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Stefan Antusch

Publications and source records attributed to Stefan Antusch.

At least 91 records · Page 5Linked to original sources
arXiv2014

Hilltop inflation with preinflation from coupling to matter fields

We propose a class of models of supersymmetric hilltop inflation (also called "new inflation") where the initial conditions of the inflaton close to the hilltop are generated through "matter field preinflation". This is achieved via a coupling term between the inflaton and matter fields (i.e. Standard Model fields or a right-handed neutrino). The same coupling also opens up a decay channel for the inflaton into Standard Model fields, which allows efficient reheating of the universe. We discuss the multifield dynamics of the inflaton and matter fields during inflation using the delta N formalism and show under which conditions the model effectively reduces to single-field hilltop inflation during the last 60 e-folds. We also study perturbative reheating through the matter-inflaton coupling for a specific example where the matter field is identified with a right-handed (s)neutrino, and demonstrate that in this case the model can generate the observed baryon asymmetry through nonthermal leptogenesis.

hep-ph↗
arXiv2014

BICEP2 implications for single-field slow-roll inflation revisited

It is generally believed that in single-field slow-roll inflation, a large tensor-to-scalar ratio $r > 0.1$ requires inflaton field values close to or above the Planck scale. Recently, it has been claimed that $r > 0.15$ can be achieved with much smaller inflaton field values $Δϕ< M_{Pl}/10$. We show that in single-field slow-roll inflation, it is impossible to reconcile $r > 0.1$ with such small field values, independently of the form of the potential, and that the recent claim to the contrary is based on an invalid approximation. We conclude that the result of the BICEP2 measurement of $r > 0.1$, if confirmed, truly has the potential to rule out small-field models of single-field slow-roll inflation.

hep-ph↗
arXiv2013

Inverse neutrino mass hierarchy in a flavour GUT model

We construct a supersymmetric SU(5) x A_4 flavour GUT model in which an inverse neutrino mass hierarchy is realised without fine-tuning of parameters. The model shares some properties with the normal hierarchy model which we presented in arXiv:1305.6612 - in particular the relation theta_13^PMNS = theta_C / sqrt(2). Besides these shared features, there are also important differences, mainly due to the different neutrino sector. These differences not only change the predictions in the lepton sector, but also in the quark sector, and will allow to discriminate between the two models using the results of present and future experiments. From a Markov Chain Monte Carlo fit we find that the inverse hierarchy model is in excellent agreement with the present experimental data.

hep-ph↗
arXiv2013

SUGRA New Inflation with Heisenberg Symmetry

We propose a realisation of 'new inflation' in supergravity (SUGRA), where the flatness of the inflaton potential is protected by a Heisenberg symmetry. Inflation can be associated with a particle physics phase transition, with the inflaton being a (D-flat) direction of Higgs fields which break some symmetry at high energies, e.g. of GUT Higgs fields or of Higgs fields for flavour symmetry breaking. This is possible since compared to a shift symmetry, which is usually used to protect a flat inflaton potential, the Heisenberg symmetry is compatible with a (gauge) non-singlet inflaton field. In contrast to conventional new inflation models in SUGRA, where the predictions depend on unknown parameters of the K"ahler potential, the model with Heisenberg symmetry makes discrete predictions for the primordial perturbation parameters which depend only on the order n at which the inflaton appears in the effective superpotential. The predictions for the spectral index n_s can be close to the best-fit value of the latest Planck 2013 results.

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arXiv2013

Solving the Strong CP Problem with Discrete Symmetries and the Right Unitarity Triangle

We present a solution to the strong CP problem based on spontaneous CP violation and discrete family symmetries. The model predicts in a natural way the almost right-angled quark unitarity triangle angle ($α\simeq 90^\circ$) by making the entries of the quark mass matrices either real or imaginary. By this choice the determinants of the mass matrices are rendered real and hence the strong CP phase vanishes. We present a toy model for the quark sector that demonstrates the viability of our approach.

hep-ph↗
arXiv2013

A flavour GUT model with theta_13^PMNS = theta_C / sqrt(2)

We propose a supersymmetric SU(5) GUT model with an A_4 family symmetry - including a full flavon- and messenger sector - which realises the relation theta_13^PMNS \simeq theta_C / sqrt(2). The neutrino sector features tri-bimaximal mixing, and theta_13^PMNS \simeq theta_C / sqrt(2) emerges from the charged lepton contribution to the PMNS matrix, which in turn is linked to quark mixing via specific GUT relations. These GUT relations arise after GUT symmetry breaking from a novel combination of group theoretical Clebsch-Gordan factors, which in addition to large theta_13^PMNS lead to promising quark lepton mass ratios for all generations of quarks and leptons and to m_s / m_d = 18.95_(-0.24)^(+0.33), in excellent agreement with experimental results. The model also features spontaneous CP violation, with all quark and lepton CP phases determined from family symmetry breaking. We perform a full Markov Chain Monte Carlo fit to the available quark and lepton data, and discuss how the model can be tested by present and future experiments.

hep-ph↗
arXiv2013

Running quark and lepton parameters at various scales

We calculate the values and 1 sigma ranges of the running quark and lepton Yukawa couplings as well as of the quark mixing parameters at various energy scales, i.e. at M_Z, 1 TeV, 3 TeV, 10 TeV and at the GUT scale, to provide useful input for model building. Above TeV energies, we assume the minimal supersymmetric extension of the Standard Model, and include the tan(beta)-enhanced one-loop supersymmetric threshold corrections which arise when matching the SM to its SUSY extension. We calculate the GUT scale values of the running parameters as well as their 1 sigma ranges, with the supersymmetric threshold corrections included and with their effects parametrised in a simple way.

hep-ph↗
arXiv2013

Matter inflation with A_4 flavour symmetry breaking

We discuss model building in tribrid inflation, which is a framework for realising inflation in the matter sector of supersymmetric particle physics models. The inflaton is a D-flat combination of matter fields, and inflation ends by a phase transition in which some Higgs field obtains a vacuum expectation value. We first describe the general procedure for implementing tribrid inflation in realistic models of particle physics that can be applied to a wide variety of BSM particle physics models around the GUT scale. We then demonstrate how the procedure works for an explicit lepton flavour model based on an A_4 family symmetry. The model is both predictive and phenomenologically viable, and illustrates how tribrid inflation connects cosmological and particle physics parameters. In particular, it predicts a relation between the neutrino Yukawa coupling and the running of the spectral index alpha_s. We also show how topological defects from the flavour symmetry breaking can be avoided automatically.

hep-ph↗
arXiv2013

Spontaneous CP violation in A4xSU(5) with Constrained Sequential Dominance 2

We revisit a two right-handed neutrino model with two texture zeros, namely an indirect model based on A4 with the recently proposed new type of constrained sequential dominance (CSD2), involving vacuum alignments along the (0,1,-1)^T and (1,0,2)^T directions in flavour space, which are proportional to the neutrino Dirac mass matrix columns. In this paper we construct a renormalizable and unified indirect A4xSU(5) model along these lines and show that, with spontaneous CP violation and a suitable vacuum alignment of the phases, the charged lepton corrections lead to a reactor angle in good agreement with results from Daya Bay and RENO. The model predicts a right-angled unitarity triangle in the quark sector and a Dirac CP violating oscillation phase in the lepton sector of delta approximately 130 degrees, while providing a good fit to all quark and lepton masses and mixing angles.

hep-ph↗
arXiv2013

Naturalness of the Non-Universal MSSM in the light of the recent Higgs results

We analyse the naturalness of the Minimal Supersymmetric Standard Model (MSSM) in the light of recent LHC results from the ATLAS and CMS experiments. We study non-universal boundary conditions for the scalar and the gaugino sector, with fixed relations between some of the soft breaking parameters, and find a significant reduction of fine-tuning for non-universal gaugino masses. For a Higgs mass of about 125 GeV, as observed recently, we find parameter regions with a fine-tuning of O(10), taking into account experimental and theoretical uncertainties. These regions also survive after comparison with simplified model searches in ATLAS and CMS. For a fine-tuning less than 20 the lightest neutralino is expected to be lighter than about 400 GeV and the lighter stop can be as heavy as 3.5 TeV. On the other hand, the gluino mass is required to be above 1.5 TeV. For non-universal gaugino masses, we discuss which fixed GUT scale ratios can lead to a reduced fine-tuning and find that the recent Higgs results have a strong impact on which ratio is favoured. We also discuss the naturalness of GUT scale Yukawa relations, comparing the non-universal MSSM with the CMSSM.

hep-ph↗
arXiv2013

Kähler-driven Tribrid Inflation

We discuss a new class of tribrid inflation models in supergravity, where the shape of the inflaton potential is dominated by effects from the Kähler potential. Tribrid inflation is a variant of hybrid inflation which is particularly suited for connecting inflation with particle physics, since the inflaton can be a D-flat combination of charged fields from the matter sector. In models of tribrid inflation studied so far, the inflaton potential was dominated by either loop corrections or by mixing effects with the waterfall field (as in "pseudosmooth" tribrid inflation). Here we investigate the third possibility, namely that tribrid inflation is dominantly driven by effects from higher-dimensional operators of the Kähler potential. We specify for which superpotential parameters the new regime is realized and show how it can be experimentally distinguished from the other two (loop-driven and "pseudosmooth") regimes.

hep-ph↗
arXiv2012

Pseudosmooth Tribrid Inflation

We explore a new class of supersymmetric models of inflation where the inflaton is realised as a combination of a Higgs field and (gauge non-singlet) matter fields, using a "tribrid" structure of the superpotential. Inflation is associated with a phase transition around GUT scale energies. The inflationary trajectory already preselects the later vacuum after inflation, which has the advantage of automatically avoiding the production of dangerous topological defects at the end of inflation. While at first sight the models look similar to smooth inflation, they feature a waterfall and are therefore only pseudosmooth. The new class of models offers novel possibilities for realising inflation in close contact with particle physics, for instance with supersymmetric GUTs or with supersymmetric flavour models based on family symmetries.

hep-ph↗
arXiv2012

θ^PMNS_13 = θ_C / \sqrt2 from GUTs

The recent observations of the leptonic mixing angle θ^PMNS_13 are consistent with θ^PMNS_13 = θ_C / \sqrt2 (with θ_C being the Cabibbo angle θ^CKM_12). We discuss how this relation can emerge in Grand Unified Theories (GUTs) via charged lepton corrections. The key ingredient is that in GUTs the down-type quark Yukawa matrix and the charged lepton Yukawa matrix are generated from the same set of GUT operators, which implies that the resulting entries are linked and differ only by group theoretical Clebsch factors. This allows a link θ^e_12 = θ_C to be established, which can induce θ^PMNS_13 = θ_C / \sqrt2 provided that the 1-3 mixing in the neutrino mass matrix is much smaller than θ_C. We find simple conditions under which θ^PMNS_13 = θ_C / \sqrt2 can arise via this link in SU(5) GUTs and Pati-Salam models. We also discuss possible corrections to this relation. Using lepton mixing sum rules different neutrino mixing patterns can be distinguished by their predictions for the Dirac CP phase δ^PMNS.

hep-ph↗
arXiv2012

Naturalness and GUT Scale Yukawa Coupling Ratios in the CMSSM

We analyse the fine-tuning in the Constrained Minimal Supersymmetric Standard Model (CMSSM) in the light of the present and expected ATLAS and CMS SUSY searches. Even with 10/fb of data and no discovery of SUSY valid regions might remain with fine-tuning less than 20. Moreover we investigate the fine-tuning price of GUT scale Yukawa coupling relations. Considering a 2$σ$ constraint for $(g-2)_μ$ and fine-tuning less than 30 yields an allowed range of $y_τ/y_b = [1.31,1.70]$, which points towards the alternative GUT prediction $y_τ/y_b = 3/2$. Relaxing the $(g-2)_μ$ constraint to 5$σ$ extends the possible region to [1.02,1.70], allowing for approximate $b-τ$ Yukawa coupling unification.

hep-ph↗
arXiv2012

A fuller flavour treatment of N_2-dominated leptogenesis

We discuss N_2-dominated leptogenesis in the presence of flavour dependent effects that have hitherto been neglected, in particular the off-diagonal entries of the flavour coupling matrix that connects the total flavour asymmetries, distributed in different particle species, to the lepton and Higgs doublet asymmetries. We derive analytical formulae for the final asymmetry including the flavour coupling at the N_2-decay stage as well as at the stage of washout by the lightest right-handed neutrino N_1. Moreover, we point out that in general part of the electron and muon asymmetries (phantom terms), can completely escape the wash-out at the production and a total B-L asymmetry can be generated by the lightest RH neutrino wash-out yielding so called phantom leptogenesis. However, the phantom terms are proportional to the initial N_2 abundance and in particular they vanish for initial zero N_2-abundance. Taking any of these new effects into account can significantly modify the final asymmetry produced by the decays of the next-to-lightest RH neutrinos, opening up new interesting possibilities for N_2-dominated thermal leptogenesis.

hep-ph↗
arXiv2012

Large neutrino mixing angle θ_{13}^{MNS} and quark-lepton mass ratios in unified flavour models

We analyse how a large value of the leptonic mixing angle θ_{13}^{MNS} can be generated via charged lepton corrections in unified flavour models, using novel combinations of Clebsch-Gordan factors for obtaining viable quark-lepton mass ratios for the first two families. We discuss how these Clebsch-Gordan factors affect the relations between down-type quark mixing and charged lepton mixing in SU(5) GUTs and Pati-Salam unified models and calculate the resulting possible predictions for θ_{13}^{MNS} for models with θ_{13}^ν, θ_{13}^e << θ_{12}^e. While symmetric mass matrices with zero (1,1)-elements always lead to comparatively small θ_{13}^{MNS} \approx 2.8 degrees, we find novel combinations of Clebsch-Gordan factors for non-symmetric mass matrices which can yield θ_{13}^{MNS} \approx 5.1 degrees, 6.1 degrees, 7.6 degrees or 10.1 degrees, as favoured by the current experimental hints for large θ_{13}^{MNS}. We discuss applications to classes of models with underlying tri-bimaximal or bimaximal mixing in the neutrino sector.

hep-ph↗
arXiv2012

Combining High-scale Inflation with Low-energy SUSY

We propose a general scenario for moduli stabilization where low-energy supersymmetry can be accommodated with a high scale of inflation. The key ingredient is that the stabilization of the modulus field during and after inflation is not associated with a single, common scale, but relies on two different mechanisms. We illustrate this general scenario in a simple example, where during inflation the modulus is stabilized with a large mass by a Kahler potential coupling to the field which provides the inflationary vacuum energy via its F-term. After inflation, the modulus is stabilized, for instance, by a KKLT superpotential.

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