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Jan O. Eeg

Publications and source records attributed to Jan O. Eeg.

18 recordsLinked to original sources
arXiv2022

Building the Standard Model Historical and Qualitative Aspects

Without going to the details, I give a short, qualitative and historical description of the development of the Standard Model, from quantum electrodynamics, further through quantum chromodynamics, then to weak interactions with parity- and CP-violation, ending up with electroweak symmetry breaking and the Higgs boson. The presentation is based on my own experiences from the late 1960's up to the discovery of the Higgs boson. It is mainly meant for students at master level, and at some points it is presented somewhat different from standard textbook presentations.

hep-ph↗
arXiv2020

Electric dipole moment of the neutron in Two Higgs Doublet Models with flavor changing

I consider contributions to the neutron electric dipole moment within Two Higgs Doublet Models which allow for small flavor changing neutral Higgs couplings. In a previous paper, I considered flavor changing interactions for the Standard Model Higgs boson to first order in the flavor changing coupling. In that paper I found that the obtained value of the neutron electric dipole moment were below the present experimental limit, given previous restrictions on such couplings. Because this was an effective theory, the result depended on an ultraviolet cut off $Λ$, parametrized as $ln(Λ^2)$. In the present paper I demonstrate that, when going to Two Higgs Doublet Models, the result stays the same as in the previous paper, up to $M_{SM}^2/M_H^2$ corrections, where $M_{SM}$ is the mass of the top-quark or the $W$-boson. $M_H$ is the mass of the heavy neutral scalar Higgs-boson $H$ which is much heavier than the light neutral Higgs boson $h$ with mass $M_h$. In the limit $M_H^2 \gg M_h^2$, the $ln(Λ^2)$ behaviour in the previous paper is replaced by $ln(\widetilde{M_H}^2)$, where $\widetilde{M_H}$ is of order $M_H$. I also explain how some divergences due to exchange of the pseudoscalar Higgs $A$ are cancelled by similar contributions from the scalar heavy Higgs $H$, and that these contributions, and finite contributions from $A$-exchange, are suppressed.

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arXiv2018

Electric dipole moment of the neutron from a flavor changing Higgs boson

I consider neutron electric dipole moment contributions induced by flavor changing Standard Model Higgs boson couplings to quarks. Such couplings might stem from non-renormalizable $SU(2)_L \times U(1)_Y$ invariant Lagrange terms of dimension six, containing a product of three Higgs doublets. Previously one loop diagrams with such couplings were considered in order to constrain {\it quadratric} expressions of Higgs flavor changing couplings to quarks. In the present paper the analysis is extended to the two loop level, where there are diagrams for electric dipole moments of quarks with a flavor changing Higgs coupling to {\it first order only}. The divergent loops, due to non-renormalisabillity, are parametrized in terms of an ultraviolet cut-off $Λ$. I also consider QCD corrections, including the mixing with the color electric dipole moment, while the contribution from the Weinberg operator is found to be negligible. The effect of QCD corrections is to suppress the bare result. Using the current experimental bound on the neutron electric dipole moment, then for cut offs from one to seven TeV, I find a constraint of order $10^{-3}$ for the imaginary part of the {\it product} of the Higgs flavor changing coupling for $(d \rightarrow b)$-transition {\it and} the CKM element $V_{td}$. Assuming that the previous bound of the {\it absolute value} of the Higgs flavor changing coupling for $(d \rightarrow b)$-transition obtained from $B_d - \bar{B_d}$-mixing is saturated, the experimental bound on the neutron electric dipole moment would be reached for the {\it bare} result, {\it if} the cut off were extended up to about ca 20 TeV. However, QCD corrections suppress this result by a factor of order ten, and keep the nEDM below the experimental bound.

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arXiv2016

New physics in ε' from chromomagnetic contributions and limits on Left-Right symmetry

New physics in the chromomagnetic flavor changing transition s->dg* can avoid the strong GIM suppression of the Standard Model and lead to large contributions to CP-violating observables, in particular to the epsilon' parameter, that we address here. We discuss the case of the Left-Right symmetric models, where this contribution implies bounds on the phases of the right-handed quark mixing matrix, or in generic models with large phases a strong bound on the Left-Right symmetry scale. To the leading order, a numeric formula for epsilon' as a function of the short-distance coefficients for a wide class of models of new physics is given.

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arXiv2014

Colored scalars and the neutron electric dipole moment

We investigate new contributions to the neutron electric dipole moment induced by colored scalars. As an example, we evaluate contributions coming from the color octet, weak doublet scalar, accommodated within a modified Minimal Flavor Violating framework. These flavor non-diagonal couplings of the color octet scalar might account for the $A_{CP} (D^0 \to K^- K^+) - A_{CP} (D^0 \to π^+ π^-)$ asymmetry on the tree level. Using these charm asymmetry constrained couplings, we calculate two-loop contributions to the neutron electric dipole moment and find that they are of the same order as the experimental bound. We comment also on contributions of higher dimensional operators to the neutron electric dipole moment within this framework.

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arXiv2013

Form factors for semileptonic D decays

We study the form factors for semileptonic decays of $D$-mesons. That is, we consider the matrix element of the weak left-handed quark current for the transitions $D \rightarrow P$ and $D \rightarrow V$, where $P$ and $V$ are light pseudoscalar or vector mesons, respectively. Our motivation to perform the present study of these form factors are future calculations of non-leptonic decay amplitudes. We consider the form factors within a class of chiral quark models. Especially, we study how the Large Energy Effective Theory (LEET) limit works for $D$-meson decays. Compared to previous work we also introduce light vector mesons $V = ρ, K^*,...$ within chiral quark models. In order to determine some of the parameters in our model, we use existing data and results based on some other methods like lattice calculations, light-cone sum rules, and heavy-light chiral perturbation theory. We also obtain some predictions within our framework.

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arXiv2010

On the color suppressed contribution to $\bar{B_{d}^0} \rightarrow \, π^0 π^{0}

The decay modes of the type $B \rightarrow π\, π$ are dynamically different. For the case $\bar{B_{d}^0} \rightarrow \, π^+ π^- $ there is a substantial factorized contribution which dominates. In contrast, the decay mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ has a small factorized contribution, being proportional to a small Wilson coefficient combination. However, for the decay mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ there is a sizeable nonfactorizable (color suppressed) contribution due to soft (long distance) interactions, which dominate the amplitude. We estimate the branching ratio for the mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ in the heavy quark limit for the $b$- quark. In order to estimate color suppressed contributions we treat the energetic light ($u,d,s$) quark within a variant of Large Energy Effective Theory combined with a recent extension of chiral quark models in terms of model- dependent gluon condensates. We find that our calculated color suppressed amplitude is suppressed by a factor of order $Λ_{QCD}/m_b$ with respect to the factorizable amplitude, as it should according to QCD-factorization. Further, for reasonable values of the constituent quark mass and the gluon condensate, 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} $. A possible link to the triangle anomaly is discussed.

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arXiv2010

Non-factorizable contribtion to $\bar{B_{d}^0} \to π^0 D^{0}$

The decay modes of the type $B \to π\, D $ are dynamically different. For the case $\bar{B_{d}^0} \to π^- D^{+} $ there is a substantial factorized contribution which dominates. In contrast, the decay mode $\bar{B_{d}^0} \to π^0 D^{0} $ has a small factorized contribution, being proportional to a very small Wilson coefficient combination. In this paper we calculate the relevant Wilson coefficients at one loop level in the heavy quark limits, both for the $b$-quark and the $c$-quark. We also emphasize that for the decay mode $\bar{B_{d}^0} \to π^0 D^{0}$ there is a sizeable non-factorizable contribution due long distance interactions, which dominate the amplitude. We estimate the branching ratio for this decay mode within our framework, which uses the heavy quark limits, both for the $b$- and the $c$-quarks. In addition, we treat energetic light ($u,d,s$) quarks within a variant of Large Energy Effective Theory and combine this with a new extension of chiral quark models. For reasonable values of the model dependent parameters of our model can account for at least 3/4 of the amplitude needed to explain the experimental branching ratio $\simeq 2.6 \times 10^{-4}$.

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arXiv2009

The Isgur-Wise Function within a Modified Heavy-Light Chiral Quark Model

We consider the Isgur-Wise function xi(omega) within a new modified version of a heavy-light chiral quark model. While early versions of such models gave too small absolute value of the slope, namely xi'(1) of about -0.4 to -0.3, we show how extended version(s) may lead to values around -1, in better agreement with recent measurements. This is obtained by introducing a new mass parameter in the heavy quark propagator. We also shortly comment on the consequences for the decay modes B --> D D-bar.

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arXiv2008

New Dipole Penguin Contribution to K --> pi pi decays

We point out that the standard chromomagnetic penguin dipole operator has a counterpart corresponding to off-shell momenta for external quarks. By employing the chiral quark model, we show that this new dipole penguin operator has the same bosonisation as the standard Q_6 operator. Accordingly, this new operator enlarges by ~ 5 % the referent Q_6 contribution, which gives the dominant contribution to the CP-violating ratio epsilon'/epsilon and also gives an important contribution to the Delta I = 1/2 amplitude.

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arXiv2008

Chiral loop corrections in B to D l nu decays

We determine chiral loop corrections to the B meson decay amplitudes to positive and negative parity charmed mesons within a framework which combines heavy quark and chiral symmetries. We find that corrections due to states of opposite parity are competitive with the contributions arising from K and eta meson loops. Since lattice studies rely on the chiral behavior of the amplitudes we discuss the chiral limit of our results. We also comment on the extraction of 1/m_B, 1/m_D subleading form factors relevant for the studies of B_q to D_q tau nu decays, which are sensitive to possible helicity-suppressed new physics contributions.

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arXiv2008

Chiral corrections to the scalar form factor in B_q to D_q transitions

We consider chiral loop corrections to the scalar form factor in B_q to D_q l nu decays. First we consider chiral corrections to the 1/m_Q suppressed operators and then we propose the procedure for the extraction of the relevant form factor using lattice QCD results. In the case of B_s to D_s l nu decay we find that effects of kinematics and chiral corrections tend to cancel for the scalar form factor contributions. In particular the 1/m_Q suppression of chiral corrections is compensated by the SU(3) flavor symmetry breaking corrections which can be as large as 30%. The calculated corrections are relevant for the precise determination of possible new physics effects in B_q to D_q l nu decays.

hep-ph↗
arXiv2007

Chiral loop corrections to weak decays of B mesons to positive and negative parity charmed mesons

We determine chiral loop corrections to the B meson decay amplitudes to positive and negative parity charmed mesons within a framework which combines heavy quark and chiral symmetries. Then we investigate the impact of the lowest-lying positive parity heavy mesons on the determination of the Isgur-Wise functions. The corrections due to these states are competitive with the contributions arising from K and eta meson loops. Since lattice studies rely on the chiral behavior of the amplitudes we discuss the chiral limit of our results. We find that the determination of the slope at zero recoil of the Isgur-Wise function xi for the B transition to negative parity charm mesons is moderately affected by the inclusion of new states, while the slope of tau_{1/2} is affected significantly more.

hep-ph↗
arXiv2007

Low Energy Aspects of Heavy Meson Decays

I discuss low energy aspects of heavy meson decays, where there is at least one heavy meson in the final state. Examples are $B -\bar{B}$ mixing, $B \to D \bar{D}$, $B \to D η'$, and $B \to D γ$. %and $B \to D W $ (Isgur-Wise function). The analysis is performed in the heavy quark limit within heavy-light chiral perturbation theory. Coefficients of $1/N_c$ suppressed chiral Lagrangian terms (beyond factorization) have been estimated by means of a heavy-light chiral quark model.

hep-ph↗
arXiv2005

Color suppressed contributions to the decay modes B_{d,s} -> D_{s,d} D_{s,d}, B_{d,s} -> D_{s,d} D^*_{s,d}, and B_{d,s} -> D^*_{s,d} D^*_{s,d}

The amplitudes for decays of the type $B_{d,s} \to D_{s,d} D_{s,d}$, have no factorizable contributions, while $B_{d,s} \to D_{s,d} D^*_{s,d}$, and $B_{d,s} \to D^*_{s,d} D^*_{s,d}$ have relatively small factorizable contributions through the annihilation mechanism. The dominant contributions to the decay amplitudes arise from chiral loop contributions and tree level amplitudes which can be obtained in terms of soft gluon emissions forming a gluon condensate. 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 $(4- 7) \times 10^{-3}$. We obtain branching ratios for two $D^*$'s in the final state of order two times bigger.

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arXiv2004

Chiral quark models and their applications

We give an overview of chiral quark models, both for the pure light sector and the heavy-light sector. We describe how such models can be bosonized to obtain welWe give an overview of chiral quark models, both for the pure light sector and the heavy-light sector. We describe how such models can be bosonized to obtain well known chiral Lagrangians which can be inferred from the symmetries of QCD alone. In addition, we can within these models calculate the coefficients of the various pieces of the chiral Lagrangians. We discuss a few applications of the models, in particular, $\bbar$ mixing and processes of the type $B \to D \bar{D}$, where $D$ might be both pseudoscalar and vector. We suggest how the formalism might be extended to include light vectors ($ρ,ω,K^*$), and heavy to light transitions like $B \to π$. l known chiral Lagrangians which can be inferred from the symmetries of QCD alone. In addition, we can within these models calculate the coefficients of the various pieces of the chiral Lagrangians. We discuss a few applications of the models, in particular, $\bbar$ mixing and processes of the type $B \to D \bar{D}$, where $D$ might be both pseudoscalar and vector. We suggest how the formalism might be extended to include light vectors ($ρ,ω,K^*$), and heavy to light transitions like $B \to π$.

hep-ph↗
arXiv2000

An updated analysis of eps'/eps in the standard model with hadronic matrix elements from the chiral quark model

We discuss the theoretical and experimental status of the CP violating ratio eps'/eps. We revise our 1997 standard-model estimate-based on hadronic matrix elements computed in the chiral quark model up to O(p^4) in the chiral expansion-by including an improved statistical analysis of the uncertainties and updated determination of the Cabibbo-Kobayashi-Maskawa elements and other short-distance parameters. Using normal distributions for the experimental input data we find Re eps'/eps = (2.2 \pm 0.8) x 10^{-3}, whereas a flat scanning gives 0.9 x 10^{-3} < Re eps'/eps < 4.8 x 10^{-3}. Both results are in agreement with the current experimental data. The key element in our estimate is, as before, the fit of the Delta I=1/2 rule, which allows us to absorb most of the theoretical uncertainties in the determination of the model-dependent parameters in the hadronic matrix elements. Our semi-phenomenological approach leads to numerical stability against variations of the renormalization scale and scheme dependence of the short- and long-distance components. The same dynamical mechanism at work in the selection rule also explains the larger value obtained for \ratio with respect to other estimates. A coherent picture of K -> pi pi decays is thus provided.

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