Bohdan Grzadkowski

Dimension-Six Terms in the Standard Model Lagrangian ⋆

When the Standard Model is considered as an effective low-energy theory, higher dimensional interaction terms appear in the Lagrangian. Dimension-six terms have been enumerated in the classical article by Buchmüller and Wyler [3]. Although redundance of some of those operators has been already noted in the literature, no updated complete list has been published to date. Here we perform their classification once again from the outset. Assuming baryon number conservation, we find 15 + 19 + 25 = 59 independent operators (barring flavour structure and Hermitian conjugations), as compared to 16 + 35 + 29 = 80 in ref. [3]. The three summed numbers refer to operators containing 0, 2 and 4 fermion fields. If the assumption of baryon number conservation is relaxed, 5 new operators arise in the four-fermion sector.

Multi-scalar-singlet extension of the standard model — The case for dark matter and an invisible Higgs boson

We consider a simple extension of the Standard Model by the addition of N real scalar gauge singlets

Pragmatic approach to the little hierarchy problem: the case for dark matter and neutrino physics.

\overrightarrow \varphi

Two-Component Dark Matter

that are candidates for Dark Matter. By collecting theoretical and experimental constraints we determine the space of allowed parameters of the model. The possibility of ameliorating the little hierarchy problem within the multisinglet model is discussed. The Spergel-Steinhardt solution of the Dark Matter density cusp problem is revisited. It is shown that fitting the recent CRESST-II data for Dark Matter nucleus scattering implies that the standard Higgs boson decays predominantly into pairs of Dark Matter Scalars. In that case discovery of the Higgs boson at LHC and Tevatron is impossible. The most likely mass of the dark scalars is in the range 15 GeV ≾ m φ ≾ 50 GeV with BR(

Natural Multi-Higgs Model with Dark Matter and CP Violation

h \to \overrightarrow \varphi \overrightarrow \varphi

The bilinear formalism and the custodial symmetry in the two-Higgs-doublet model

) up to 96%.

Tempered two-Higgs-doublet model

We show that the addition of real scalars (gauge singlets) to the standard model can both ameliorate the little hierarchy problem and provide realistic dark matter candidates. To this end, the coupling of the new scalars to the standard Higgs boson must be relatively strong and their mass should be in the 1-3 TeV range, while the lowest cutoff of the (unspecified) UV completion must be > or ~ 5 TeV, depending on the Higgs boson mass and the number of singlets present. The existence of the singlets also leads to realistic, and surprisingly reach, neutrino physics. The resulting light neutrino mass spectrum and mixing angles are consistent with the constraints from the neutrino oscillations.

Higgs-radion interpretation of the LHC data?

A bstractWe study an extension of the Standard Model (SM) with two interacting cold Dark Matter (DM) candidates: a neutral Majorana fermion (ν) and a neutral scalar singlet (φ). The scalar φ interacts with the SM through the “Higgs portal” coupling while ν at the tree level interacts only with φ through Yukawa interactions. The relic abundance of ν and φ is found by solving the Boltzmann equations numerically; for the case mν > mφ we also derive a reliable approximate analytical solution. Effects of the interaction between the two DM components are discussed. A scan over the parameter space is performed to determine the regions consistent with the WMAP data for DM relic abundance, and with the XENON100 direct detection limits for the DM-nucleus cross section. We find that although a large region of the parameter space is allowed by the WMAP constraints, the XENON100 data severely restricts the parameter space. Taking into account only amplitudes generated at the tree level one finds three allowed regions for the scalar mass: mφ ~ 62.5 GeV (corresponding to the vicinity of the Higgs boson resonance responsible for φφ annihilation into SM particles), mφ ≃ 130 − 140 GeV and mφ ≳ 3 TeV. 1-loop induced ν-nucleon scattering has been also calculated and discussed. A possibility of DM direct detection by the CREST-II experiment was considered.

Natural Two-Higgs-Doublet Model

We explore an extension of the inert doublet model which allows also for CP violation in the Higgs sector. This necessitates two noninert doublets. The lightest neutral scalar of the inert doublet is a candidate for dark matter. Scanning over parameters we preserve the abundance of the dark matter in agreement with the WMAP data. We also impose all relevant collider and theoretical constraints to determine the allowed parameter space for which both the dark matter is appropriate and CP is violated. In addition we find regions where the cutoff of the model originating from naturality arguments can be substantially lifted compared to its standard model value, reaching {approx}2-3 TeV.

Exploring the CP-violating Inert-Doublet Model

A bstractWe present a simple and transparent analysis of custodial symmetry in the Two-Higgs-Doublet Model adopting the bilinear formalism for the Higgs potential. The method allows to derive basis-independent, necessary and sufficient conditions for the potential to be invariant under custodial transformations. The relation between the custodial transformation and CP is revisited and clarified.Bohdan.Grzadkowski@fuw.edu.pl Maniatis@physik.uni-bielefeld.de jose.wudka@ucr.edu where L,R ∈ SU(2)L,R respectively. In the SM one can assume without loss of generality that the vacuum expectation value of φ is real, whence, after spontaneous symmetry breaking (SSB), 〈M〉 ∝ 12, so SU(2)L × SU(2)R is broken to SU(2)diag (the diagonal subgroup) and it is the invariance of |Dμφ| with respect to SU(2)diag that insures ρ = 1 at tree-level [2, 3]. The term custodial symmetry is reserved in the literature for the SU(2)diag transformations under which both would-be Goldstone bosons and the corresponding gauge bosons transform as triplets. In this work we will also refer to custodial transformations (CT) as those generated by the full group SU(2)L × SU(2)R. We will always assume that the vacuum respects the diagonal SU(2), the CS. Now we can write