Effects Of New Interactions Research Articles

Effective-field theory analysis of the \u03c4\u2212 \u2192 \u03b7(\u2032)\u03c0\u2212\u03bd\u03c4 decays

The rare τ− → η(′)π−ντ decays, which are suppressed by G-parity in the Standard Model (SM), can be sensitive to the effects of new interactions. We study the sensitivity of different observables of these decays in the framework of an effective field theory that includes the most general interactions between SM fields up to dimension six, assuming massless neutrinos. Owing to the strong suppression of the SM isospin breaking amplitudes, we find that the different observables would allow to set constraints on scalar interactions that are stronger than those coming from other low-energy observables.

A set of top quark spin correlation and polarization observables for the LHC: Standard Model predictions and new physics contributions

We consider top-antitop quark ($t{\bar t}$) production at the Large Hadron Collider (LHC) with subsequent decay into dileptonic and lepton plus jets final states. We present a set of leptonic angular correlations and distributions with which experiments can probe all the independent coefficient functions of the top-spin dependent parts of the $t{\bar t}$ production spin density matrices. We compute these angular correlations and distributions for LHC center-of-mass energies 8, 13, and 14 TeV within the Standard Model at next-to-leading order in the QCD coupling including the mixed QCD-weak corrections and for the transverse top-quark polarization and the $t{\bar t}$ charge asymmetry also the mixed QCD-QED corrections. In addition we analyze and compute the effects of new interactions on these observables in terms of a gauge-invariant effective Lagrangian which contains all operators relevant for hadronic $t{\bar t}$ production up to mass dimension six.

Gauge string in the fermion asymmetric matter

Two new effects of interaction of the gauge string with a homogeneous density of fermions are considered in a gauge model with an anomalous coupling of vector fields with fermions. First, the presence of an induced nonzero magnetic-like helicity on the straight string is demonstrated. Second, it is shown that the equation of motion of the string is modified by a nonlinear term that can be decomposed into the correction to the string tension and an additional force perpendicular to the tangent and normal vectors of the string. Static configurations are found and their stability is studied.

Low energy effects of new interactions in the electroweak boson sector.

Novel strong interactions in the electroweak bosonic sector are expected to induce effective interactions between the Higgs doublet field and the electroweak gauge bosons which lead to anomalous $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ vertices once the Higgs field acquires a vacuum expectation value. Using a linear realization of the Goldstone bosons, we consider a complete set of dimension-six operators which are SU(2)\ifmmode\times\else\texttimes\fi{}U(1) gauge invariant and conserve $C$ and $P$. This approach allows us to study effects of new physics which originates above 1 TeV and the Higgs boson mass dependence of the results can be investigated. Four of the dimension-six operators affect low energy and present CERN LEP experiments at the tree level. Another five influence neutral and charged current experiments at the one-loop level and three of these lead to anomalous $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ vertices. Their loop contributions are at most logarithmically divergent, and these logarithmic divergences can be understood as renormalizations of the four operators which contribute at the tree level. Constraints on the remaining five operators can be obtained if one assumes the absence of cancellations between the tree level and one-loop contributions. The resulting bounds on anomalous triple gauge boson couplins are modest, which emphasizes the importance of direct measurements of the triple gauge boson vertices, e.g., in ${W}^{+}{W}^{\ensuremath{-}}$ production at LEP II.

Top and Higgs masses from vacuum leaks of the standard model

The vacuum expectation value of the gauge invariant component of the Higgs field of the standard model is a true, nonrunning constant. By considering its structure and by postulating that the coupling constants of the standard model are constrained to minimize the effects of new interactions at higher energies we obtain the Veltman condition and an additional mass formula. Both equations should be valid at the physical mass scale of these particles. We find m t ≅122 GeV, M H ≅195 GeV. If correct, the condensates of the field components of top, Higgs and vector bosons will have a universal strength estimated to be 3.1 TeV.

The τ→ν τηπ process in and beyond QCD

We estimate various sources of the τ→ν τηπ process by using QCD-duality sum rule information on the decay constants of standard and exotic mesons. We use the π→ l ν l decay in order to constrain the effects of new interactions. We conclude from our analysis that in al cases, the τ→ν τηπ branching ration is small. We also point out that the present data on the τ→νπ process already provide an upper limit of 0.1% on the ηπ mode while the τ→ν τKK̄ data imply an upper limit of 0.5% if the a 0 (980)- meson is a four-quark state.