arXiv subjects

J. O. Eeg

Publications and source records attributed to J. O. Eeg.

At least 19 recordsLinked to original sources

arXiv2012

Non-leptonic decays in an extended chiral quark model

We consider the color suppressed (nonfactorizable) amplitude for the decay mode $\bar{B_{d}^0} \rightarrow π^0 π^{0} $. We treat the $b$-quark in the heavy quark limit and the energetic light ($u,d,s$) quarks within a variant of Large Energy Effective Theory combined with an extension of chiral quark models. Our calculated amplitude for $\bar{B_{d}^0} \rightarrow π^0 π^{0} $ is suppressed by a factor of order $Λ_{QCD}/m_b$ with respect to the factorized amplitude, as it should according to QCD-factorization. Further, for reasonable values of the (model dependent) gluon condensate and the constituent quark mass, the calculated nonfactorizable amplitude for $\bar{B_{d}^0} \rightarrow π^0 π^{0} $ can easily accomodate the experimental value. Unfortunately, the color suppressed amplitude is very sensitive to the values of these model dependent parameters. Therefore fine-tuning is necessary in order to obtain an amplitude compatible with the experimental result for $\bar{B_{d}^0} \rightarrow π^0 π^{0} $.

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arXiv2006

Soft gluon contributions to the B --> K eta' amplitude in a low energy bosonization model

Intriguing B --> K eta' decays provide a unique opportunity to study a joining of two-gluon configurations arising from the penguin b --> sG and b --> sGG transitions, with those inherent to the eta' particle. We employ the heavy-light chiral quark model, applied previously to a somewhat related B --> D eta' decay, as a calculational tool accounting for the nonperturbative soft gluon contributions to the amplitude at hand. Thereby we arrive at a novel contribution to the singlet penguin amplitude, which within our model accounts for ~ 10 % of the measured B --> K eta' amplitude.

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arXiv2005

Non-factorizable contributions to $\bar{B^0_d} \to D_s^{()} \bar{D_s^{()}}$ from chiral loops and tree level $1/N_c$ terms

We point out that the amplitudes for the decays $\bar{B}^0 \to D_s^+ D_s^-$ and $\bar{B}^0_s \to D^+ D^-$ have no factorizable contributions. If one or two of the $D$-mesons in the final state are vectors (i.e $D^*$ 's) there are relatively small factorizable contributions through the annihilation mechanism. The dominant contributions to the decay amplitudes arise from chiral loop contributions and $1/N_c$ suppressed tree level. We predict that the branching ratios for the processes $\bar B^0_d \to D_s^+ D_s^-$, $\bar B^0_d \to D_s^{+*} D_s^- $ and $\bar B^0_d \to D_s^+ D_s^{-*}$ are all of order $(2- 3) \times 10^{-4}$, while $\bar B^0_s \to D_d^+ D_d^-$, $\bar B^0_s \to D_d^{+*} D_d^- $ and $\bar B^0_s \to D_d^+ D_d^{-*}$ are of order $(4- 7) \times 10^{-3}$. If {\em both} $D$-mesons in the final state are $D^*$'s, we obtain branching ratios of order two times bigger.

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arXiv2004

Non-factorizable contributions to $\bar{B^0_d} \to D_s^{()} \bar{D_s^{()}}$

It is pointed out that decays of the type $B \to D \bar{D}$ have no factorizable contributions, unless at least one of the charmed mesons in the final state is a vector meson. The dominant contributions to the decay amplitudes arise from chiral loop contributions and tree level amplitudes generated by soft gluon emissions forming a gluon condensate. We predict that the branching ratios for the processes $\bar B^0 \to D_s^+ D_s^-$, $\bar B^0 \to D_s^{+*} D_s^- $ and $\bar B^0 \to D_s^+ D_s^{-*}$ are all of order $(3- 4) \times 10^{-4}$, while $\bar B^0 \to D_s^{+*} D_s^{-*}$ has a branching ratio 5 to 10 times bigger. We emphasize that the branching ratios are sensitive to $1/m_c$ corrections.

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arXiv2004

On the Singlet Penguin in B --> K eta' decay

New contributions to the short-distance b --> s eta' transition are considered. They correspond to the quark and gluon content of eta'. Although substantially larger than the referent QCD anomaly tail, they still cannot account for the observed eta' enhancement.

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arXiv2003

Nonfactorizable contributions in anti-B0 -> Ds+ Ds- and anti-Bs0 -> D+ D- decays

The decay amplitudes for anti-B0 -> Ds+ Ds- and anti-Bs0 -> D+ D- have no factorizable contributions. We suggest that dominant contributions to the decay amplitudes arise from two chiral loop contributions and one soft gluon emission contribution. Then we determine branching ratios BR(anti-B0 -> Ds+ Ds-) ~ 7E-5 and BR(anti-Bs0 -> D+ D-) ~ 1E-3.

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arXiv2003

On the Short Distance Part of the QCD Anomaly Contribution to the b --> s eta' Amplitude

In addressing the B --> eta' K puzzle, there has been a considerable hope in the literature to resolve it by the QCD anomaly contribution to the b --> s eta' amplitude. This contribution corresponds to the electroweak b --> s g* g* transition followed by the off-shell gluon fusion g* g* --> eta'. In the present paper we perform a critical reassessment of this issue. We show that for the hard virtual gluons in a loop there is a well defined short distance amplitude corresponding to a remnant of the QCD anomaly. However, we find that it cannot account for the measured amplitude. In addition, we point out that the reduction of the gluon fusion vertex for the off-shell gluons is compensated by an absence of the claimed suppression in the electroweak vertex, and that some nonperturbative contributions related to the QCD anomaly may still be viable in explaining the physical B --> eta' K amplitude.

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arXiv2003

The β-term for D^* --> D γwithin a heavy-light chiral quark model

We present a calculation of the β-term for D^* --> D gamma within a heavy-light chiral quark model. Within the model, soft gluon effects in terms of the gluon condensate with lowest dimension are included. Also, calculations of 1/m_c corrections are performed. We find that the value of βis rather sensitive to the constituent quark mass compared to other quantities calculated within the same model. Also, to obtain a value close to the experimental value, one has to choose a constituent light quark mass larger than for other quantities studied in previous papers. For a light quark mass in the range 250 to 300 MeV and a quark condensate in the range -(250-270 MeV)^3 we find the value (2.5 +- 0.6) GeV^-1. This value is in agreement with the value of βextracted from experiment 2.7 +- 0.2 GeV^-1.

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arXiv2003

On the Colour Suppressed Decay Modes B^0 --> D_s^+ D_s^- and B_s^0 --> D^+ D^-

We point out that the decay modes B^0 --> D_s^+ D_s^- and B_s^0 --> D^+ D^- have no factorized contribution. At quark level these dacays can only proceed through the annihilation mechanism, which in the factorized limit give zero amplitude due to current conservation. In this paper, we identify the dominating non-factorizable (colour suppressed) contributions in terms of two chiral loop contributions and one soft gluon emission contribution. The latter contribution can be calculated in terms of the (lowest dimension) gluon condensate within a recently developed heavy-light chiral quark model. We find braching ratios BR(B^0 --> D_s^+ D_s^-) = 7*10^-5 and BR(B^0_s --> D^+ D^-) = 1*10^-3.

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arXiv2003

Non-factorizable effects in B-anti-B mixing

We study the B-parameter (``bag factor'') for B-anti-B mixing within a recently developed heavy-light chiral quark model. Non-factorizable contributions in terms of gluon condensates and chiral corrections are calculated. In addition, we also consider 1/m_Q corrections within heavy quark effective field theory. Perturbative QCD effects below μ= m_b known from other work are also included. Considering two sets of input parameters, we find that the renormalization invariant B-parameter is B = 1.51 +- 0.09 for B_d and B = 1.40 +- 0.16 for B_s.

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arXiv2002

A Heavy-Light Chiral Quark Model

We present a new chiral quark model for mesons involving a heavy and a light (anti-) quark. The model relates various combinations of a quark - meson coupling constant and loop integrals to physical quantities. Then, some quantities may be predicted and some used as input. The extension from other similar models is that the present model includes the lowest order gluon condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^- and the 1^- heavy meson states. Within the model, we find a reasonable description of parameters such as the decay constants f_B and f_D, the Isgur-Wise function and the axial vector coupling g_A in chiral perturbation theory for light and heavy mesons.

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arXiv2002

The double radiative annihilation of the heavy-light fermion bound states

We consider the double-radiative decays of heavy-light QED and QCD atoms, $μ^+ e^- \to γγ$ and $\bar{B}^{0}_s \to γγ$. Especially, we take under scrutiny contributions coming from operators that vanish on the free-quark mass shell. We show that by field redefinitions these operators are converted into contact terms attached to the bound state dynamics. A net off-shell contribution is suppressed with respect to the effect of the well known flavour-changing magnetic-moment operator by the bound-state binding factor. The negligible off-shellness of the weakly bound QED atoms becomes more relevant for strongly bound QCD atoms. We analyze this off-shellness in model-approaches to QCD, one of them enabling us to keep close contact to the related effect in QED. We also comment on the off-shell effect in the corresponding process $\bar{B}_d \to K^* γ$, and discuss possible hindering of the claimed beyond-standard-model discovery in this decay mode.

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arXiv2001

A gluonic mechanism for B --> D eta'

We present a calculation of the process B --> D eta' within a heavy-light chiral quark model. We assume that the eta' has a large gluonic component, and its coupling is described via the glue-glue-eta' effective vertex. The main contribution comes from the non-factorizable part of the effective weak Lagrangian at quark level. We find, within our model-dependent assumptions, a branching ratio Br(B --> D eta') = (1.7 -- 3.3) 10^(-4), somewhat below the experimental upper bound 9.4 10^(-4).

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arXiv2001

Nonfactorizable contributions to the decay mode D^0 -> K^0 \bar{K^0}

We point out that the decay mode D^0 -> K^0 \bar{K^0} has no factorizable contribution. In the chiral perturbation language, treating D^0 as heavy, the O(p) contribution is zero. We calculate the nonfactorizable chiral loop contributions of order O(p^3). Then, we use a heavy-light type chiral quark model to calculate nonfactorizable tree level terms, also of order O(p^3), proportional to the gluon condensate. We find that both the chiral loops and the gluon condensate contributions are of the same order of magnitude as the experimental amplitude.

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arXiv2000

Theoretical estimate(s) of the CP-violating quontity epsilon-prime/epsilon in K -> 2 pi decays

I give a short presentation of the theoretical prediction of epsilon-prime/epsilon. Short distance and especially long distance aspects of the computation is discussed. I consentrate on the general framework and the chiral quark model approach, while other approaches are also shortly presented. Because of the intrinsic uncertainties of the long-distance computations, it is unlikely that new physics effects can be disentangled from the standard model prediction.

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arXiv2000

Bound-state effects in μ^+ e^- \to γγand \bar{B}^{0}_s \to γγdecays

We demonstrate that in the double-radiative decays of heavy-light QED and QCD atoms, μ^{+} e^{-} \to γγand \bar{B}^{0}_{s} \to γγ, there is a contribution coming from operators that vanish on the free-quark mass shell. This off-shell effect is suppressed with respect to the effect of the well known flavour-changing magnetic-moment operator by the bound-state binding factor. Accordingly, the negligible off-shellness of the weakly bound QED atoms becomes important for strongly bound QCD atoms. We present this effect in two different model-approaches to QCD, one of them enabling us to keep close contact to the related effect in QED.

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arXiv1999

Estimating epsilon'/epsilon. A Review

The real part of epsilon'/epsilon measures direct CP violation in the decays of the neutral kaons in two pions. It is a fundamental quantity which has justly attracted a great deal of theoretical as well as experimental work. Its determination may answer the question of whether CP violation is present only in the mass matrix of neutral kaons (the superweak scenario) or also at work directly in the decays. After a brief historical summary, we discuss the present and expected experimental sensitivities. In the light of these, we come to the problem of estimating epsilon'/epsilon in the standard model. We review the present (circa 1998) status of the theoretical predictions of epsilon'/epsilon. The short-distance part of the computation is now known to the next-to-leading order in QCD and QED and therefore well under control. On the other hand, the evaluation of the hadronic matrix element of the relevant operators is where most of the theoretical uncertainty still resides. We analyze the results of the currently most developed calculations. The values of the B_i parameters in the various approaches are discussed, together with the allowed range of the relevant combination of the Cabibbo-Kobayashi-Maskawa entries Im V_{td}V^*_{ts}. We conclude by summarizing and comparing all up-to-date predictions of epsilon'/epsilon. Because of the intrinsic uncertainties of the long-distance computations, values ranging from 10^{-4} to a few times 10^{-3} can be accounted for in the standard model. Since this range covers most of the present experimental uncertainty, it is unlikely that new physics effects can be disentangled from the standard model prediction. For updates on the review and additional material see http://www.he.sissa.it/review/.

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arXiv1999

Long vs. short distance dispersive two-photon K_L \to μ^+ μ^- amplitude

We report on the calculation of the two-loop electroweak, two-photon mediated short-distance dispersive K_L \to μ^+μ^- decay amplitude. QCD corrections change the sign of this contribution and reduce it by an order of magnitude. The resulting amplitude enables us to provide a constraint on the otherwise uncertain long-distance dispersive amplitude.

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