118612372
NLO corrections to timelike and spacelike DVCS
Generalized Parton Distributions (GPDs) offer a new way to access the quark and gluon nucleon structure. We advocate the need to supplement the experimental study of deeply virtual Compton scattering by its crossed version, timelike Compton scattering. We review recent progress in this domain, emphasizing the need to include NLO corrections to any phenomenological program to extract GPDs from experimental data.
53961130
Exploring the nucleon structure through GPDs and TDAs in hard exclusive processes
Generalized Parton Distributions (GPDs) offer a new way to access the quark and gluon nucleon structure. We review recent progress in this domain, emphasizing the need to supplement the experimental study of deeply virtual Compton scattering by its crossed version, timelike Compton scattering. We also describe the extension of the GPD concept to three quark operators and the relevance of their nucleon to meson matrix elements, namely the transition distribution amplitudes (TDAs) which factorize in backward meson electroproduction and related processes. We discuss the main properties of the TDAs. \
14804272
New results in exclusive hard reactions
Generalized Parton Distributions offer a new way to access the quark and gluon nucleon structure. We review recent progress in this domain, emphasizing the need to supplement the experimental study of DVCS by its crossed version, timelike Compton scattering (TCS), where data at high energy should appear thanks to the study of ultraperipheral collisions at the LHC. This will open the access to very low skewness quark and gluon GPDs. Our leading order estimates show that the factorization scale dependence of the amplitudes is quite high. This fact demands the understanding of higher order contributions with the hope that they will stabilize this scale dependence. The magnitudes of the NLO coefficient functions are not small and neither is the difference of the coefficient functions appearing respectively in the DVCS and TCS amplitudes. The conclusion is that extracting the universal GPDs from both TCS and DVCS reactions requires much care. We also describe the extension of the GPD concept to three quark operators and the relevance of their nucleon to meson matrix elements, namely the transition distribution amplitudes (TDAs) which factorize in hard exclusive pion electroproduction off a nucleon in the backward region and baryon-antibaryon annihilation into a pion and a lepton pair. We discuss the main properties of the TDAs.
119295664
On Timelike Compton Scattering at Medium and High Energies
We emphasize the complementarity of timelike and spacelike studies of deep exclusive processes, taking as an example the case of timelike Compton scattering (TCS) i.e. the exclusive photoproduction of a lepton pair with large invariant mass, versus deeply virtual Compton scattering i.e. the exclusive leptoproduction of a real photon. Both amplitudes factorize with the same generalized parton distributions (GPDs) as their soft parts and coefficient functions which differ significantly at next to leading order in αs. We also stress that data on TCS at very high energy should be available soon thanks to the study of ultraperipheral collisions at the LHC, opening a window on quark and gluon GPDs at very small skewness.
2626731
(Non)decoupling of the Higgs triplet effects
We consider the electroweak theory with an additional Higgs triplet at one loop, using the hybrid renormalization scheme based on αEM, GF and MZ as input observables. We show that in this scheme loop corrections can in a natural way be split into a standard model part and corrections due to “new physics”. The latter, however, do not decouple in the limit of an infinite triplet mass parameter, if the triplet trilinear coupling to the SM Higgs doublets grows with the triplet mass. For electroweak observables computed at one loop this effect can be attributed to the radiative generation in this limit of a nonvanishing vacuum expectation value of the triplet. We also point out that whenever tree level expressions for the electroweak observables depend on vacuum expectation values of scalar fields other than the standard model Higgs doublet, a tadpole contribution to the “oblique” parameter T should in principle be included. The origin of nondecoupling is discussed also on the basis of symmetry principles in a simple scalar field theory.
119565994
Violation of the Appelquist-Carazzone decoupling in non-SUSY GUT
We point out that in non supersymmetric GUTs, in which the SU(5) gauge symmetry is broken down to the Standard Model gauge group by a 24 Higgs multiplet the Appelquist-Carazzone decoupling is violated. This is because the SU(2)L Higgs triplet contained in the 24 acquires a dimensionfull coupling to the SU(2)L Higgs doublets which is proportional to the GUT breaking vacuum expectation value (VEV) V . As a result, at one loop heavy gauge and Higgs fields contribution to tadpoles generate a VEV of the triplet which is not suppressed for V → ∞ and violates the custodial symmetry.
118906401
Timelike Compton Scattering - New Theoretical Results and Experimental Possibilities
We review recent progress in the study of timelike Compton scattering (TCS), the crossed process of deeply virtual Compton scattering. We emphasize the need to include NLO corrections to any phenomenological program to extract Generalized Parton Distributions (GPDs) from near future experimental data. We point out that TCS at high energy should be available through a study of ultraperipheral collisions at RHIC and LHC, opening a window on quark and gluon GPDs at very small skewness.
5234726
Electroweak symmetry breaking in supersymmetric models with heavy scalar superpartners
Abstract We propose a novel mechanism of electroweak symmetry breaking in supersymmetric models, as the one recently discussed by Birkedal, Chacko and Gaillard, in which the Standard Model Higgs doublet is a pseudo-Goldstone boson of some global symmetry. The Higgs mass parameter is generated at one-loop level by two different, moderately fine-tuned sources of the global symmetry breaking. The mechanism works for scalar superpartner masses of order 10 TeV, but gauginos can be light. The scale at which supersymmetry breaking is mediated to the visible sector has to be low, of order 100 TeV. Fine-tuning in the scalar potential is at least two orders of magnitude smaller than in the MSSM with similar soft scalar masses. The physical Higgs boson mass is (for tan β ≫ 1 ) in the range 120 – 135  GeV .