arXiv subjects

Stefan Antusch

Publications and source records attributed to Stefan Antusch.

At least 127 records · Page 7Linked to original sources

arXiv2008

Non-Standard Neutrino Interactions with Matter from Physics Beyond the Standard Model

We investigate how non-standard neutrino interactions (NSIs) with matter can be generated by new physics beyond the Standard Model (SM) and analyse the constraints on the NSIs in these SM extensions. We focus on tree-level realisations of lepton number conserving dimension 6 and 8 operators which do not induce new interactions of four charged fermions (since these are already quite constrained) and discard the possibility of cancellations between diagrams with different messenger particles to circumvent experimental constraints. The cases studied include classes of dimension 8 operators which are often referred to as examples for ways to generate large NSIs with matter. We find that, in the considered scenarios, the NSIs with matter are considerably more constrained than often assumed in phenomenological studies, at least ${\cal O}(10^{-2})$. The constraints on the flavour-conserving NSIs turn out to be even stronger than the ones for operators which also produce interactions of four charged fermions at the same level. Furthermore, we find that in all studied cases the generation of NSIs with matter also gives rise to NSIs at the source and/or detector of a possible future Neutrino Factory.

hep-ph↗

arXiv2008

Perturbative Estimates of Lepton Mixing Angles in Unified Models

Many unified models predict two large neutrino mixing angles, with the charged lepton mixing angles being small and quark-like, and the neutrino masses being hierarchical. Assuming this, we present simple approximate analytic formulae giving the lepton mixing angles in terms of the underlying high energy neutrino mixing angles together with small perturbations due to both charged lepton corrections and renormalisation group (RG) effects, including also the effects of third family canonical normalization (CN). We apply the perturbative formulae to the ubiquitous case of tri-bimaximal neutrino mixing at the unification scale, in order to predict the theoretical corrections to mixing angle predictions and sum rule relations, and give a general discussion of all limiting cases.

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arXiv2008

Phenomenology of Hybrid Scenarios of Neutrino Dark Energy

We study the phenomenology of hybrid scenarios of neutrino dark energy, where in addition to a so-called Mass Varying Neutrino (MaVaN) sector a cosmological constant (from a false vacuum) is driving the accelerated expansion of the universe today. For general power law potentials we calculate the effective equation of state parameter w_{eff}(z) in terms of the neutrino mass scale. Due to the interaction of the dark energy field (acceleron) with the neutrino sector, w_{eff}(z) is predicted to become smaller than -1 for z>0, which could be tested in future cosmological observations. For the considered scenarios, the neutrino mass scale additionally determines which fraction of the dark energy is dynamical, and which originates from the cosmological constant like vacuum energy of the false vacuum. On the other hand, the field value of the acceleron field today as well as the masses of the right-handed neutrinos, which appear in the seesaw-type mechanism for small neutrino masses, are not fixed. This, in principle, allows to realise hybrid scenarios of neutrino dark energy with a high-scale seesaw where the right-handed neutrino masses are close to the GUT scale. We also comment on how MaVaN Hybrid Scenarios with high-scale seesaw might help to resolve stability problems of dark energy models with non-relativistic neutrinos.

astro-ph↗

arXiv2008

Quark and lepton masses at the GUT scale including SUSY threshold corrections

We investigate the effect of supersymmetric (SUSY) threshold corrections on the values of the running quark and charged lepton masses at the GUT scale within the large $\tanβ$ regime of the MSSM. In addition to the typically dominant SUSY QCD contributions for the quarks, we also include the electroweak contributions for quarks and leptons and show that they can have significant effects. We provide the GUT scale ranges of quark and charged lepton Yukawa couplings as well as of the ratios $m_μ/m_s$, $m_e/m_d$, $y_τ/y_b$ and $y_t/y_b$ for three example ranges of SUSY parameters. We discuss how the enlarged ranges due to threshold effects might open up new possibilities for constructing GUT models of fermion masses and mixings.

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arXiv2008

Flavour-Dependent Type II Leptogenesis

We reanalyse leptogenesis via the out-of-equilibrium decay of the lightest right-handed neutrino in type II seesaw scenarios, taking into account flavour-dependent effects. In the type II seesaw mechanism, in addition to the type I seesaw contribution, an additional direct mass term for the light neutrinos is present. We consider type II seesaw scenarios where this additional contribution arises from the vacuum expectation value of a Higgs triplet, and furthermore an effective model-independent approach. We investigate bounds on the flavour-specific decay asymmetries, on the mass of the lightest right-handed neutrino and on the reheat temperature of the early universe, and compare them to the corresponding bounds in the type I seesaw framework. We show that while flavour-dependent thermal type II leptogenesis becomes more efficient for larger mass scale of the light neutrinos, and the bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more constrained. We also argue that in general, flavour-dependent effects cannot be ignored when dealing with leptogenesis in type II seesaw models.

hep-ph↗

arXiv2008

Solving the SUSY Flavour and CP Problems with Non-Abelian Family Symmetry and Supergravity

Can a theory of flavour capable of describing the spectrum of fermion (including neutrino) masses and mixings also contain within it the seeds for a solution of the SUSY flavour and CP problems? We argue that supergravity together with a non-Abelian family symmetry can completely resolve the SUSY flavour and CP problems in a broad class of theories in which family symmetry and CP is spontaneously broken in the flavon sector. We show that a simple superpotential structure can suppresses the F-terms of the flavons and GUT scale Higgs fields and that, if this mechanism is implemented, the resulting flavour and CP violation is suppressed and comfortably within the experimental limits. For illustration, we study a specific model based on SU(3) family symmetry, but similar models based on non-Abelian (continuous or discrete) family symmetry will lead to similar results.

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arXiv2008

Solving the SUSY Flavour and CP Problems with SU(3) Family Symmetry

We show how the SUSY flavour and CP problems can be solved using gauged SU(3) family symmetry previously introduced to describe quark and lepton masses and mixings, in particular neutrino tri-bimaximal mixing via constrained sequential dominance. The Yukawa and soft trilinear and scalar mass squared matrices and kinetic terms are expanded in powers of the flavons used to spontaneously break the SU(3) family symmetry, and the canonically normalized versions of these matrices are constructed. The soft mass matrices are then expressed in the Super-CKM basis, and the leading order mass insertion parameters are calculated, and are shown to satisfy the experimental constraints from flavour changing neutral current processes. Assuming that CP is spontaneously broken by the flavons, the next-to-leading order effects responsible for CP violation are then estimated, and the predictions for electric dipole moments are shown to be an order of magnitude more suppressed than those predicted from the constrained minimal supersymmetric standard model (CMSSM), and may be further suppressed if the high energy trilinear soft parameter is assumed to be relatively small. We also predict that, unlike in the CMSSM, epsilon_K'/epsilon_K may be dominated by the SUSY operator O_8. We also discuss the additional constraints from unification, which can lead to further predictions for flavour changing in our scheme.

hep-ph↗

arXiv2008

Third Family Corrections to Quark and Lepton Mixing in SUSY Models with non-Abelian Family Symmetry

We re-analyse the effect of corrections from canonical normalisation of kinetic terms on the quark and lepton mixing angles. This type of corrections emerges, for example, from effective higher-dimensional Kahler potential operators in the context of locally supersymmetric models of flavour. In contrast to previous studies we find that the necessary procedure of redefining the fields in order to restore canonically normalised kinetic terms, i.e. canonical normalisation, can lead to significant corrections to the fermion mixing angles (as determined from the superpotential). Such potentially large effects are characteristic of flavour models based on non-Abelian family symmetries, where some of the possible Kahler potential (and superpotential) operators, in particular those associated with the third family, are only mildly suppressed. We investigate under which conditions the messenger sector of such flavour models generates such Kahler potential operators for which the canonical normalisation effects are sizeable, and under which conditions these operators may be absent and canonical normalisation effects are small. As explicit examples for potentially relevant CN effects, we will discuss the corrections to the CKM matrix element |V_{cb}| as well as corrections to tri-bimaximal neutrino mixing.

hep-ph↗

arXiv2008

Lepton Flavour Violation in the Constrained MSSM with Constrained Sequential Dominance

We consider charged Lepton Flavour Violation (LFV) in the Constrained Minimal Supersymmetric Standard Model, extended to include the see-saw mechanism with Constrained Sequential Dominance (CSD), where CSD provides a natural see-saw explanation of tri-bimaximal neutrino mixing. When charged lepton corrections to tri-bimaximal neutrino mixing are included, we discover characteristic correlations among the LFV branching ratios, depending on the mass ordering of the right-handed neutrinos, with a pronounced dependence on the leptonic mixing angle $θ_{13}$ (and in some cases also on the Dirac CP phase $δ$).

hep-ph↗

arXiv2007

Third Family Corrections to Tri-bimaximal Lepton Mixing and a New Sum Rule

We investigate the theoretical stability of the predictions of tri-bimaximal neutrino mixing with respect to third family wave-function corrections. Such third family wave-function corrections can arise from either the canonical normalisation of the kinetic terms or renormalisation group running effects. At leading order both sorts of corrections can be subsumed into a single universal parameter. For hierarchical neutrinos, this leads to a new testable lepton mixing sum rule 's = r cos delta + 2/3 a' (where s, r, a describe the deviations of solar, reactor and atmospheric mixing angles from their tri-bimaximal values, and 'delta' is the observable Dirac CP phase) which is stable under all leading order third family wave-function corrections, as well as Cabibbo-like charged lepton mixing effects.

hep-ph↗

arXiv2006

From Unified Theories to Precision Neutrino Experiments

The expected high sensitivities of future neutrino oscillation experiments will allow precision tests of unified theories of flavour. In order to compare GUT scale predictions for neutrino masses, leptonic mixing angles and CP violating phases with experimental results obtained at low energy, their renormalization group running has to be taken into account. We discuss the running in seesaw scenarios, present analytical approximations as well as numerical tools, and compare the size of the running effects with the expected experimental sensitivities.

hep-ph↗

arXiv2006

Sneutrino Hybrid Inflation

We review the scenario of sneutrino hybrid inflation, where one of the singlet sneutrinos, the superpartners of the right-handed neutrinos, plays the role of the inflaton. In a minimal model of sneutrino hybrid inflation, the spectral index is given by $n_s \approx 1 + 2 γ$. With $γ= 0.025 \pm 0.01$ constrained by WMAP, a running spectral index $|d n_s/d \ln k| \ll |γ|$ and a tensor-to-scalar ratio $r \ll γ^2$ are predicted. Small neutrino masses arise from the seesaw mechanism, with heavy masses for the singlet (s)neutrinos generated by the vacuum expectation value of the waterfall field after inflation. The baryon asymmetry of the universe can be explained by non-thermal leptogenesis via sneutrino inflaton decay, with low reheat temperature $T_RH \approx 10^6$ GeV.

hep-ph↗

arXiv2005

Charged Lepton Corrections to Neutrino Mixing Angles and CP Phases Revisited

We re-analyze charged lepton corrections to neutrino mixing angles and CP phases, carefully including CP phases from the charged lepton sector. We present simple analytical formulae for including the charged lepton corrections and derive compact new results for small neutrino and charged lepton mixings $θ^ν_{13}$ and $θ^{e}_{13}$. We find a generic relation $θ_{12} + \frac{1}{\sqrt{2}} θ^{e}_{12} \cos(δ- π) \approx θ^ν_{12}$, which relates the prediction from the neutrino sector $θ^ν_{12}$ to the charged lepton mixing $θ^{e}_{12}$ and to the MNS neutrino oscillation phase $δ$. We apply our formula to the examples of bimaximal or tri-bimaximal neutrino mixing. One implication is that the so-called quark-lepton complementarity relation $θ_{12} + θ_C = 45^\circ$ can only hold for $δ= π$ and it gets modified in the presence of leptonic CP violation. On the other hand, the lepton mixing $θ_{13}$ generated from the charged lepton correction $θ^{e}_{12}$ is independent of CP phases and given by $θ_{13} = \frac{1}{\sqrt{2}} θ^{e}_{12}$. Combining these results leads to a model-independent sum rule: $θ_{12} + θ_{13} \cos(δ- π) \approx θ^ν_{12}$ where $θ^ν_{12} = (35.26^\circ) 45^\circ$ in the case of (tri-)bimaximal neutrino mixing, for example.

hep-ph↗

arXiv2005

Leptogenesis in Unified Theories with Type II See-Saw

In some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced, relaxing the lower bound on the mass of the lightest right-handed neutrino from thermal leptogenesis. For instance in classes of unified theories where the lightest right-handed neutrino dominates the type I see-saw contribution, we find that thermal leptogenesis becomes possible if the neutrino mass scale is larger than about 0.15 eV, making this scenario testable by neutrinoless double beta decay experiments in the near future.

hep-ph↗

arXiv2005

Quark-Lepton Complementarity in Unified Theories

As pointed out by many authors, recent observations are consistent with an intriguing relation between the Cabibbo angle $θ_C$ and the solar neutrino mixing angle $θ_{12}$, namely $θ_{12} \simeq π/4 - θ_C$. Such quark-lepton complementarity (QLC) may be a signal of an underlying quark-lepton unification at short distances. We discuss possible ways to realize this relation in realistic quark-lepton unification theories by identifying a minimal set of operators that lead to QLC while remaining consistent with other known data. The purpose of this paper is to present the first elements of a unified model at the GUT scale capable of predicting the QLC relation. A generic prediction of our proposed class of models is the new relation for the lepton mixing angle $θ_{13} \simeq θ_C$, which allows these models to be confirmed or excluded by the current generation of neutrino oscillation experiments.

hep-ph↗

arXiv2005

Dirac Neutrinos and Hybrid Inflation from String Theory

We consider a possible scenario for the generation of Dirac neutrino masses motivated by Type I string theory. The smallness of the neutrino Yukawa couplings is explained by an anisotropic compactification with one compactification radius larger than the others. In addition to this we utilise small Yukawa couplings to develop strong links between the origin of neutrino masses and the physics driving inflation. We construct a minimal model which simultaneously accommodates small Dirac neutrino masses leading to bi-large lepton mixing as well as an inflationary solution to the strong CP and to the $μ$ problem.

hep-ph↗

arXiv2005

Sneutrino Hybrid Inflation in Supergravity

We propose a hybrid inflation scenario in which the singlet sneutrino, the superpartner of the right-handed neutrino, plays the role of the inflaton. We study a minimal model of sneutrino hybrid inflation in supergravity, where we find a spectral index $n_s \approx 1 + 2 γ$ with $|γ| \lesssim 0.02$, and predict a running spectral index $|d n_s/d\ln k| \ll |γ|$ and a tensor-to-scalar ratio $r \ll γ^2$ for field values well below the Planck scale. In our scenario, the baryon asymmetry of our universe can be explained via non-thermal leptogenesis and a low reheat temperature $T_{RH} \approx 10^{6}$ GeV can be realized.

hep-ph↗

arXiv2005

From Hierarchical to Partially Degenerate Neutrinos via Type II Upgrade of Type I See-Saw Models

We propose a type II upgrade of type I see-saw models leading to new classes of models where partially degenerate neutrinos are as natural as hierarchical ones. The additional type II contribution to the neutrino mass matrix, which determines the neutrino mass scale, is forced to be proportional to the unit matrix by a SO(3) flavour symmetry. The type I see-saw part of the neutrino mass matrix, which controls the mass squared differences and mixing angles, may be governed by sequential right-handed neutrino dominance and a natural alignment for the SO(3)-breaking vacuum. We focus on classes of models with bi-large mixing originating from the neutrino mass matrix although we also briefly discuss other classes of models where large mixing stems from the charged lepton mass matrix. We study renormalization group corrections to the neutrino mass squared differences and mixings and find that the low energy values do not depend sensitively on the high energy values for partially degenerate neutrinos with a mass scale up to about 0.15 eV. Our scenario predicts the effective mass for neutrinoless double beta decay to be approximately equal to the neutrino mass scale and therefore neutrinoless double beta decay will be observable if the neutrino mass spectrum is partially degenerate. We also find that all observable CP phases as well as $θ_{13}$ become small as the neutrino mass scale increases.

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