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Dan Pirjol

Publications and source records attributed to Dan Pirjol.

At least 73 records · Page 4Linked to original sources
arXiv2006

Parity Doubling and SU(2)_L x SU(2)_R Restoration in the Hadron Spectrum

We construct the most general nonlinear representation of chiral SU(2)_L x SU(2)_R broken down spontaneously to the isospin SU(2), on a pair of hadrons of same spin and isospin and opposite parity. We show that any such representation is equivalent, through a hadron field transformation, to two irreducible representations on two hadrons of opposite parity with different masses and axial couplings. This implies that chiral symmetry realized in the Nambu-Goldstone mode does not predict the existence of degenerate multiplets of hadrons of opposite parity nor any relations between their couplings or masses.

hep-ph↗
arXiv2006

Factorization in B -> K pi e+e- decays

We derive factorization relations for the transverse helicity amplitudes in the rare decays B-> Kπl+l- at leading order in Lambda/m_b, in the kinematical region with an energetic kaon and a soft pion. We identify and compute a new contribution of leading order in Lambda/m_b to the B->Kπl+l- amplitude, which is not present in the one-body decay B-> K*l+l-. As an application we study the forward-backward asymmetry (FBA) of the lepton momentum angular distribution in B-> Kπl+l- decays away from the K* resonance. The FBA in these decays has a zero at q0^2 = q0^2(M_{Kpi}), which can be used, in principle, for determining the Wilson coefficients C_{7,9} and testing the Standard Model. We point out that the slope of the q0^2(M_{Kpi}^2) curve contains the same information about the Wilson coefficients as the location of the zero, but is less sensitive to unknown nonperturbative dynamics. We estimate the location of the zero at leading order in factorization, and using a resonant model for the B -> Kπl+l- nonfactorizable amplitude.

hep-ph↗
arXiv2006

Occupation number formalism for arbitrary Nc baryons

A general method is presented for computing matrix elements of quark operators on baryonic states with low strangeness and arbitrary number of colors Nc. These results are useful in applications of the large Nc expansion to baryons and exotics. As an application we compute the matrix elements of strangeness changing operators contributing to kaon couplings to ground state baryons and pentaquarks, in broken SU(3).

hep-ph↗
arXiv2006

Next to Minimal Flavor Violation

The flavor structure of a wide class of models, denoted as next to minimal flavor violation (NMFV), is considered. In the NMFV framework, new physics (NP), which is required for stabilization of the electroweak symmetry breaking (EWSB) scale, naturally couples (dominantly) to the third generation quarks and is quasi-aligned with the Yukawa matrices. Consequently, new sources of flavor and CP violation are present in the theory, mediated by a low scale of few TeV. However, in spite of the low flavor scale, the most severe bounds on the scale of NP are evaded since these are related to flavor violation in the first two generations. Instead, one typically finds that the NP contributions are comparable in size to SM loop processes. We argue that, in spite of the successful SM unitary triangle fit and contrary to the common lore, such a sizable contribution to Delta F=2 processes of ~ 40% (with arbitrary phase) compared to SM is presently allowed since B-factories are only beginning to constrain these models. Thus, it is very interesting that in the NMFV models one is not forced to separate the scale of NP related to EWSB and the scale of flavor violation. We show briefly that this simple setup includes a wide class of supersymmetric and non-supersymmetric models all of which solve the hierarchy problem. We further discuss tests related to Delta F=1 processes, in particular the ones related to b -> s transition. The b -> s processes are computed using two different hadronic models to estimate the uncertainties involved. In addition, we derive constraints on the NP from B -> Kpi data using only SU(3) flavor symmetry and minimal dynamical assumptions. Finally we argue that in many cases correlating Delta F=2 and Delta F=1 processes is a powerful tool to probe our framework.

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arXiv2006

The CP asymmetry in B^0(t) -> K_S π^0 γin the Standard Model

The time-dependent CP asymmetry in exclusive B^0(t) -> K^{*0}γdecays has been proposed as a probe of new physics in B decays. Recently, this method was extended to radiative decays into multibody hadronic final states such as B^0(t)-> K_Sπ^0γand B^0(t)-> π^+π^-γ. The CP asymmetry in these decays vanishes to the extent that the photon is completely polarized. In the Standard Model, the photon emitted in b-> sγhas high left-handed polarization, but right-handed contamination enters already at leading order in Λ/m_b even for vanishing light quark masses. We compute here the magnitude of this effect and the time dependent CP asymmetry parameter S_{K_S π^0γ}. We find that the Standard Model can easily accomodate values of S as large as 10%, but a precise value cannot be obtained at present because of strong interactions uncertainties.

hep-ph↗
arXiv2005

Testing the dynamics of B -> ππand constraints on α

In charmless nonleptonic B decays to ππor ρρ, the "color allowed" and "color suppressed" tree amplitudes can be studied in a systematic expansion in \alphas(mb) and Λ/mb. At leading order in this expansion their relative strong phase vanishes. The implications of this prediction are obscured by penguin contributions. We propose to use this prediction to test the relative importance of the various penguin amplitudes using experimental data. The present B->ππdata suggest that there are large corrections to the heavy quark limit, which can be due to power corrections to the tree amplitudes, large up-quark penguin amplitude, or enhanced weak annihilation. Because the penguin contributions are smaller, the heavy quark limit is more consistent with the B->ρρdata, and its implications may become important for the extraction of αfrom this mode in the future.

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arXiv2005

Factorization in exclusive semileptonic radiative B decays

We derive a new factorization relation for the semileptonic radiative decay B -> π\ell νγin the kinematical region of a slow pion p_π~ Λand an energetic photon E_γ>> Λ, working at leading order in Λ/m_b. In the limit of a soft pion, the nonperturbative matrix element appearing in this relation can be computed using chiral perturbation theory. We present a phenomenological study of this decay, which may be important for a precise determination of the exclusive nonradiative decay.

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arXiv2005

Theory of hadronic B decays

I give an overview of the theory of hadronic nonleptonic B decays into two light mesons. Using the soft-collinear effective theory (SCET), a factorization theorem for these processes has been proven to leading order in 1/mb. The phenomenological implications of this factorization relation for B-> ππdecays are discussed, together with the prospects for determining the weak phase α(ϕ_2) from these modes.

hep-ph↗
arXiv2005

Chiral symmetry and exclusive B decays in the SCET

We describe a chiral formalism for processes involving both energetic hadrons and soft Goldstone bosons, which extends the application of soft-collinear effective theory to multibody B decays. The nonfactorizable helicity amplitudes for heavy meson decays into multibody final states satisfy symmetry relations analogous to the large energy form factor relations, which are broken at leading order in Lambda/mb by calculable factorizable terms. We use the chiral effective theory to compute the leading corrections to these symmetry relations in B -> M_n pi ell\barνand B -> M_n pi e+e- decays.

hep-ph↗
arXiv2005

Negative parity pentaquarks in large Nc QCD and quark model

Recently, the 1/Nc expansion has been applied to the study of exotic baryons containing both quarks and antiquarks. We extend this approach to exotic states with mixed symmetric spin-flavor symmetry, which correspond in the quark model to negative parity pentaquarks, and discuss the large Nc predictions for their mass spectrum. The heavy exotics Qbar q^4 transform as 3, 6bar,15 and 15' under flavor SU(3), while the light states include the exotic multiplets 10bar, 27, 35. We give mass relations among these multiplets following from the 1/Nc expansion. In the quark model, the mass splittings between these states are given by color-spin interactions. Using the observation of an anticharmed exotic by the H1 collaboration, we give predictions for the masses of other expected heavy pentaquarks.

hep-ph↗
arXiv2005

On Differences Between SCET and QCDF for B->pi pi Decays

We give a detailed description of the differences between the factorization and results derived from SCET and QCDF for decays B -> M1 M2. This serves as a reply to a comment about our work "B-> M1 M2: Factorization, charming penguins, strong phases, and polarization" [1] made by the authors in [2]. We disagree with their criticisms.

hep-ph↗
arXiv2005

Graphical amplitudes from SCET

We discuss the relationship between the graphical amplitudes T, C, P, ... used to parameterize nonleptonic B decay amplitudes, and matrix elements of operators in the soft-collinear effective theory (SCET) at leading order in Λ/m_b. Using the SU(3) flavor symmetry of the weak Hamiltonian we derive all-order constraints on the electroweak penguin contributions to the Wilson coefficients of SCET operators.

hep-ph↗
arXiv2004

The photon polarization in B -> X gamma in the standard model

The standard model prediction for the $B\to X_{s,d}γ$ decay amplitude with a right-handed photon is believed to be tiny, suppressed by $m_{s,d}/m_b$, compared to the amplitude with a left-handed photon. We show that this suppression is fictitious: in inclusive decays, the ratio of these two amplitudes is only suppressed by $g_s/(4π)$, and in exclusive decays by $Λ_{QCD}/m_b$. The suppression is not stronger in $B\to X_dγ$ decays than it is in $B\to X_sγ$. We estimate that the time dependent CP asymmetries in $B\to K^*γ$, $ργ$, $K_Sπ^0γ$, and $π^+π^-γ$ are of order 0.1 and that they have significant uncertainties.

hep-ph↗
arXiv2004

Exclusive rare B -> K*e+e- decays at low recoil: controlling the long-distance effects

We present a model-independent description of the exclusive rare decays B-> K* e+e- in the low recoil region (large lepton invariant mass q^2 ~ m_b^2). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in 1/Q, with Q={m_b, \sqrt{q^2}}. Nonperturbative effects up to and including terms suppressed by Lambda/Q and mc^2/mb^2 relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the CKM matrix element |V{ub}| from a combination of rare and semileptonic B and D decays near the zero recoil point. The residual theoretical uncertainty from long distance effects in this |V{ub}| determination comes from terms in the OPE of order alpha_s(Q)Λ/mb, alpha_s^2(Q), mc^4/mb^4$ and duality violations and is estimated to be below 10%.

hep-ph↗
arXiv2004

B -> M1 M2: Factorization, Charming Penguins, Strong Phases, and Polarization

Using the soft-collinear effective theory we derive the factorization theorem for the decays B-> M1 M2 with M{1,2}= pi,K, rho,K*, at leading order in Lambda/E_M and Lambda/mb. The results derived here apply even if alpha_s(E_M Lambda) is not perturbative, and we prove that the physics sensitive to the E*Lambda scale is the same in B-> M1 M2 and B-> M form factors. We argue that c-cbar penguins could give long-distance effects at leading order. Decays to two transversely polarized vector mesons are discussed. Analyzing B-> pi pi we find predictions for B^0 -> pi^0 pi^0 and |V_{ub}| f_+(0) as a function of gamma.

hep-ph↗
arXiv2004

Factorization and the Soft-Collinear Effective Theory: Color-Suppressed Decays

We discuss the soft-collinear effective theory (SCET) and kinematic expansions in B-decays, focusing on recent results for color suppressed B -> D^(*) X decays. In particular we discuss model independent predictions for B^0 -> D^0 pi^0 and B^0 -> D^*0 pi^0, and update the comparison using new experimental data. We show why HQET alone is insufficient to give these results. SCET predictions are also reviewed for other B and Lambda_b decay channels that are not yet tested by data.

hep-ph↗
arXiv2003

The phenomenology of rare and semileptonic B decays

We summarize recent progress in the theory of exclusive rare and semileptonic B decays, focusing on model-independent results. The heavy-to-light form factors parameterizing these decays admit a model-independent description in two distinct kinematical regions. In the large-energy limit of an energetic light meson, the Soft-Collinear Effective Theory can be used to prove factorization formulas for the form factors. We present factorization formulas for all B-> P,V form factors at leading order in Lambda/m_b. Near the zero-recoil point, Heavy Quark Effective Theory gives useful relations among the form factors of different currents.

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