arXiv subjects

Martin Jung

Publications and source records attributed to Martin Jung.

53 records · Page 3Linked to original sources

arXiv2014

Electric Dipole Moments in Two-Higgs-Doublet Models

Electric dipole moments are extremely sensitive probes for additional sources of CP violation in new physics models. Specifically, they have been argued in the past to exclude new CP-violating phases in two-Higgs-doublet models. Since recently models including such phases have been discussed widely, we revisit the available constraints in the presence of mechanisms which are typically invoked to evade flavour-changing neutral currents. To that aim, we start by assessing the necessary calculations on the hadronic, nuclear and atomic/molecular level, deriving expressions with conservative error estimates. Their phenomenological analysis in the context of two-Higgs-doublet models yields strong constraints, in some cases weakened by a cancellation mechanism among contributions from neutral scalars. While the corresponding parameter combinations do not yet have to be unnaturally small, the constraints are likely to preclude large effects in other CP-violating observables. Nevertheless, the generically expected contributions to electric dipole moments in this class of models lie within the projected sensitivity of the next-generation experiments.

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arXiv2013

SU(3)F in nonleptonic charm decays

We present updated results of an SU(3)-flavor analysis of D->P P decay data including linear breaking and no further assumptions. The global fit is consistent with nominal (~ 30%) SU(3)F breaking and returns enhanced penguin (triplet) contributions. Their size is driven, in addition to Delta A_{CP}, by the CP asymmetries of D_0->K_S K_S, D_s->K_S pi^+ and D_s->K^+ pi^0 decays. It is therefore especially important to improve these measurements.

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arXiv2013

B -> D(*) Tau Nu decays in two-Higgs-doublet models

A sizable excess with respect to the SM expectation has been reported recently by the BaBar collaboration in the decay rates B -> D(*) Tau Nu, normalized by the corresponding light lepton modes. A violation of lepton flavor universality as suggested by this excess could be due to a charged Higgs mediating these processes at tree level. In this talk we analyze the implications of the observed excess within the framework of two-Higgs-doublet models, considering also the bounds from other semileptonic and leptonic decays of B and D(s) mesons. Prospects for B -> D(*) Tau Nu decays at future Super-Flavor Factories are also discussed.

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arXiv2013

SU(3)-Flavor Anatomy of Non-Leptonic Charm Decays

We perform a comprehensive SU(3)-flavor analysis of charmed mesons decaying to two pseudoscalar SU(3)-octet mesons. Taking into account SU(3)-breaking effects induced by the splitting of the quark masses, m_s != m_{u,d}, we find that existing data can be described by SU(3)-breaking of the order 30%. The requisite penguin enhancement to accomodate all data on CP violation tends to be even larger than the one extracted from Delta a_{CP}^{dir}(K^+K^-,pi^+pi^-) alone, strengthening explanations beyond the standard model. Despite the large number of matrix elements, correlations between CP asymmetries allow potentially to differentiate between different scenarios for the underlying dynamics, as well as between the standard model and various extensions characterized by SU(3) symmetry and its subgroups. We investigate how improved measurements of the direct CP asymmetries in singly-Cabibbo-suppressed decays can further substantiate the interpretation of the data. We show that particularly informative are the asymmetries in D->pi^+pi^- versus D->K^+K^-, D_s->K_S pi^+ versus D^+->K_S K^+, D^+->pi^+ pi^0, D->pi^0pi^0, and D->K_S K_S.

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arXiv2013

A robust limit for the electric dipole moment of the electron

Electric dipole moments constitute a competitive method to search for new physics, being particularly sensitive to new CP-violating phases. Given the experimental and theoretical progress in this field and more generally in particle physics, the necessity for more reliable bounds than the ones usually employed emerges. We therefore propose an improved extraction of the electric dipole moment of the electron and the relevant coefficient of the electron-nucleon coupling, taking into account theoretical uncertainties and possible cancellations, to be used in model-dependent analyses. Specifically, we obtain at 95% C.L. |d_e|<=0.14 10^{-26}e cm with present data, which is very similar to the bound typically quoted from the YbF molecule, but obtained in a more conservative manner. We examine furthermore in detail the prospects for improvements and derive upper limits for the dipole moments of several paramagnetic systems presently under investigation, i.e. Cesium, Rubidium and Francium.

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arXiv2013

Sensitivity to charged scalars in $B\to D^{(*)}τν_τ$ and $B\toτν_τ$ decays

We analyze the recent experimental evidence for an excess of $τ$-lepton production in several exclusive semileptonic $B$-meson decays in the context of two-Higgs-doublet models. These decay modes are sensitive to the exchange of charged scalars and constrain strongly their Yukawa interactions. While the usual Type-II scenario cannot accommodate the recent BaBar data, this is possible within more general models in which the charged-scalar couplings to up-type quarks are not as suppressed. Both the $B\to D^{(*)}τν_τ$ and the $B\toτν_τ$ data can be fitted within the framework of the Aligned Two-Higgs-Doublet Model, but the resulting parameter ranges are in conflict with the constraints from leptonic charm decays. This could indicate a departure from the family universality of the Yukawa couplings, beyond their characteristic fermion mass dependence. We discuss several new observables that are sensitive to a hypothetical charged-scalar contribution, demonstrating that they are well suited to distinguish between different scenarios of new physics in the scalar sector, and also between this group and models with different Dirac structures; their experimental study would therefore shed light on the relevance of scalar exchanges in semileptonic $b\to c\,τ^-\barν_τ$ transitions.

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arXiv2012

Penguin contributions to B to J/Psi P Decays

The high precision to which the standard model has been confirmed implies that new physics effects have to be small in the observed processes. Together with the outstanding precision expected from present and future collider experiments this renders the evaluation of subleading SM contributions necessary. For the "golden mode", B_d to J/Psi K, these so-called "penguin pollution" terms can be controlled by using flavour symmetry relations. A recent analysis is presented which yields a stronger bound on the maximal penguin influence than previous ones and shows how the corresponding uncertainty can be reduced with coming data.

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arXiv2012

Recent topics in CP violation

Recent topics regarding CP violation in heavy meson systems are discussed. As an introduction, the status of the Unitarity Triangle fit and CP violation in B meson mixing are briefly reviewed. Two topics are covered in more detail: Penguin pollution in the "golden mode" B_d to J/psi K has gained importance due to the apparent smallness of new physics effects, together with the outstanding precision expected from present and future collider experiments. A very recent analysis is presented, which yields a stronger bound for the maximal influence of penguin contributions than previous analyses and shows the corresponding uncertainty to be reducible with coming data. Direct CP violation in hadronic charm decays received a lot of attention lately, due to a measurement by the LHCb collaboration yielding an unexpectedly large result. While this value is certainly not generically predicted in the Standard Model, it might be possible to accommodate it nevertheless. Therefore a method is discussed to use flavour symmetries to distinguish between this possibility and new physics.

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arXiv2012

Exclusive radiative B-meson decays within the aligned two-Higgs-doublet model

In the aligned two-Higgs-doublet model, the alignment of Yukawa matrices in flavour space guarantees the absence of tree-level flavour-changing neutral currents, while allowing at the same time for new sources of CP violation, implying potentially large effects in many low-energy processes. In this work we study the constraints from exclusive radiative $B\to Vγ$ decays, where $V$ denotes a light vector meson. The current experimental data on the CP-averaged branching ratios and the direct CP and isospin asymmetries are analyzed. It is found that, while the branching ratios and direct CP asymmetries do not constrain the parameter space much further compared to the inclusive $B\to X_{s,d} γ$ decays, complementary constraints can be obtained from the isospin asymmetries $Δ(K^*γ)$ and $Δ(ργ)$. In addition, correlations between the various observables in exclusive $B\to Vγ$ and inclusive $B\to X_{s,d} γ$ decays are investigated in detail, and predictions are made for several so far unmeasured observables.

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arXiv2012

Determining weak phases from B->J/Psi P decays

The decay B -> J/Psi K_S remains the most important source of information for the B_d mixing phase, determined by the CKM angle beta in the standard model. When aiming at a precision appropriate for present and coming high luminosity colliders, the corresponding hadronic matrix elements are a major obstacle, as their precise calculation is still not feasible with existing methods. Flavour symmetries offer a possibility to extract them from data, however again with limited precision. In this article, we propose a framework to take subleading contributions in B_{u,d,s} -> J/Psi P decays into account, P=(pi,K,(eta_8)), using an SU(3) analysis, together with the leading corrections to the symmetry limit. This allows for a model-independent extraction of the B_d mixing phase adequate for coming high precision data, and additionally yields information on possible New Physics contributions in these modes. We find the penguin-induced correction to be small, |Delta S|<~0.01, a limit which can be improved with coming data on CP asymmetries and branching ratios. Finally, the sensitivity on the CKM angle gamma from these modes is critically examined, yielding a less optimistic picture than previously envisaged.

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arXiv2010

Flavour Physics in two-Higgs-doublet models

Despite the tremendous success of the Standard Model, the arguments for the necessity of an extension are compelling. An attractive option is provided by Two-Higgs-Doublet models, due to their simplicity and them being the low-energy limit of some more complete theories. In the most general version of the model, the fermionic couplings of the neutral scalars are non-diagonal in flavour and, therefore, generate unwanted flavour-changing neutral-current phenomena. Different ways to suppress FCNCs have been developed, giving rise to a variety of specific implementations of the 2HDM. Three of these are discussed in this talk, comparing their phenomenological influence in flavour observables: The use of a discrete Z2-symmetry, an expansion around this limit in a minimal flavour violation scenario assuming the decoupling limit, and the Aligned Two-Higgs-Doublet Model. All of these result in the absence of tree-level flavour-changing neutral currents. Their different phenomenological consequences are demonstrated for a selection of observables, namely (semi-) leptonic decays, B->X_s gamma and mixing in the B0_d,s-systems.

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arXiv2010

The B -> Xs gamma Rate and CP Asymmetry within the Aligned Two-Higgs-Doublet Model

In the two-Higgs-doublet model the alignment of the Yukawa matrices in flavour space guarantees the absence of flavour-changing neutral currents at tree level, while introducing new sources for CP violation parametrized in a very economical way. This implies potentially large influence in a number of processes, b -> s gamma being a prominent example where rather high experimental and theoretical precision meet. We analyze the CP rate asymmetry in this inclusive decay and determine the resulting constraints on the model parameters. We demonstrate the compatibility with previously obtained limits. Moreover we extend the phenomenological analysis of the branching ratio, and examine the influence of resulting correlations on the like-sign dimuon charge asymmetry in B decays.

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arXiv2010

Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model

The alignment in flavour space of the Yukawa matrices of a general two-Higgs-doublet model results in the absence of tree-level flavour-changing neutral currents. In addition to the usual fermion masses and mixings, the aligned Yukawa structure only contains three complex parameters, which are potential new sources of CP violation. For particular values of these three parameters all known specific implementations of the model based on discrete Z_2 symmetries are recovered. One of the most distinctive features of the two-Higgs-doublet model is the presence of a charged scalar. In this work, we discuss its main phenomenological consequences in flavour-changing processes at low energies and derive the corresponding constraints on the parameters of the aligned two-Higgs-doublet model.

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arXiv2009

General Analysis of U-Spin Breaking in B Decays

We analyse the breaking of U-spin on a group theoretical basis. Due to the simple behaviour of the weak effective hamiltonian under U-spin and the unique structure of the breaking terms such a group theoretical analysis leads to a manageable number of parameters. Several applications are discussed, including the decays B -> J/psi K and B -> D K.

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arXiv2009

Is there a non-standard-model contribution in non-leptonic b to s decays?

The data on high-precision flavour observables reveal certain puzzles when compared to Standard Model expectations based on a global fit of the CKM unitarity triangle and general theoretical estimates. The discussion of these tensions in the channels B to J/psi K, B to phi K, and B to pi K, and the deduced constraints for New Physics operators of the class (bs)(qq) form the content of this talk.

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arXiv2008

Is there a non-Standard-Model contribution in non-leptonic b -> s decays?

Precision measurements of branching fractions and CP asymmetries in non-leptonic b -> s decays reveal certain "puzzles" when compared with Standard Model expectations based on a global fit of the CKM triangle and general theoretical expectations. Without reference to a particular model, we investigate to what extent the (small) discrepancies observed in (B -> J/psi K), (B -> phi K) and (B -> K pi) may constrain new physics in (b -> s q qbar) operators. In particular, we compare on a quantitative level the relative impact of different quark flavours q=c,s,u,d.

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arXiv2008

The Golden Modes B^0 -> J/psi K_{S,L} in the Era of Precision Flavour Physics

The B^0 -> J/ψK_{S,L} channels are outstanding probes of CP violation. We have a detailed look at the associated Standard-Model uncertainties, which are related to doubly Cabibbo-suppressed penguin contributions, and point out that these usually neglected effects can actually be taken into account unambiguously through the CP asymmetries and the branching ratio of the B^0 -> J/ψpi^0 decay. Using the most recent B-factory measurements, we find a negative shift of the extracted value of beta, which softens the tension in the fits of the unitarity triangle. In addition, this strategy can be used to constrain a possible new-physics phase in B^0-\bar B^0 mixing. The proposed strategy is crucial to fully exploit the tremendous accuracies for the search for this kind of new physics that can be achieved at the LHC and future super-flavour factories.

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