Chaotic inflation,radiative corrections and precision cosmology

We employ chaotic (?²${?}^2$ and ?⁴${?}^4$) inflation to illustrate the important role radiative corrections can play during the inflationary phase. Yukawa interactions of ?  , in particular, lead to corrections of the form −κ?⁴ln(?/μ)$-\kappa {?}^4\ln (?/\mu )$, where κ>0$\kappa >0$ and μ   is a renormalization scale. For instance, ?⁴${?}^4$ chaotic inflation with radiative corrections looks compatible with the most recent WMAP (5 year) analysis, in sharp contrast to the tree level case. We obtain the 95% confidence limits 2.4×¹⁰⁻¹⁴?κ?5.7×¹⁰⁻¹⁴$2.4\times {10}^{\mathrm{-14}}?\kappa ?5.7\times {10}^{\mathrm{-14}}$, 0.931?ns?0.958$0.931?n_s?0.958$ and 0.038?r?0.205$0.038?r?0.205$, where ns$n_s$ and r   respectively denote the scalar spectral index and scalar to tensor ratio. The limits for ?²${?}^2$ inflation are κ?7.7×¹⁰⁻¹⁵$\kappa ?7.7\times {10}^{\mathrm{-15}}$, 0.929?ns?0.966$0.929?n_s?0.966$ and 0.023?r?0.135$0.023?r?0.135$. The next round of precision experiments should provide a more stringent test of realistic chaotic ?²${?}^2$ and ?⁴${?}^4$ inflation.     

Infinite order radiative corrections and renormalization

By means of the Ward identity and the correlation expansion derived earlier, we calculate virtual radiative corrections to an infinite order. Partial factorization of the correlation effects, as in the simple exchange processes, makes infinite summation possible. Furthermore, because the Ward identity is satisfied order by order and because we are able to carry out the infinite order summation and obtain a closed form, renormalization turns out to be very simple and transparent. Here the calculations are performed for a scalar: ?²: φ model, but are easily generalized to other similar models. We also indicate why this rearrangement of the ordinary perturbation expansion is suitable for strong coupling theories, ordinary local field theories as well as dual models.     

Electroweak radiative corrections and quark mass singularities

A consistent method to remove quark mass singularities from physical cross sections is demonstrated. They are factorised into quark and gluon distribution functions. This implies electromagnetic correction terms to theQ ² dependent structure functions. They are calculated in leading order in the fine structure constant α and found to be flat and small overx.     

Higgs sector radiative corrections and s-channel production

Higgs boson mass sum rules of supersymmetric models offer attractive targets for precision tests at future muon colliders. These sum rules involve the gauge boson masses as well as the masses of the Higgs boson states which can be precisely measured in the s-channel production process at a muon collider. These measurements can sensitively probe radiative corrections to the Higgs boson masses as well as test for CP violation and nonminimality of the Higgs sector.     

Self-energy and vertex radiative corrections in LQG

We consider the elementary radiative-correction terms in loop quantum gravity. These are a two-vertex “elementary bubble” and a five-vertex “ball”; they correspond to the one-loop self-energy and the one-loop vertex correction of ordinary quantum field theory. We compute their naive degree of (infrared) divergence.     

Electroweak radiative corrections to muon capture

Electroweak radiative corrections to muon capture on nuclei are computed and found to be sizable. They enhance the capture rates for hydrogen and helium by 2.8% and 3.0%, respectively. As a result, the value of the induced pseudoscalar coupling, g(P)(exp), extracted from a recent hydrogen 1S singlet capture experiment is increased by about 21% to g(P)(exp)=7.3+/-1.2 and brought into good agreement with the prediction of chiral perturbation theory, g(P)(theory)=8.2+/-0.2. Implications for helium capture rate predictions are also discussed.     

Self-energy radiative corrections in hydrogen-like systems

The one-photon self-energy radiative level shift of an electron in a Coulomb field is examined. An expression for the level shift which is suitable for direct numerical evaluation, for Z in the range 10–110, is obtained. It is based on the known Coulomb radial Green's functions and not on a power series expansion in Zα. In the following paper, the numerical evaluation of the level shift for the $\text{1S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ state is described.     

More radiative corrections for β-decay

A calculation is performed of a hitherto ignored “radiative” correction to neutron β-decay. Conventional electromagnetism does not allow η → 3π decay; the mechanism responsible for this decay will lead to a correction to β-decay not taken into account by the standard O(α/π) coreection of one-photon exchange. While an order of magnitude estimate indicates this correction could in principle compete with the one-photon-exchange correction, explicit calculation puts it at three orders of magnitude down. Thus the agreement between the Cabibbo cosθ and the sinθ obtained from ΔS = 1 decays remains unspoilt.     

Using radiative corrections to bound substructure

Composite models predict the existence of excited quarks and leptons. We find bounds for the masses of possible excited leptons and for the substructure scale by using radiative corrections at theZ scale. A non-decoupling scenario arises naturally which induces upper bounds on these masses as a function of the substructure scale.     

QED radiative corrections to impact factors

We consider radiative corrections to the electron and photon impact factors. The generalized eikonal representation for the e ⁺ e ^? scattering amplitude at high energies and fixed momentum transfers is violated by nonplanar diagrams. An additional contribution to the two-loop approximation appears from the Bethe-Heitler mechanism of fermion pair production with the identity of the fermions in the final state taken into account. The violation of the generalized eikonal representation is also related to the charge parity conservation in QED. A one-loop correction to the photon impact factor for small virtualities of the exchanged photon is obtained using the known results for the cross section of the e ⁺ e ^? production during photon-nuclei interactions.     

Decays of intermediate vector bosons,radiative corrections and QCD jets

We investigate decay properties of the intermediate vector bosons W^± and Z⁰. QED and QCD radiative corrections to leptonic and hadronic decay modes are calculated. Implications of the results for decay widths, branching ratios, determination of the number of neutrino species, e-μ-τ universality and properties of hadronic jets produced in W^± and Z⁰ decays are examined.