10 research outputs found
A screening mechanism for extra W and Z gauge bosons
We generalize a previous construction of a fermiophobic model to the case of
more than one extra and gauge bosons. We focus in particular on the
existence of screening configurations and their implication on the gauge boson
mass spectrum. One of these configurations allows for the existence of a set of
relatively light new gauge bosons, without violation of the quite restrictive
bounds coming from the parameter. The links with Bess and
degenerate Bess models are also discussed. Also the signal given here by this
more traditional gauge extension of the SM could help to disentangle it from
the towers of Kaluza-Klein states over and gauge bosons in extra
dimensions.Comment: 23 pages, 1 figure, extended discussion on precision tests. To appear
in International Journal of Modern Physics
Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential
We address the issue of the reconstruction of the scalar potential of a
two-Higgs doublet model having in mind that of the MSSM.
We first consider the general CP conserving dim-4 effective potential. To
fully reconstruct this potential, we show that even if all the Higgs masses and
their couplings to the standard model particles are measured one needs not only
to measure certain trilinear Higgs self-couplings but some of the quartic
couplings as well. We also advocate expressing the Higgs self couplings in the
mass basis. We show explicitly, that in the so-called decoupling limit, the
most easily accessible Higgs self-couplings are given in terms of the Higgs
mass while all other dependencies on the parameters of the general effective
potential are screened. This helps also easily explain how, in the
MSSM, the largest radiative corrections which affect these self couplings are
reabsorbed by using the corrected Higgs mass. We also extend our analysis to
higher order operators in the effective Higgs potential. While the above
screening properties do not hold, we argue that these effects must be small and
may not be measured considering the foreseen poor experimental precision in the
extraction of the SUSY Higgs self-couplings.Comment: 25 pages, 3 figure
Extra dimensions at the one loop level: Z -> b,b(bar) and B-B(bar) mixing
We study, at the one loop level, the dominant new physics contributions from
extra dimensions to Z -> b,b(bar), as well as B-B(bar) and K-K(bar) mixing. We
use a model with one extra dimension containing fermions which live in four
dimensions, and gauge bosons and one scalar doublet propagating in five
dimensions. We find that the effect of the infinite tower of Kaluza-Klein modes
in Z-> b,b(bar) is finite and gives a negative correction to
R_b=Gamma_b/Gamma_h, which is used to set a lower bound of 1 TeV on the
compactification scale M_c. On the other hand, we show that the box diagrams
contributing to B-B(bar) and K-K(bar) mixing are divergent and, after proper
regularization, we find that they increase the value of the function S(x_t)
which governs this mixing. The obtained value is perfectly compatible with
available data.Comment: 14 pages, 3 figures, revte
The Goldstone boson equivalence theorem with fermions
The calculation of the leading electroweak corrections to physical transition
matrix elements in powers of can be greatly simplified in the limit
through the use of the Goldstone boson equivalence
theorem. This theorem allows the vector bosons and to be replaced
by the associated scalar Goldstone bosons , which appear in the
symmetry breaking sector of the Standard Model in the limit of vanishing gauge
couplings. In the present paper, we extend the equivalence theorem
systematically to include the Yukawa interactions between the fermions and the
Higgs and Goldstone bosons of the Standard Model. The corresponding Lagrangian
is given, and is formally renormalized to all orders. The
renormalization conditions are formulated both to make connection with physical
observables and to satisfy the requirements underlying the equivalence theorem.
As an application of this framework, we calculate the dominant radiative
corrections to fermionic Higgs decays at one loop including the virtual effects
of a heavy top quark. We apply the result to the decays
and , and find that the equivalence theorem results
including fermions are quite accurate numerically for Higgs-boson masses GeV, respectively, even for GeV.Comment: 32 pages, uses LaTeX2e, epsf and rotate, 7 figures included as
separate uuencoded packed file. A complete PostScript version can also be
obtained from
http://www.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/TUM-HEP-227-95.ps.g
Dynamical Left-Right Symmetry Breaking
We study a left--right symmetric model which contains only elementary gauge
boson and fermion fields and no scalars. The phenomenologically required
symmetry breaking emerges dynamically leading to a composite Higgs sector with
a renormalizable effective Lagrangian. We discuss the pattern of symmetry
breaking and phenomenological consequences of this scenario. It is shown that a
viable top quark mass can be achieved for the ratio of the VEVs of the
bi--doublet =~ 1.3--4. For a theoretically
plausible choice of the parameters the right--handed scale can be as low as
; in this case one expects several intermediate and low--scale
scalars in addition to the \SM Higgs boson. These may lead to observable lepton
flavour violation effects including decay with the rate close
to its present experimental upper bound.Comment: 51 pages, LaTeX and uuencoded, packed Postscript figures. The
complete paper, including figures, is also available via WWW at
http://www.cip.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/
TUM-HEP-222-95.ps.g