40 research outputs found
Chiral corrections to the Gell-Mann-Oakes-Renner relation
The next to leading order chiral corrections to the
Gell-Mann-Oakes-Renner (GMOR) relation are obtained using the pseudoscalar
correlator to five-loop order in perturbative QCD, together with new finite
energy sum rules (FESR) incorporating polynomial, Legendre type, integration
kernels. The purpose of these kernels is to suppress hadronic contributions in
the region where they are least known. This reduces considerably the systematic
uncertainties arising from the lack of direct experimental information on the
hadronic resonance spectral function. Three different methods are used to
compute the FESR contour integral in the complex energy (squared) s-plane, i.e.
Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a
fixed renormalization scale scheme. We obtain for the corrections to the GMOR
relation, , the value . This result
is substantially more accurate than previous determinations based on QCD sum
rules; it is also more reliable as it is basically free of systematic
uncertainties. It implies a light quark condensate . As a byproduct, the chiral perturbation theory (unphysical) low energy
constant is predicted to be , or .Comment: A comment about the value of the strong coupling has been added at
the end of Section 4. No change in results or conslusion
Analysis of techni-dilaton as a dark matter candidate
The almost conformal dynamics of walking technicolor (TC) implies the
existence of the approximate scale invariance, which breaks down spontaneously
by the condensation of anti-techni and techni-fermions. According to the
Goldstone theorem, a spinless, parity-even particle, called techni-dilaton
(TD), then emerges at low energy. If TC exhibits an extreme walking, TD mass is
parametrically much smaller than that of techni-fermions (around 1 TeV), while
its decay constant is comparable to the cutoff scale of walking TC. We analyze
the light, decoupled TD as a dark matter candidate and study cosmological
productions of TD, both thermal and non-thermal, in the early Universe. The
thermal population is governed dominantly by single TD production processes
involving vertices breaking the scale symmetry, while the non-thermal
population is by the vacuum misalignment and is accumulated via harmonic and
coherent oscillations of misaligned classical TD fields. The non-thermal
population turns out to be dominant and large enough to explain the abundance
of presently observed dark matter, while the thermal population is highly
suppressed due to the large TD decay constant. Several cosmological and
astrophysical limits on the light, decoupled TD are examined to find that the
TD mass is constrained to be in a range between 0.01 eV and 500 eV. From the
combined constraints on cosmological productions and astrophysical
observations, we find that the light, decoupled TD can be a good dark matter
candidate with the mass around a few hundreds of eV for typical models of
(extreme) walking TC. We finally mention possible designated experiments to
detect the TD dark matter.Comment: 26 pages. 16 figures; v2, expanded Section 2.4 on composite Higgs in
light of newly discovered Higgs-like particle at LH
Broken R-Parity in the Sky and at the LHC
Supersymmetric extensions of the Standard Model with small R-parity and
lepton number violating couplings are naturally consistent with primordial
nucleosynthesis, thermal leptogenesis and gravitino dark matter. We consider
supergravity models with universal boundary conditions at the grand unification
scale, and scalar tau-lepton or bino-like neutralino as next-to-lightest
superparticle (NLSP). Recent Fermi-LAT data on the isotropic diffuse gamma-ray
flux yield a lower bound on the gravitino lifetime. Comparing two-body
gravitino and neutralino decays we find a lower bound on a neutralino NLSP
decay length, c \tau_{\chi^0_1} \gsim 30 cm. Together with gravitino and
neutralino masses one obtains a microscopic determination of the Planck mass.
For a stau-NLSP there exists no model-independent lower bound on the decay
length. Here the strongest bound comes from the requirement that the
cosmological baryon asymmetry is not washed out, which yields c
\tau_{\tilde\tau_1} \gsim 4 mm. However, without fine-tuning of parameters,
one finds much larger decay lengths. For typical masses,
and , the discovery of a photon line with an intensity
close to the Fermi-LAT limit would imply a decay length of
several hundred meters, which can be measured at the LHC.Comment: 30 pages, 8 figures; v2: published version, reference adde