arXiv subjects

Manfred Lindner

Publications and source records attributed to Manfred Lindner.

At least 73 records · Page 4Linked to original sources

arXiv2018

Coherent scattering and macroscopic coherence: Implications for neutrino, dark matter and axion detection

We study the question of whether coherent neutrino scattering can occur on macroscopic scales, leading to a significant increase of the detection cross section. We concentrate on radiative neutrino scattering on atomic electrons (or on free electrons in a conductor). Such processes can be coherent provided that the net electron recoil momentum, i.e. the momentum transfer from the neutrino minus the momentum of the emitted photon, is sufficiently small. The radiative processes is an attractive possibility as the energy of the emitted photons can be as large as the momentum transfer to the electron system and therefore the problem of detecting extremely low energy recoils can be avoided. The requirement of macroscopic coherence severely constrains the phase space available for the scattered particle and the emitted photon. We show that in the case of the scattering mediated by the usual weak neutral current and charged current interactions this leads to a strong suppression of the elementary cross sections and therefore the requirement of macroscopic coherence results in a reduction rather than an increase of the total detection cross section. However, for the $νe$ scattering mediated by neutrino magnetic or electric dipole moments coherence effects can actually increase the detection rates. Effects of macroscopic coherence can also allow detection of neutrinos in 100 eV -- a few keV energy range, which is currently not accessible to the experiment. A similar coherent enhancement mechanism can work for relativistic particles in the dark sector, but not for the conventionally considered non-relativistic dark matter.

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arXiv2018

Supernova Neutrino Neutrino Astronomy

Modern neutrino facilities will be able to detect a large number of neutrinos from the next Galactic supernova. We investigate the viability of the triangulation method to locate a core-collapse supernova by employing the neutrino arrival time differences at various detectors. We perform detailed numerical fits in order to determine the uncertainties of these time differences for the cases when the core collapses into a neutron star or a black hole. We provide a global picture by combining all the relevant current and future neutrino detectors. Our findings indicate that in the scenario of a neutron star formation, supernova can be located with precision of 1.5 and 3.5 degrees in declination and right ascension, respectively. For the black hole scenario, sub-degree precision can be reached.

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arXiv2018

Neutrino Parameters from Reactor and Accelerator Neutrino Experiments

We revisit correlations of neutrino oscillation parameters in reactor and long-baseline neutrino oscillation experiments. A framework based on an effective value of $θ_{13}$ is presented, which can easily reproduce experimental results. It also clarifies why current and future long-baseline experiments will have less precision on values around $δ_{CP} = \pm π/2$ than on values around $δ_{CP} = 0$. Optimization potential for the determination of the theoretically very interesting values around $δ_{CP} = -π/2$ is also pointed out, which would require that future runs of accelerator experiments are not equally shared $1:1$ in neutrino and antineutrino modes, but rather $2:1$. Recent hints on the CP phase and the mass ordering are then considered from the point of view that different reactor and long-baseline neutrino experiments provide currently different best-fit values of $θ_{13}$ and $θ_{23}$. We point out that the significance of the hints changes for the different available best-fit values.

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arXiv2018

MeV Dark Matter Complementarity and the Dark Photon Portal

We discuss the phenomenology of an MeV-scale Dirac fermion coupled to the Standard Model through a dark photon with kinetic mixing with the electromagnetic field. We compute the dark matter relic density and explore the interplay of direct detection and accelerator searches for dark photons. We show that precise measurements of the temperature and polarization power spectra of the Cosmic Microwave Background Radiation lead to stringent constraints, leaving a small window for the thermal production of this MeV dark matter candidate. The forthcoming MeV gamma-ray telescope e-ASTROGAM will offer important and complementary opportunities to discover dark matter particles with masses below 10 MeV. Lastly, we discuss how a late-time inflation episode and freeze-in production could conspire to yield the correct relic density while being consistent with existing and future constraints.

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arXiv2018

Pseudoscalar Mediators: A WIMP model at the Neutrino Floor

Due to its highly suppressed cross section (fermionic) dark matter interacting with the Standard Model via pseudoscalar mediators is expected to be essentially unobservable in direct detection experiments. We consider both a simplified model and a more realistic model based on an extended two Higgs doublet model and compute the leading one-loop contribution to the effective dark matter- nucleon interaction. This higher order correction dominates the scattering rate completely and can naturally, i.e. for couplings of order one, lead to a direct detection cross section in the vicinity of the neutrino floor. Taking the observed relic density and constraints from low-energy observables into account we analyze the direct detection prospects in detail and find regions of parameter space that are within reach of upcoming direct detection experiments such as XENONnT, LZ, and DARWIN.

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arXiv2018

Neutrino-Electron Scattering: General Constraints on Z' and Dark Photon Models

We study the framework of $U(1)_X$ models with kinetic mixing and/or mass mixing terms. We give general and exact analytic formulas and derive limits on a variety of $U(1)_X$ models that induce new physics contributions to neutrino-electron scattering, taking into account interference between the new physics and Standard Model contributions. Data from TEXONO, CHARM-II and GEMMA are analyzed and shown to be complementary to each other to provide the most restrictive bounds on masses of the new vector bosons. In particular, we demonstrate the validity of our results to dark photon-like as well as light $Z^\prime$ models.

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arXiv2018

Probing neutrino coupling to a light scalar with coherent neutrino scattering

Large neutrino event numbers in future experiments measuring coherent elastic neutrino nucleus scattering allow precision measurements of standard and new physics. We analyze the current and prospective limits of a light scalar particle coupling to neutrinos and quarks, using COHERENT and CONUS as examples. Both lepton number conserving and violating interactions are considered. It is shown that current (future) experiments can probe for scalar masses of a few MeV couplings down to the level of $10^{-4}$ $(10^{-6})$. Scalars with masses around the neutrino energy allow to determine their mass via a characteristic spectrum shape distortion. Our present and future limits are compared with constraints from supernova evolution, Big Bang nucleosynthesis and neutrinoless double beta decay. We also outline UV-complete underlying models that include a light scalar with coupling to quarks for both lepton number violating and conserving coupling to neutrinos.

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arXiv2017

A Call for New Physics : The Muon Anomalous Magnetic Moment and Lepton Flavor Violation

We review how the muon anomalous magnetic moment ($g-2$) and the quest for lepton flavor violation are intimately correlated. Indeed the decay $μ\to e γ$ is induced by the same amplitude for different choices of in- and outgoing leptons. In this work, we try to address some intriguing questions such as: Which hierarchy in the charged lepton sector one should have in order to reconcile possible signals coming simultaneously from $g-2$ and lepton flavor violation? What can we learn if the $g-2$ anomaly is confirmed by the upcoming flagship experiments at FERMILAB and J-PARC, and no signal is seen in the decay $μ\rightarrow eγ$ in the foreseeable future? On the other hand, if the $μ\rightarrow eγ$ decay is seen in the upcoming years, do we need to necessarily observe a signal also in $g-2$?. In this attempt, we generally study the correlation between these observables in a detailed analysis of simplified models. We derive master integrals and fully analytical and exact expressions for both phenomena, and adress other flavor violating signals. We investigate under which conditions the observations can be made compatible and discuss their implications. Lastly, we discuss in this context several extensions of the SM, such as the Minimal Supersymmetric Standard Model, Left-Right symmetric model, $B-L$ model, scotogenic model, two Higgs doublet model, Zee-Babu model, 331 model, and $L_μ-L_τ$, dark photon, seesaw models type~I, II and III, and also address the interplay with $μ\to eee$ decay and $μ-e$ conversion.

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arXiv2017

Collective neutrino oscillations and neutrino wave packets

Effects of decoherence by wave packet separation on collective neutrino oscillations in dense neutrino gases are considered. We estimate the length of the wave packets of neutrinos produced in core collapse supernovae and the expected neutrino coherence length, and then proceed to consider the decoherence effects within the density matrix formalism of neutrino flavour transitions. First, we demonstrate that for neutrino oscillations in vacuum the decoherence effects are described by a damping term in the equation of motion of the density matrix of a neutrino as a whole (as contrasted to that of the fixed-momentum components of the neutrino density matrix). Next, we consider neutrino oscillations in ordinary matter and dense neutrino backgrounds, both in the adiabatic and non-adiabatic regimes. In the latter case we study two specific models of adiabaticity violation -- one with short-term and another with extended non-adiabaticity. It is demonstrated that, while in the adiabatic case a damping term is present in the equation of motion of the neutrino density matrix (just like in the vacuum oscillation case), no such term in general appears in the non-adiabatic regime.

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arXiv2017

Emerging Internal Symmetries from Effective Spacetimes

Can global internal and spacetime symmetries be connected without supersymmetry? To answer this question, we investigate Minkowski spacetimes with d space-like extra dimensions and point out under which general conditions external symmetries induce internal symmetries in the effective 4-dimensional theories. We further discuss in this context how internal degrees of freedom and spacetime symmetries can mix without supersymmetry in agreement with the Coleman-Mandula theorem. We present some specific examples which rely on a direct product structure of spacetime such that orthogonal extra dimensions can have symmetries which mix with global internal symmetries. This mechanism opens up new opportunities to understand global symmetries in particle physics.

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arXiv2017

Gravitational Waves as a New Probe of Bose-Einstein Condensate Dark Matter

There exists a class of ultralight Dark Matter (DM) models which could form a Bose-Einstein condensate (BEC) in the early universe and behave as a single coherent wave instead of individual particles in galaxies. We show that a generic BEC DM halo intervening along the line of sight of a gravitational wave (GW) signal could induce an observable change in the speed of GW, with the effective refractive index depending only on the mass and self-interaction of the constituent DM particles and the GW frequency. Hence, we propose to use the deviation in the speed of GW as a new probe of the BEC DM parameter space. With a multi-messenger approach to GW astronomy and/or with extended sensitivity to lower GW frequencies, the entire BEC DM parameter space can be effectively probed by our new method in the near future.

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arXiv2017

Minimal conformal extensions of the Higgs sector

In this work we find the minimal extension of the Standard Model's Higgs sector which can lead to a light Higgs boson via radiative symmetry breaking and is consistent with the phenomenological requirements for a low-energy realization of a conformal theory. The model which turns out to be stable under renormalization group translations is an extension of the Standard Model by two scalar fields, one of which acquires a finite vacuum expectation value and therefore mixes into the physical Higgs. We find that the minimal model predicts a sizable amount of mixing which makes it testable at a collider. In addition to the physical Higgs, the theory's scalar spectrum contains one light and one heavy boson. The heavy scalar's properties render it a potential dark matter candidate.

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arXiv2017

The Dark Sequential Z' Portal: Collider and Direct Detection Experiments

We revisit the status of a Majorana fermion as a dark matter candidate when a sequential Z' gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and mono-jet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities.

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arXiv2017

Revisiting Large Neutrino Magnetic Moments

Current experimental sensitivity on neutrino magnetic moments is many orders of magnitude above the Standard Model prediction. A potential measurement of next-generation experiments would therefore strongly request new physics beyond the Standard Model. However, large neutrino magnetic moments generically tend to induce large corrections to the neutrino masses and lead to fine-tuning. We show that in a model where neutrino masses are proportional to neutrino magnetic moments. We revisit, discuss and propose mechanisms that still provide theoretical consistent explanations for a potential measurement of large neutrino magnetic moments. We find only two viable mechanisms to realize large transition magnetic moments for Majorana neutrinos only.

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arXiv2017

Neutrino Masses and Absence of Flavor Changing Interactions in the 2HDM from Gauge Principles

We propose several Two Higgs Doublet Models with the addition of an Abelian gauge group which free the usual framework from flavor changing neutral interactions and explain neutrino masses through the seesaw mechanism. We discuss the kinetic and mass-mixing gripping phenomenology which encompass several constraints coming from atomic parity violation, the muon anomalous magnetic moment, rare meson decays, Higgs physics, LEP precision data, neutrino-electron scattering, low energy accelerators and LHC probes.

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arXiv2017

GUT Models at Current and Future Hadron Colliders and Implications to Dark Matter Searches

Grand Unified Theories (GUT) offer an elegant and unified description of electromagnetic, weak and strong interactions at high energy scales. A phenomenological and exciting possibility to grasp GUT is to search for TeV scale observables arising from Abelian groups embedded in GUT constructions. That said, we use dilepton data (ee and $μμ$) that has been proven to be a golden channel for a wide variety of new phenomena expected in theories beyond the Standard Model to probe GUT-inspired models. Since heavy dilepton resonances feature high signal selection efficiencies and relatively well-understood backgrounds, stringent and reliable bounds can be placed on the mass of the $Z^{\prime}$ gauge boson arising in such theories. In this work, we obtain 95\% C.L. limits on the $Z^{\prime}$ mass for several GUT-models using current and future proton-proton colliders with $\sqrt{s}= 13~{\rm TeV},\, 33~{\rm TeV},\,{\rm and}\, 100$~TeV, and put them into perspective with dark matter searches in light of the next generation of direct detection experiments.

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arXiv2017

The Waning of the WIMP? A Review of Models, Searches, and Constraints

Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. In light of no conclusive detection signal yet despite an extensive search program that combines, often in a complementary way, direct, indirect, and collider probes, we find it timely to give a broad overview of the WIMP paradigm. In particular, we review here the theoretical foundations of the WIMP paradigm, discuss status and prospects of various detection strategies, and explore future experimental challenges and opportunities.

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arXiv2017

Prospects for three-body Higgs boson decays into extra light scalars

Within models containing a very light scalar particle coupled to the 125 GeV Higgs boson, we present the first detailed study of Higgs decays into three of these light scalars. We determine model-independent conditions which the scalar sector after electroweak symmetry breaking has to satisfy in order for the three-body channel to become relevant. Using a specific model -- the real scalar singlet-extension of the Standard Model (SM) -- we then identify scenarios, where the rates of scalar three-body Higgs decays are comparable to or even exceed those of the well-studied two-body channel. All those scenarios are shown to be compatible with current experimental and theoretical constraints. We finally argue that scalar three-body Higgs decays lead to exciting new collider signatures with six SM fermions in the final state. Calculating the corresponding event rates, we find that e.g. six-muon or six-tau final states may be in reach of dedicated searches at the LHC or ILC experiments.

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