160 research outputs found
Generalized messengers of supersymmetry breaking and the sparticle mass spectrum
We investigate the sparticle spectrum in models of gauge-mediated
supersymmetry breaking. In these models, supersymmetry is spontaneously broken
at an energy scale only a few orders of magnitude above the electroweak scale.
The breakdown of supersymmetry is communicated to the standard model particles
and their superpartners by "messenger" fields through their ordinary gauge
interactions. We study the effects of a messenger sector in which the
supersymmetry-violating F-term contributions to messenger scalar masses are
comparable to the supersymmetry-preserving ones. We also argue that it is not
particularly natural to restrict attention to models in which the messenger
fields lie in complete SU(5) GUT multiplets, and we identify a much larger
class of viable models. Remarkably, however, we find that the superpartner mass
parameters in these models are still subject to many significant contraints.Comment: 24 pages, LaTeX, uses epsf.sty, 4 figures. Assumptions clarified,
numerical bounds tweaked, typos correcte
One-loop corrections to the metastable vacuum decay
We evaluate the one-loop prefactor in the false vacuum decay rate in a theory
of a self interacting scalar field in 3+1 dimensions. We use a numerical
method, established some time ago, which is based on a well-known theorem on
functional determinants. The proper handling of zero modes and of
renormalization is discussed. The numerical results in particular show that
quantum corrections become smaller away from the thin-wall case. In the
thin-wall limit the numerical results are found to join into those obtained by
a gradient expansion.Comment: 31 pages, 7 figure
Superconformal Flavor Simplified
A simple explanation of the flavor hierarchies can arise if matter fields
interact with a conformal sector and different generations have different
anomalous dimensions under the CFT. However, in the original study by Nelson
and Strassler many supersymmetric models of this type were considered to be
'incalculable' because the R-charges were not sufficiently constrained by the
superpotential. We point out that nearly all such models are calculable with
the use of a-maximization. Utilizing this, we construct the simplest
vector-like flavor models and discuss their viability. A significant constraint
on these models comes from requiring that the visible gauge couplings remain
perturbative throughout the conformal window needed to generate the
hierarchies. However, we find that there is a small class of simple flavor
models that can evade this bound.Comment: 43 pages, 1 figure; V3: small corrections and clarifications,
references adde
On a Light Spinless Particle Coupled to Photons
A pseudoscalar or scalar particle that couples to two photons but not
to leptons, quarks and nucleons would have effects in most of the experiments
searching for axions, since these are based on the coupling.
We examine the laboratory, astrophysical and cosmological constraints on
and study whether it may constitute a substantial part of the dark matter. We
also generalize the interactions to possess gauge
invariance, and analyze the phenomenological implications.Comment: LaTex, 20p., 6 figures. Changes in sections 4, 5 and figure 2, our
bounds are now more stringent. To be published in Physical Review
Constraints on Very Light Axions from Cavity Experiments
In view of the ongoing galactic (or cosmic) axion detection experiments, we
compare the axion-photon-photon coupling 's for various
invisible (or very light) axion models.Comment: LaTeX, 1 eps figure include
Hadronic decay, the renormalization group, analiticity of the polarization operators and QCD parameters
The ALEPH data on hadronic tau-decay is throughly analysed in the framework
of QCD. The perturbative calculations are performed in 1-4-loop approximation.
The analytical properties of the polarization operators are used in the whole
complex q^2 plane. It is shown that the QCD prediction for R_{tau} agrees with
the measured value R_{tau} not only for conventional Lambda^{conv}_3 =
(618+-29) MeV but as well as for Lambda^{new}_3 = (1666+-7) MeV. The
polarization operator calculated using the renormgroup has nonphysical cut
[-Lambda^2_3, 0]. If Lambda_3 = Lambda^{conv}_3, the contribution of only
physical cut is deficient in the explanation of the ALEPH experiment. If
Lambda_3 = Lambda^{new}_3 the contribution of nonphysical cut is very small and
only the physical cut explains the ALEPH experiment. The new sum rules which
follow only from analytical properties of polarization operators are obtained.
Basing on the sum rules obtained, it is shown that there is an essential
disagreement between QCD perturbation theory and the tau-lepton hadronic decay
experiment at conventional value Lambda_3. In the evolution upwards to larger
energies the matching of r(q^2) (Eq.(12)) at the masses J/psi, Upsilon and 2m_t
was performed. The obtained value alpha_s(-m^2_z) = 0.141+-0.004 (at Lambda_3 =
Lambda^{new}_3) differs essentially from conventional value, but the
calculation of the values R(s) = sigma(e+e- -> hadrons)/sigma(e+e- -> mu+mu-),
R_l = Gamma(Z -> hadrons)/Gamma(Z -> leptons), alpha_s(-3 GeV^2), alpha_s(-2.5
GeV^2) does not contradict the experiments.Comment: 20 page
A Solution to the Strong CP Problem with Gauge-Mediated Supersymmetry Breaking
We demonstrate that a certain class of low scale supersymmetric
``Nelson-Barr'' type models can solve the strong and supersymmetric CP problems
while at the same time generating sufficient weak CP violation in the
system. In order to prevent one-loop corrections to
which violate bounds coming from the neutron electric dipole
moment (EDM), one needs a scheme for the soft supersymmetry breaking parameters
which can naturally give sufficient squark degeneracies and proportionality of
trilinear soft supersymmetry-breaking parameters to Yukawa couplings. We show
that a gauge-mediated supersymmetry breaking sector can provide the needed
degeneracy and proportionality, though that proves to be a problem for generic
Nelson-Barr models. The workable model we consider here has the Nelson-Barr
mass texture enforced by a gauge symmetry; one also expects a new U(1) gauge
superfield with mass in the TeV range. The resulting model is predictive. We
predict a measureable neutron EDM and the existence of extra vector-like quark
superfields which can be discovered at the LHC. Because the
Cabbibo-Kobayashi-Maskawa matrix is approximately real, the model also predicts
a flat unitarity triangle and the absence of substantial CP violation in the
system at future factories. We discuss the general issues pertaining to
the construction of such a workable model and how they lead to the successful
strategy. A detailed renormalization group study is then used to establish the
feasibility of the model considered.Comment: Proof-read version to appear in Phys. Rev.
Renormalization Group Approach to Field Theory at Finite Temperature
Scalar field theory at finite temperature is investigated via an improved
renormalization group prescription which provides an effective resummation over
all possible non-overlapping higher loop graphs. Explicit analyses for the
lambda phi^4 theory are performed in d=4 Euclidean space for both low and high
temperature limits. We generate a set of coupled equations for the mass
parameter and the coupling constant from the renormalization group flow
equation. Dimensional reduction and symmetry restoration are also explored with
our improved approach.Comment: 29 pages, can include figures in the body of the text using epsf.st
Searching for spatial variations of alpha^2/mu in the Milky Way
(Abridged) A procedure is suggested to explore the value of F = alpha^2/mu,
where mu = m_e/m_p is the electron-to-proton mass ratio, and alpha is the
fine-structure constant. The fundamental physical constants, which are measured
in different physical environments of high (terrestrial) and low (interstellar)
densities of baryonic matter are supposed to vary in chameleon-like scalar
field models, which predict that both masses and coupling constant may depend
on the local matter density. The parameter Delta F/F = (F_obs - F_lab)/F_lab
can be estimated from the radial velocity offset, Delta V = V_rot-V_fs, between
the low-laying rotational transitions in carbon monoxide 13CO and the
fine-structure transitions in atomic carbon [CI]. A model-dependent constraint
on Delta alpha/alpha can be obtained from Delta F/F using Delta mu/mu
independently measured from the ammonia method. Currently available radio
astronomical datasets provide an upper limit on |Delta V| < 110 m/s (1sigma).
When interpreted in terms of the spatial variation of F, this gives |Delta F/F|
< 3.7*10^-{7}. An order of magnitude improvement of this limit will allow us to
test independently a non-zero value of Delta mu/mu = (2.2 +/- 0.4_stat +/-
0.3_sys)*10^{-8} recently found with the ammonia method. Taking into account
that the ammonia method restricts the spatial variation of mu at the level of
|Delta mu/mu| <= 3*10^{-8} and assuming that Delta F/F is the same in the
entire interstellar medium, one obtains that the spatial variation of alpha
does not exceed the value |Delta alpha/alpha| < 2*10^{-7}. Since extragalactic
gas clouds have densities similar to those in the interstellar medium, the
bound on Delta alpha/alpha is also expected to be less than 2*10^{-7} at high
redshift if no significant temporal dependence of alpha is present.Comment: 7 pages, 1 table. Accepted for publication in Astronomy and
Astrophysic
ZFITTER v.6.21 - A Semi-Analytical Program for Fermion Pair Production in e+e- Annihilation
We describe ZFITTER, a Fortran program based on a semi-analytical approach to
fermion pair production in e+e- annihilation at a wide range of centre-of-mass
energies, including the PETRA, TRISTAN, LEP1/SLC, and LEP2 energies. A flexible
treatment of complete O(alpha) QED corrections and of some higher order
contributions is made possible with three calculational chains containing
different realistic sets of restrictions in the photon phase space. Numerical
integrations are at most one-dimensional. Complete O(alpha) weak loop
corrections supplemented by selected higher-order terms may be included. The
program calculates Delta r, the Z width, differential cross-sections, total
cross-sections, integrated forward-backward asymmetries, left-right
asymmetries, and for tau pair production also final-state polarization effects.
Various interfaces allow fits to be performed with different sets of free
parameters.Comment: 200 pages, Latex2e, 26 figures, 4 tables; uses axodraw, epsfig, epsf,
graphicx, espcrc1; typos of v.1 corrected, version for subm. to Comp. Phys.
Commu
- âŠ