arXiv subjects

O. Nachtmann

Publications and source records attributed to O. Nachtmann.

At least 19 recordsLinked to original sources

arXiv2026

Stability and Symmetry Breaking in the General Two-Higgs-Doublet Model

A method is presented for the analysis of the scalar potential in the general Two-Higgs-Doublet Model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the Two-Higgs-Doublet potential proposed by Gunion et al. The known results for these models follow easily as special cases from the general results. In particular, for the potential of Gunion et al. we can clarify the stability and symmetry breaking properties of the model with our method.

hep-ph↗

arXiv2025

CMS results for the $γγ$ production at the LHC: do they give a hint for a Higgs boson of the maximally CP symmetric two-Higgs-doublet model?

Recent measurements of the CMS experiment at the LHC show possibly, with about 3 $σ$ significance, a resonance in di-photon events with an invariant mass of 95.4 GeV. If this resonance can be confirmed, this could be a hint for a new elementary particle beyond the Standard Model. An additional Standard-model-like Higgs boson with this mass could be excluded by the CMS experiment. We investigate whether this resonance could fit into a two-Higgs-doublet model highly constrained by CP symmetry, the so-called maximally-CP-symmetric model (MCPM). In the strict symmetry limit of the MCPM only the fermions of the third generation obtain masses. We discuss a mechanism where the first and second generation fermions get masses through effects from interactions with very high mass particles. The latter can be integrated out at LHC energies giving effective Lagrangian terms, among them these mass terms. This procedure also gives us a Cabibbo-Kobayashi-Maskawa (CKM) matrix which automatically satisfies some salient structural features observed in experiments. We call the resulting theory MCPM'. Our finding shows that indeed the enhancement measured by CMS could originate from the pseudoscalar Higgs boson $h''$ of this model. According to the model the boson $h''$ would mainly be produced in the Drell-Yan reaction by charm-anticharm-quark fusion. The main decay mode of $h''$ is predicted to be $h'' \to c\bar{c}$. We then consider the so called oblique parameters $S$, $T$, $U$ which give us an allowed region for the mass of the scalar Higgs boson $h'$ versus that of the charged ones $H^\pm$ of the MCPM'. We calculate the effect of these charged bosons $H^\pm$ in the leptonic decays of the charm mesons $D^\pm$ and the charm-strange mesons $D_s^\pm$. Our results indicate that the mass $m_{H^\pm}$ of the charged Higgs bosons $H^\pm$ of the MCPM' should be around 300 GeV.

hep-ph↗

arXiv2019

Generalised P and CP transformations in the 3-Higgs-doublet model

We study generalised P and CP transformations in the three-Higgs-doublet model (3HDM) with Higgs and gauge fields only. We find that there are two equivalence classes, with respect to flavour transformations, of generalised P transformations and there is only one class of CP transformations. We discuss the conditions the potential has to satisfy in order to be invariant under these transformations. We apply the method of bilinears which we briefly review. We discuss the relation to the conventional basis, where the potential is written in terms of scalar products of the doublet fields. In particular we reproduce the known result that a potential is invariant under CP transformations if and only if there is a conventional basis where all parameters are real. Eventually we study standard P and CP transformations in the $n$-Higgs-doublet model (nHDM). We show that for the bilinears of the nHDM the standard CP transformation corresponds to a diagonal linear transformation with only $\pm 1$ as diagonal elements. We give this matrix explicitly for arbitrary $n$.

hep-ph↗

arXiv2016

The MCPM, a two-Higgs-doublet model with maximal CP symmetry, and LHC13

We continue our investigation of the phenomenological consequences of the MCPM for the LHC experiments. As in any two-Higgs-doublet model we have in the MCPM three neutral Higgs bosons and one charged Higgs-boson pair $H^\pm$. Here we discuss the two-photon production in proton-proton collisions. We find that in the MCPM a resonance-type structure in the $γγ$ invariant mass distribution is predicted around twice the $H^\pm$ mass $m_{H^\pm}$ with a width $2\; Γ_H$ where $Γ_H$ is the $H^\pm$ width. If we set $m_{H^\pm} = 375$ GeV, the above resonance structure appears at 750 GeV with a width of about 45 GeV. We point out various predictions of the MCPM which follow in such a scenario and which can be checked at the LHC.

hep-ph↗

arXiv2015

Stability and symmetry breaking in the general n-Higgs-doublet model

For potentials with n-Higgs-boson doublets stability, electroweak symmetry breaking, and the stationarity equations are discussed in detail. This is done within the bilinear formalism which simplifies the investigation, in particular since irrelevant gauge degrees of freedom are systematically avoided. For the case that the potential leads to the physically relevant electroweak symmetry breaking the mass matrices of the physical Higgs bosons are given explicitly.

hep-ph↗

arXiv2015

Stability and symmetry breaking in the general three-Higgs-doublet model

Stability, electroweak symmetry breaking, and the stationarity equations of the general three-Higgs-doublet model (3HDM) where all doublets carry the same hypercharge are discussed in detail. Employing the bilinear formalism the study of the 3HDM potential turns out to be straightforward. For the case that the potential leads to the physically relevant electroweak symmetry breaking we present explicit formulae for the masses of the physical Higgs bosons.

hep-ph↗

arXiv2012

Towards testing a two-Higgs-doublet model with maximal CP symmetry at the LHC: construction of a Monte Carlo event generator

A Monte Carlo event generator is constructed for a two-Higgs-doublet model with maximal CP symmetry, the MCPM. The model contains five physical Higgs bosons; the $ρ'$, behaving similarly to the standard-model Higgs boson, two extra neutral bosons $h'$ and $h"$, and a charged pair $H^\pm$. The special feature of the MCPM is that, concerning the Yukawa couplings, the bosons $h'$, $h"$ and $H^\pm$ couple directly only to the second generation fermions but with strengths given by the third-generation-fermion masses. Our event generator allows the simulation of the Drell-Yan-type production processes of $h'$, $h"$ and $H^\pm$ in proton-proton collisions at LHC energies. Also the subsequent leptonic decays of these bosons into the $μ^+ μ^-$, $μ^+ ν_μ$ and $μ^- \bar ν_μ$ channels are studied as well as the dominant background processes. We estimate the integrated luminosities needed in $p p$ collisions at center-of-mass energies of 8 TeV and 14 TeV for significant observations of the Higgs bosons $h'$, $h"$ and $H^\pm$ in these muonic channels.

hep-ph↗

arXiv2012

Metastable states of hydrogen: their geometric phases and flux densities

We discuss the geometric phases and flux densities for the metastable states of hydrogen with principal quantum number n=2 being subjected to adiabatically varying external electric and magnetic fields. Convenient representations of the flux densities as complex integrals are derived. Both, parity conserving (PC) and parity violating (PV) flux densities and phases are identified. General expressions for the flux densities following from rotational invariance are derived. Specific cases of external fields are discussed. In a pure magnetic field the phases are given by the geometry of the path in magnetic field space. But for electric fields in presence of a constant magnetic field and for electric plus magnetic fields the geometric phases carry information on the atomic parameters, in particular, on the PV atomic interaction. We show that for our metastable states also the decay rates can be influenced by the geometric phases and we give a concrete example for this effect. Finally we emphasise that the general relations derived here for geometric phases and flux densities are also valid for other atomic systems having stable or metastable states, for instance, for He with n=2. Thus, a measurement of geometric phases may give important experimental information on the mass matrix and the electric and magnetic dipole matrices for such systems. This could be used as a check of corresponding theoretical calculations of wave functions and matrix elements.

physics.atom-ph↗

arXiv2011

Symmetries and renormalisation in two-Higgs-doublet models

We discuss the classification of symmetries and the corresponding symmetry groups in the two-Higgs-doublet model (THDM). We give an easily useable method how to determine the symmetry class and corresponding symmetry group of a given THDM Higgs potential. One of the symmetry classes corresponds to a Higgs potential with several simultaneous generalised CP symmetries. Extending the CP symmetry of this class to the Yukawa sector in a straightforward way, the so-called maximally-CP-symmetric model (MCPM) is obtained. We study the evolution of the quartic Higgs-potential parameters under a change of renormalisation point. Finally we compute the so called oblique parameters S, T, and U, in the MCPM and we identify large regions of viable parameter space with respect to electroweak precision measurements. We present the corresponding allowed regions for the masses of the physical Higgs bosons. Reasonable ranges for these masses, up to several hundred GeV, are obtained which should make the (extra) Higgs bosons detectable in LHC experiments.

hep-ph↗

arXiv2010

Geometric picture of generalized-CP and Higgs-family transformations in the two-Higgs-doublet model

In the two-Higgs-doublet model (THDM), generalized-CP transformations (phi_i--> X_{ij} phi_j^* where X is unitary) and unitary Higgs-family transformations (phi_i--> U_{ij} phi_j) have recently been examined in a series of papers. In terms of gauge-invariant bilinear functions of the Higgs fields phi_i, the Higgs-family transformations and the generalized-CP transformations possess a simple geometric description. Namely, these transformations correspond in the space of scalar-field bilinears to proper and improper rotations, respectively. In this formalism, recent results relating generalized CP transformations with Higgs-family transformations have a clear geometric interpretation.

hep-ph↗

arXiv2010

On the phenomenology of a two-Higgs-doublet model with maximal CP symmetry at the LHC - synopsis and addendum

Predictions for LHC physics are given for a two-Higgs-doublet model having four generalized CP symmetries. In this maximally-CP-symmetric model (MCPM) the first fermion family is, at tree level, uncoupled to the Higgs fields and thus massless. The second and third fermion families have a very symmetric coupling to the Higgs fields. But through the electroweak symmetry breaking a large mass hierarchy is generated between these fermion families. Thus, the fermion mass spectrum of the model presents a rough approximation to what is observed in Nature. In the MCPM the couplings of the Higgs bosons to the fermions are completely fixed. This allows us to present clear predictions for the production at the LHC and for the decays of the physical Higgs bosons. As salient feature we find rather large cross sections for Higgs-boson production via Drell-Yan type processes. In this paper we present a short outline of the model and extend a former study by the predictions at LHC for a center-of-mass energy of 7 TeV.

hep-ph↗

arXiv2010

CP properties of symmetry-constrained two-Higgs-doublet models

The two-Higgs-doublet model can be constrained by imposing Higgs-family symmetries and/or generalized CP symmetries. It is known that there are only six independent classes of such symmetry-constrained models. We study the CP properties of all cases in the bilinear formalism. An exact symmetry implies CP conservation. We show that soft breaking of the symmetry can lead to spontaneous CP violation (CPV) in three of the classes.

hep-ph↗

arXiv2010

Longitudinal Atomic Beam Spin Echo Experiments: A possible way to study Parity Violation in Hydrogen

We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo (lABSE) apparatus. Depending on the choice of the external fields the atoms may acquire both dynamical and geometrical quantum mechanical phases. As an example of the former, we show first in-beam spin rotation measurements on atomic hydrogen, which are in excellent agreement with theory. Additional calculations of the behaviour of the metastable 2S states of hydrogen reveal that the geometrical phases may exhibit the signature of parity-(P-)violation. This invites for possible future lABSE experiments, focusing on P-violating geometrical phases in the lightest of all atoms.

physics.atom-ph↗

arXiv2009

On the phenomenology of a two-Higgs-doublet model with maximal CP symmetry at the LHC, II: radiative effects

The processes proton + antiproton -> gamma + heavy-flavour jet(s) + X and proton + proton -> gamma + heavy-flavour jet(s) + X are studied in the framework of a special two-Higgs-doublet model, the MCPM. As distinguishing feature of this model we find that radiative Higgs-boson production and decay lead to heavy flavour c jets but no b jets in the above processes. Thus, the prediction is that b jets should be given by the normal QCD processes whereas for c jets an excess over the QCD expectation should occur. We present results both for Tevatron and LHC energies.

hep-ph↗

arXiv2009

A computer controlled pendulum with position readout

We have designed, built and operated a physical pendulum which allows one to demonstrate experimentally the behaviour of the pendulum under any equation of motion for such a device for any initial conditions. All parameters in the equation of motion can be defined by the user. The potential of the apparatus reaches from demonstrating simple undamped harmonic oscillations to complex chaotic behaviour of the pendulum. The position data of the pendulum as well as derived kinematical quantities like velocity and acceleration can be stored for later offline analysis.

physics.pop-ph↗

arXiv2009

On the phenomenology of a two-Higgs-doublet model with maximal CP symmetry at the LHC

Predictions for LHC physics are worked out for a two-Higgs-doublet model having four generalized CP symmetries. In this maximally-CP-symmetric model (MCPM) the first fermion family is, at tree level, uncoupled to the Higgs fields and thus massless. The second and third fermion families have a very symmetric coupling to the Higgs fields. But through the electroweak symmetry breaking a large mass hierarchy is generated between these fermion families. Thus, the fermion mass spectrum of the model presents a rough approximation to what is observed in Nature. In the MCPM there are, as in every two-Higgs-doublet model, five physical Higgs bosons, three neutral ones and a charged pair. In the MCPM the couplings of the Higgs bosons to the fermions are completely fixed. This allows us to present clear predictions for the production at the LHC and for the decays of the physical Higgs bosons. As salient feature we find rather large cross sections for Higgs-boson production via Drell-Yan type processes. With experiments at the LHC it should be possible to check these predictions.

hep-ph↗

arXiv2008

Parity Violation in Hydrogen and Longitudinal Atomic Beam Spin Echo I

We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo (lABSE) apparatus. There the atoms acquire geometric (Berry) phases that exhibit a new manifestation of parity-(P-)violation in atomic physics. We provide analytical as well as numerical calculations of the behaviour of the metastable 2S states of hydrogen. The conditions for electromagnetic field configurations that allow for adiabatic evolution of the relevant atomic states are investigated. Our results provide the theoretical basis for the discussion of possible measurements of P-violating geometric phases in lABSE experiments.

physics.atom-ph↗

arXiv2008

A new type of CP symmetry, family replication and fermion mass hierarchies

We study a two-Higgs-doublet model with four generalised CP symmetries in the scalar sector. Electroweak symmetry breaking leads automatically to spontaneous breaking of two of them. We require that these four CP symmetries can be extended from the scalar sector to the full Lagrangian and call this requirement the principle of maximal CP invariance. The Yukawa interactions of the fermions are severely restricted by this requirement. In particular, a single fermion family cannot be coupled to the Higgs fields. For two fermion families, however, this is possible. Enforcing the absence of flavour-changing neutral currents, we find degenerate masses in both families or one family massless and one massive. In the latter case the Lagrangian is highly symmetric, with the mass hierarchy being generated by electroweak symmetry breaking. Adding a third family uncoupled to the Higgs fields and thus keeping it massless we get a model which gives a rough approximation of some features of the fermions observed in Nature. We discuss a number of predictions of the model which may be checked in future experiments at the LHC.

hep-ph↗