resolve potential tensions between the theoretical and experimental determinations of the weak charge of $^{133}$Cs.

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arXiv2022

Microscopic and Macroscopic Effects in the Decoherence of Neutrino Oscillations

We present a generic structure (the layer structure) for decoherence effects in neutrino oscillations, which includes decoherence from quantum mechanical and classical uncertainties. The calculation is done by combining the concept of open quantum system and quantum field theory, forming a structure composed of phase spaces from microscopic to macroscopic level. Having information loss at different levels, quantum mechanical uncertainties parameterize decoherence by an intrinsic mass eigenstate separation effect, while decoherence for classical uncertainties is typically dominated by a statistical averaging effect. With the help of the layer structure, we classify the former as state decoherence (SD) and the latter as phase decoherence (PD), then further conclude that both SD and PD result from phase wash-out effects of different phase structures on different layers. Such effects admit for simple numerical calculations of decoherence for a given width and shape of uncertainties. While our structure is generic, so are the uncertainties, nonetheless, a few notable ones are: the wavepacket size of the external particles, the effective interaction volume at production and detection, the energy reconstruction model and the neutrino production profile. Furthermore, we estimate the experimental sensitivities for SD and PD parameterized by the uncertainty parameters, for reactor neutrinos and decay-at-rest neutrinos, using a traditional rate measuring method and a novel phase measuring method.

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arXiv2022

Probing Heavy Sterile Neutrinos at Ultrahigh Energy Neutrino Telescopes via the Dipole Portal

The question of how heavy a sterile neutrino can be probed in experiments leads us to investigate the Primakoff production of heavy sterile neutrinos up to PeV masses from ultrahigh-energy neutrinos via the magnetic dipole portal. Despite the suppression from the small magnetic moment, the transition is significantly enhanced by tiny $t$-channel momentum transfers, similar to the resonant production of pions and axions in an external electromagnetic field. Based on the current IceCube measurement of astrophysical neutrinos up to PeV energies, strong constraints can already be derived on the transition magnetic moments of sterile neutrinos up to TeV masses. Moreover, we investigate the sensitivity of future tau neutrino telescopes, which are designed for EeV cosmogenic neutrino detection. We find that sterile neutrino masses as large as $30~{\rm TeV}$ can be probed at tau neutrino telescopes such as GRAND, POEMMA, and Trinity.

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arXiv2021

Prospects for Finding Sterile Neutrino Dark Matter at KATRIN

We discuss under what circumstances a signal in upcoming laboratory searches for keV-scale sterile neutrinos would be compatible with those particles being a sizable part or all of dark matter. In the parameter space that will be experimentally accessible by KATRIN/TRISTAN, strong X-ray limits need to be relaxed and dark matter overproduction needs to be avoided. We discuss postponing the dark matter production to lower temperatures, a reduced sterile neutrino contribution to dark matter, and a reduction of the branching ratio in photons and active neutrinos through cancellation with a new physics diagram. Both the Dodelson-Widrow and the Shi-Fuller mechanisms for sterile neutrino dark matter production are considered. As a final exotic example, potential consequences of CPT violation are discussed.

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arXiv2021

Sterile neutrino dark matter production in presence of non-standard neutrino self-interactions: an EFT approach

Sterile neutrinos with keV-scale masses are popular candidates for warm dark matter. In the most straightforward case they are produced via oscillations with active neutrinos. We introduce effective self-interactions of active neutrinos and investigate the effect on the parameter space of sterile neutrino mass and mixing. Our focus is on mixing with electron neutrinos, which is subject to constraints from several upcoming or running experiments like TRISTAN, ECHo, BeEST and HUNTER. Depending on the size of the self-interaction, the parameter space moves closer to, or further away from, the one testable by those future experiments. In particular, we show that phase 3 of the HUNTER experiment would test a larger amount of parameter space in the presence of self-interactions than without them. We also investigate the effect of the self-interactions on the free-streaming length of the sterile neutrino dark matter, which is important for structure formation observables.

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arXiv2021

Probing the $R_{K^{(*)}}$ Anomaly at a Muon Collider

The LHCb measurements of the $μ/ e$ ratio in $B \to K \ell \ell$ decays $(R_{K^{}})$ indicate a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the $R_{K^{(*)}}$ ratio. Possible explanations of these $B$-physics anomalies include heavy $Z'$ bosons or scalar and vector leptoquarks mediating $b \to s μ^+ μ^- $. We note that a muon collider can directly measure this process via $μ^+ μ^- \to b \bar s$ and can shed light on the lepton non-universality scenario. Investigating currently discussed center-of-mass energies $\sqrt{s} = 3$, 6 and 10 TeV, we show that the parameter space of $Z'$ and leptoquark solutions to the $R_{K^{(*)}}$ anomalies can be mostly covered. Effective operators explaining the anomalies can be probed with the muon collider setup $\sqrt{s} = 6~{\rm TeV}$ and integrated luminosity $L = 4~{\rm ab^{-1}}$.

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arXiv2021

Status and Perspectives of Neutrino Physics

This review demonstrates the unique role of the neutrino by discussing in detail the physics of and with neutrinos. We deal with neutrino sources, neutrino oscillations, absolute masses, interactions, the possible existence of sterile neutrinos, and theoretical implications. In addition, synergies of neutrino physics with other research fields are found, and requirements to continue successful neutrino physics in the future, in terms of technological developments and adequate infrastructures, are stressed.

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arXiv2021

Laboratory limits on the annihilation or decay of dark matter particles

Constraints on the indirect detection of dark matter are usually obtained from observations of astrophysical objects -- the Galactic Center, dwarf galaxies, M31, etc. Here we propose instead to look for the annihilation or decay of dark matter particles taking place inside detectors searching \emph{directly} for dark matter or in large neutrino experiments. We show that the data from XENON1T and Borexino set limits on the annihilation and decay rate of dark matter particles with masses in the keV to few MeV range. All relevant final states are considered: annihilation into $γγ$ and $e^-e^+$, and decays into $γγ$, $γν$ and $e^-e^+$. The expected sensitivities in XENONnT, DARWIN, JUNO and THEIA are also computed. Though weaker than current astrophysical bounds, the laboratory limits (and projections) obtained are free from the usual astrophysical uncertainties associated with $J$-factors and unknown backgrounds, and may thus offer a complementary probe of the dark matter properties. We point out that current and future (astro)particle physics detectors might also be used to set analogous limits for different decays and dark matter masses above a few MeV.

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arXiv2021

Leptogenesis and low-energy CP violation in a type-II-dominated left-right seesaw model

We consider leptogenesis in a left-right-symmetric seesaw scenario in which neutrino mass generation and leptogenesis are dominated by the type-II seesaw term. Motivated by grand unification, we assume that the neutrino Dirac mass matrix is dominated by a single entry of the order of the top-quark mass, which leaves the low-energy phases of the lepton mixing matrix as the only sources of CP violation. Working in a regime where the triplet scalar predominantly decays into leptons, this results in a predictive scenario based on a minimal number of parameters. We perform a detailed analysis of the flavored Boltzmann equations within a revised density matrix framework and demonstrate that the observed baryon asymmetry can be successfully generated in this simple model. We point out that the significance of flavor effects is limited, and we discuss the implications for low-energy observables such as the Dirac CP phase and neutrinoless double beta decay.

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arXiv2021

Searching for $Z'$ bosons at the P2 experiment

The P2 experiment aims at high-precision measurements of the parity-violating asymmetry in elastic electron-proton and electron-$^{12}$C scatterings with longitudinally polarized electrons. We discuss here the sensitivity of P2 to new physics mediated by an additional neutral gauge boson $Z'$ of a new $U(1)'$ gauge symmetry. If the charge assignment of the $U(1)'$ is chiral, i.e., left- and right-handed fermions have different charges under $U(1)'$, additional parity-violation is induced directly. On the other hand, if the $U(1)'$ has a non-chiral charge assignment, additional parity-violation can be induced via mass or kinetic $Z$-$Z'$ mixing. By comparing the P2 sensitivity to existing constraints, we show that in both cases P2 has discovery potential over a wide range of $Z'$ mass. In particular, for chiral models, the P2 experiment can probe gauge couplings at the order of $10^{-5}$ when the $Z'$ boson is light, and heavy $Z'$ bosons up to 79 (90) TeV in the proton ($^{12}$C) mode. For non-chiral models with mass mixing, the P2 experiment is sensitive to mass mixing angles smaller than roughly $10^{-4}$, depending on model details and gauge coupling magnitude.

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arXiv2021

Seesaw neutrino dark matter by freeze-out

We investigate whether right-handed neutrinos can play the role of the dark matter of the Universe and be generated by the freeze-out production mechanism. In the standard picture, the requirement of a long lifetime of the right-handed neutrinos implies a small neutrino Yukawa coupling. As a consequence, they never reach thermal equilibrium, thus prohibiting production by freeze-out. We note that this limitation is alleviated if the neutrino Yukawa coupling is large enough in the early Universe to thermalize the sterile neutrinos, and then becomes tiny at a certain moment, which makes them drop out of equilibrium. As a concrete example realization of this framework, we consider a Froggatt-Nielsen model supplemented by an additional scalar field which obeys a global symmetry (not the flavour symmetry). Initially, the vacuum expectation value of the flavon is such, that the effective neutrino Yukawa coupling is large and unsuppressed, keeping them in thermal equilibrium. At some point the new scalar also gets a vacuum expectation value that breaks the symmetry. This may occur in such a way that the vev of the flavon is shifted to a new (smaller) value. In that case, the Yukawa coupling is reduced such that the sterile neutrinos are rendered stable on cosmological time scales. We show that this mechanism works for a wide range of sterile neutrino masses.

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arXiv2021

CP-Violating and Charged Current Neutrino Non-standard Interactions in CE$ν$NS

Neutrino non-standard interactions (NSI) can be constrained using coherent elastic neutrino-nucleus scattering. We discuss here two aspects in this respect, namely the effects of (i) charged current NSI in neutrino production and (ii) CP-violating phases associated with neutral current NSI in neutrino detection. Effects of CP-phases require the simultaneous presence of two different flavor-changing neutral current NSI parameters. Applying these two scenarios to the COHERENT measurement, we derive limits on charged current NSI and find that more data is required to compete with the existing limits. Regarding CP-phases, we show how the limits on the NSI parameters depend dramatically on the values of the phases. Accidentally, the same parameters influencing coherent scattering also show up in neutrino oscillation experiments. We find that COHERENT provides complementary constraints on the set of NSI parameters that can explain the discrepancy in the best-fit value of the standard CP-phase obtained by T2K and NO$ν$A, while the significance with which the LMA-Dark solution is ruled out can be weakened by the presence of additional NSI parameters introduced here.

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arXiv2021

Dirac neutrinos and $N_{\rm eff}$ II: the freeze-in case

We discuss Dirac neutrinos whose right-handed component $ν_R$ has new interactions that may lead to a measurable contribution to the effective number of relativistic neutrino species $N_{\rm eff}$. We aim at a model-independent and comprehensive study on a variety of possibilities. Processes for $ν_R$-genesis from decay or scattering of thermal species, with spin-0, spin-1/2, or spin-1 initial or final states are all covered. We calculate numerically and analytically the contribution of $ν_R$ to $N_{\rm eff}$ primarily in the freeze-in regime, since the freeze-out regime has been studied before. While our approximate analytical results apply only to freeze-in, our numerical calculations work for freeze-out as well, including the transition between the two regimes. Using current and future constraints on $N_{\rm eff}$, we obtain limits and sensitivities of CMB experiments on masses and couplings of the new interactions. As a by-product, we obtain the contribution of Higgs-neutrino interactions, $ΔN_{\rm eff}^{\rm SM} \approx 7.5\times10^{-12}$, assuming the neutrino mass is 0.1 eV and generated by the standard Higgs mechanism.

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arXiv2021

Solving the Hubble tension without spoiling Big Bang Nucleosynthesis

The Hubble parameter inferred from cosmic microwave background observations is consistently lower than that from local measurements, which could hint towards new physics. Solutions to the Hubble tension typically require a sizable amount of extra radiation $ΔN^{}_{\rm eff}$ during recombination. However, the amount of $ΔN^{}_{\rm eff}$ in the early Universe is unavoidably constrained by Big Bang Nucleosynthesis (BBN), which causes problems for such solutions. We present a possibility to evade this problem by introducing neutrino self-interactions via a simple Majoron-like coupling. The scalar is slightly heavier than $1~{\rm MeV}$ and allowed to be fully thermalized throughout the BBN era. The rise of neutrino temperature due to the entropy transfer via $ϕ\to ν\overlineν$ reactions compensates the effect of a large $ΔN^{}_{\rm eff}$ on BBN. Values of $ΔN^{}_{\rm eff}$ as large as $0.7$ are in this case compatible with BBN. We perform a fit to the parameter space of the model.

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arXiv2021

Gauged $L^{}_μ{-}L^{}_τ$ at a muon collider

We investigate the sensitivity of the projected TeV muon collider to the gauged $L^{}_μ$-$L^{}_τ$ model. Two processes are considered: $Z'$-mediated two-body scatterings $μ^+ μ^- \to \ell^+ \ell^-$ with $\ell = μ$ or $τ$, and scattering with initial state photon emission, $μ^+ μ^- \to γZ',~Z' \to \ell \overline{\ell}$, where $\ell$ can be $μ$, $τ$ or $ν_{μ/τ}$. We quantitatively study the sensitivities of these two processes by taking into account possible signals and relevant backgrounds in a muon collider experiment with a center-of-mass energy $\sqrt{s} = 3~{\rm TeV}$ and a luminosity $L=1~{\rm ab^{-1}}$. For two-body scattering one can exclude $Z'$ masses $M^{}_{Z'} \lesssim 100~{\rm TeV}$ with $\mathcal{O}(1)$ gauge couplings. When $M^{}_{Z'} \lesssim 1~{\rm TeV} <\sqrt{s}$, one can exclude $g' \gtrsim 2\times 10^{-2}$. The process with photon emission is more powerful than the two-body scattering if $M^{}_{Z'} < \sqrt{s}$. For instance, a sensitivity of $g' \simeq 4 \times 10^{-3}$ can be achieved at $M^{}_{Z'} = 1~{\rm TeV}$. The parameter spaces favored by the $(g-2)^{}_μ$ and $B$ anomalies with $M^{}_{Z'} > 100~{\rm GeV}$ are entirely covered by a muon collider.

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