The SCET_II and factorization

We reformulate the soft-collinear effective theory which includes the collinear quark and soft gluons. The quark form factor is used to prove that SCET$_{\rm II}$ reproduces the IR physics of the full theory. We give a factorization proof in deep inelastic lepton-hadron scattering by use of the position space formulation.Comment: 14 pages. The revised version which modifies largely will appear in PL

Nonleptonic B decays into two light mesons in soft-collinear effective theory

We consider nonleptonic B decays into two light mesons at leading order in soft-collinear effective theory, and show that the decay amplitudes are factorized to all orders in alpha_s. The operators for nonleptonic B decays in the full theory are first matched to the operators in SCET_I, which is the effective theory appropriate for sqrt{m_b Lambda} <mu <m_b with Lambda~0.5 GeV. We evolve the operators and the relevant time-ordered products in SCET_I to SCET_II, which is appropriate for mu < sqrt{m_b Lambda}. Using the gauge-invariant operators in SCET_II, we compute nonleptonic B decays in SCET, including the nonfactorizable spectator contributions and spectator contributions to the heavy-to-light form factor. As an application, we present the decay amplitudes for B ->pi,pi in soft-collinear effective theory.Comment: 42 pages, 5 figures, 2 tables Major revision of the manuscript. The idea of using SCET_I, and SCET_II is clearly presented. Some of the calculational steps are explicitly show

Power corrections in heavy-to-light decays at large recoil energy

I briefly present recent work on QCD power corrections in heavy-to-light meson decays, using an effective field theory approach.Comment: 4 pages, 1 figure. Talk given at ICHEP 2002, Amsterdam, July 200

Reparameterization Invariance for Collinear Operators

We discuss restrictions on operators in the soft-collinear effective theory (SCET) which follow from the ambiguity in the decomposition of collinear momenta and the freedom in the choice of light-like basis vectors $n$ and $\bar n$. Invariance of SCET under small changes in $n$ and/or $\bar n$ implies a symmetry of the effective theory that constrains the form of allowed operators with collinear fields. The restrictions occur at a given order in the power counting as well as between different orders. As an example, we present the complete set of higher order operators that are related to the collinear quark kinetic term.Comment: 11 page

Microscopic Approach to Nucleon Spectra in Hypernuclear Non-Mesonic Weak Decay

A consistent microscopic diagrammatic approach is applied for the first time to the calculation of the nucleon emission spectra in the non-mesonic weak decay of Lambda-hypernuclei. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one--meson exchange weak transition potential and a Bonn nucleon-nucleon strong potential. Ground state correlations and final state interactions, at second order in the nucleon--nucleon interaction, are introduced on the same footing for all the isospin channels of one- and two-nucleon induced decays. Single and double--coincidence nucleon spectra are predicted for 12_Lambda^C and compared with recent KEK and FINUDA data. The key role played by quantum interference terms allows us to improve the predictions obtained with intranuclear cascade codes. Discrepancies with data remain for proton emission.Comment: 11 pages, 6 figures, 2 tables. To be published in Physics Letters

Infrared regulators and SCETII

We consider matching from SCETI, which includes ultrasoft and collinear particles, onto SCETII with soft and collinear particles at one loop. Keeping the external fermions off their mass shell does not regulate all IR divergences in both theories. We give a new prescription to regulate infrared divergences in SCET. Using this regulator, we show that soft and collinear modes in SCETII are sufficient to reproduce all the infrared divergences of SCETI. We explain the relationship between IR regulators and an additional mode proposed for SCETII.Comment: 9 pages. Added discussion about relationship between IR regulators and messenger mode

The cosmological constant and the relaxed universe

We study the role of the cosmological constant (CC) as a component of dark energy (DE). It is argued that the cosmological term is in general unavoidable and it should not be ignored even when dynamical DE sources are considered. From the theoretical point of view quantum zero-point energy and phase transitions suggest a CC of large magnitude in contrast to its tiny observed value. Simply relieving this disaccord with a counterterm requires extreme fine-tuning which is referred to as the old CC problem. To avoid it, we discuss some recent approaches for neutralising a large CC dynamically without adding a fine-tuned counterterm. This can be realised by an effective DE component which relaxes the cosmic expansion by counteracting the effect of the large CC. Alternatively, a CC filter is constructed by modifying gravity to make it insensitive to vacuum energy.Comment: 6 pages, no figures, based on a talk presented at PASCOS 201

SCET approach to top quark decay

In this work we study QCD corrections to the top quark doubly decay rate with a detected $B$ hadron containing a $b$ quark. We focus on the regime among which the emitted $W$ boson nearly carries its maxim energy. The tool that we use here is the soft-collinear effective theory (SCET). The factorization theorem based on SCET indicates a novel fragmenting jet function. We calculate this function to next-to-leading order in $\alpha_s$. Large logarithms due to several well separated scale are summed up using the renormalization group equation (RGE). Finally we reach an analytic formula for the distribution which could easily be generalized to other heavy hadron decay.Comment: 13 pages, 4 figure

On the effect of the Delta(1232) in hypernuclear non-mesonic weak decay: a microscopic approach

The non-mesonic weak decay of $\Lambda$-hypernuclei is studied within a microscopic diagrammatic approach which includes, for the first time, the effect or the $\Delta$-baryon resonance. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one-meson exchange weak transition potential, a Bonn nucleon-nucleon strong potential and a $\Delta N\to NN$ strong potential based on the Landau-Migdal theory. Ground state correlations and final state interactions (FSI), at second order in the baryon-baryon strong interaction, are introduced on the same footing for all the isospin channels of one- and two-nucleon induced decays. Weak decay rates and single and double-coincidence nucleon spectra are predicted for $^{12}_\Lambda$C and compared with recent KEK and FINUDA data. The $\Delta(1232)$ introduces new FSI-induced decay mechanisms which lead to an improvement when comparing the obtained nucleon spectra with data, while it turns out to have a negligible effect on the decay rates. Discrepancies with experiment remain only for emission spectra involving protons, but are mostly restricted to double-nucleon correlations in the non-back-to-back kinematics.Comment: 11 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:1103.227

Nuclear Multifragmentation Critical Exponents

We show that the critical exponents of nuclear multi-fragmentation have not been determined conclusively yet.Comment: 3 pages, LaTeX, one postscript figure appended, sub. to Phys.Rev.Lett. as a commen