arXiv subjects

Andrzej J. Buras

Publications and source records attributed to Andrzej J. Buras.

At least 91 records · Page 5Linked to original sources

arXiv2014

Z-Z' Mixing and Z-Mediated FCNCs in SU(3)_C x SU(3)_L x U(1)_X Models

Most of the existing analyses of FCNC processes in the 331 models, based on the gauge group SU(3)_C x SU(3)_L x U(1)_X, take only into account tree-level exchanges of a new heavy neutral gauge boson Z'. However due to the Z-Z' mixing also corresponding contributions from Z boson are present that are usually neglected. We calculate the impact of these contributions on Delta F=2 processes and rare K, B_s and B_d decays for different values of a parameter beta, which distinguishes between various 331 models and for different fermion representations under the SU(3)_L group. We find a general expression for the Z-Z' mixing in terms beta, M_Z, M_Z' and tan(bar{beta}), familiar from 2 Higgs Doublet models, that differs from the one quoted in the literature. We study in particular the models with beta=+-n/sqrt{3} with n=1,2 which have recently been investigated by us in the context of new data on B_{s,d}->mu^+ mu^- and B_d->K^*(K)mu^+ mu^-. We find that these new contributions can indeed be neglected in the case of Delta F=2 transitions and decays, like B_d->K^*mu^+mu^-, where they are suppressed by the small vectorial Z coupling to charged leptons. However the contributions of tree-level Z exchanges to decays sensitive to axial-vector couplings, like B_{s,d}->mu^+ mu^- and B_d->K mu^+ mu^-, and those with neutrinos in the final state, like b->s nu bar{nu} transitions, K^+->pi^+ nu bar{nu} and K_L->pi^0 nu bar{nu} cannot be generally neglected with size of Z contributions depending on beta, tan(bar{beta}) and M_Z'. We analyze for the first time the ratio epsilon'/epsilon in these models including both Z' and Z contributions. Our analysis of electroweak precision observables within 331 models demonstrates transparently that the interplay of NP effects in electroweak precision observables and those in flavour observables could allow in the future to identify the favourite 331 model.

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arXiv2014

Delta I=1/2 Rule, epsilon'/epsilon and K -> pi nu nubar in Z'(Z) and G' Models with FCNC Quark Couplings

The experimental value for the isospin amplitude Re(A_2) in K->pi pi decays has been successfully explained within the Standard Model, both within large N approach to QCD and by QCD lattice calculations. On the other hand in both approaches the theoretical values of Re(A_0) are by at least 30% below the data so that the Delta I=1/2 rule in K->pi pi decays is not fully explained. While this deficit could be the result of present theoretical uncertainties in both approaches, it cannot be excluded that the missing piece in Re(A_0) comes from New Physics. We demonstrate that this deficit can be significantly softened by tree-level FCNC transitions mediated by a heavy colourless Z' gauge boson with particularly chosen flavour violating couplings assuring negligible NP contributions to Re(A_2) and significantly enhancing the contribution of the leading QCD penguin operator Q_6 to Re(A_0). A large fraction of the missing piece in the Delta I=1/2 rule can be explained in this manner for M_{Z'} in the reach of the LHC, while satisfying constraints from epsilon_K, epsilon'/epsilon, Delta M_K, LEP-II and the LHC. We identify quartic correlation between Z' contributions to Re(A_0), epsilon'/epsilon, epsilon_K and Delta M_K. We present correlations between epsilon'/epsilon and rare decays K->pi nu bar{nu} with and without the Delta I=1/2 rule constraint and generalize the whole analysis to Z' with colour (G') and Z with FCNC couplings. In the latter case no improvement on Re(A_0) can be achieved without destroying the agreement of the SM with the data on Re(A_2). Moreover, this scenario is very tightly constrained by epsilon'/epsilon. On the other hand in the context of the Delta I=1/2 rule G' is even more effective than Z': it provides the missing piece in Re(A_0) for M_{G'}=(3.5-4.0) TeV.

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arXiv2014

Towards the Identification of New Physics through Quark Flavour Violating Processes

We outline a systematic strategy which should help in this decade to identify New Physics beyond the Standard Model by means of quark flavour violating processes and thereby to extend the picture of short distance physics down to the scales as short as 10^{-20} m and even shorter distance scales corresponding to energies of 100 TeV. Rather then using all possible flavour violating observables that will be measured in the coming years, we concentrate on those observables that are theoretically clean and very sensitive to NP. Assuming that the data on the selected observables by us will be very precise, we stress the importance of correlations between these observables as well as of future precise calculations of non-perturbative parameters by means of lattice QCD. Our strategy consists of twelve steps which we will discuss in detail illustrating possible outcomes with the help of the SM, models with CMFV, MFV and models with tree-level FCNCs mediated by neutral gauge bosons and scalars. We propose DNA-charts that exhibit correlations between flavour observables in different NP scenarios. The models with new left-handed and/or right-handed currents and non-MFV interactions can be distinguished transparently in this manner. We emphasis the important role of the stringent CMFV relations between various observables as standard candles of flavour physics. The pattern of deviations from these relations may help in identifying the correct NP scenario. The success of this program will be very much facilitated through direct signals of NP at the LHC. We also emphasize the importance of lepton flavour violation, electric dipole moments and (g-2)_{e,mu} in these studies.

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arXiv2014

Large N Approach to Kaon Decays and Mixing 28 Years Later: Delta I = 1/2 Rule, \hat B_K and Delta M_K

We review and update our results for K-> pipi decays and K^0-\bar K^0 mixing obtained by us in the 1980s within an approach based on the dual representation of QCD as a theory of weakly interacting mesons for large N colours. In our analytic approach the dynamics behind the enhancement of ReA_0 and suppression of ReA_2, the so-called Delta I = 1/2 rule for K-> pi pi decays, has a simple structure: the usual octet enhancement through quark-gluon renormalization group evolution down to the scales O(1 GeV) is continued as a meson evolution down to zero momentum scales at which the factorization of hadronic matrix elements is at work. The inclusion of lowest-lying vector meson contributions in addition to the pseudoscalar ones and of Wilson coefficients in a momentum scheme improves significantly the matching between quark-gluon and meson evolutions. In particular, the anomalous dimension matrix governing the meson evolution exhibits the structure of the known anomalous dimension matrix in the quark-gluon evolution. The recent results on ReA_2 and ReA_0 from the RBC-UKQC collaboration give support for our approach. In particular, the signs of the two main contractions found numerically by these authors follow uniquely from our analytic approach. At NLO in 1/N we obtain ReA_0/ReA_2= 16.0\pm 1.5 which amounts to an order of magnitude enhancement over the strict large N limit value sqrt{2}. QCD penguins contribute at 15% level to this result. We also find \hat B_K=0.73\pm 0.02, with the smallness of 1/N corrections to the large N value \hat B_K=3/4 resulting within our approach from an approximate cancellation between pseudoscalar and vector meson one-loop contributions. We summarize the status of Delta M_K in this approach.

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arXiv2013

331 models facing new b -> s mu^+ mu^- data

We investigate how the 331 models face new data on B_{s,d}->mu^+mu^- and B_d->K^*mu^+mu^- taking into account present constraints from Delta F=2 observables, low energy precision measurements, LEP-II and the LHC data. In these models new flavour violating interactions of ordinary quarks and leptons are dominated by a new heavy Z^prime gauge boson with the strength of the relevant couplings governed by four new parameters in the quark sector and the parameter beta. We study the implications of these models for beta=+-n/sqrt{3} with n=1,2,3. The case beta=-sqrt{3} leading to Landau singularities for M_{Z'}approx 4Tev can be ruled out when the present constraints on Z^prime couplings, in particular from LEP-II, are taken into account. For n=1,2 interesting results are found for M_{Z^prime}< 4Tev with largest NP effects for beta<0 in B_d->K^*mu^+mu^- and the ones in B_{s,d}->mu^+mu^- for beta>0. As Re(C_9^NP) can reach the values -0.8 and -0.4 for n=2 and n=1, respectively the B_d-> K^*mu^+mu^- anomalies can be softened with the size depending on Delta M_s/(Delta M_s)_SM and the CP-asymmetry S_{psiphi}. A correlation between Re(C_9^NP) and BR(B_s->mu^+mu^-), identified for beta<0, implies for negative Re(C_9^NP) uniquely suppression of BR(B_s->mu^+mu^-) relative to its SM value which is favoured by the data. In turn also S_{psiphi}< S_{psiphi}^SM is favoured having dominantly opposite sign to S_{psiphi}^SM. We find that the absence of B_d-> K^*mu^+mu^- anomalies in the future data and confirmation of the suppression of BR(B_s->mu^+mu^-) relative to its SM value would favour beta=1/sqrt{3} and M_{Z'}approx 3Tev. Assuming lepton universality, we find an upper bound |C_9^NP|<1.1(1.4) from LEP-II data for all Z' models with only left-handed flavour violating couplings to quarks when NP contributions to Delta M_s at the level of 10%(15%) are allowed.

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arXiv2013

Left-handed Z' and Z FCNC quark couplings facing new b -> s mu^+ mu^- data

In view of the recent improved data on B_{s,d}->mu^+ mu^- and B_d->K^*mu^+mu^- we revisit two simple NP scenarios in which new FCNC currents in b->s mu^+ mu^- transitions are mediated either entirely by a neutral heavy gauge boson Z' with purely LH complex couplings Delta_L^{qb}(Z') (q=d,s) and couplings to muons Delta_A^{mu mu}(Z') and Delta_V^{mu mu}(Z') or the SM Z boson with LH complex couplings Delta_L^{qb}(Z). We demonstrate how these couplings can be determined by future Delta F=2 and b->s mu^+ mu^- observables. The correlations between various observables can test these NP scenarios. We present the results as functions of Delta M_q/Delta M_q^SM, S_{psi phi} and S_{psi K_S} which should be precisely determined in this decade. We calculate the violation of the CMFV relation between BR(B_{s,d}-> mu^+ mu^-) and Delta M_{s,d} in these scenarios. We find that the data on B_{s,d}->mu^+ mu^- from CMS and LHCb can be reproduced in both scenarios but in the case of Z, Delta M_s and S_{psi phi} have to be very close to their SM values. As far as B_d->K^*mu^+mu^- anomalies are concerned the Z' scenario can significantly soften these anomalies while the Z boson fails because of the small vector coupling to muons. We also point out that recent proposals of explaining these anomalies with the help of a real Wilson coefficient C^NP_9 implies uniquely an enhancement of Delta M_s with respect to its SM value, while a complex C^NP_9 allows for both enhancement and suppression of Delta M_s and simultaneously novel CP-violating effects. We also discuss briefly scenarios in which the Z' boson has RH FCNC couplings. In this context we point out a number of correlations between angular observables measured in B_d->K^*mu^+ mu^- that arise in the absence of new CP-violating phases in scenarios with only LH or RH couplings or scenarios in which LH and RH couplings are equal to each other or differ by sign.

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arXiv2013

Towards the Identification of New Physics through Correlations between Flavour Observables

We emphasize the power of correlations between flavour observables in the search for New Physics and identify a number of correlations that could allow to discover New Physics even if it would appear at the level of 20% of the Standard Model contributions. After presenting the simplest correlations in CMFV and U(2)^3 models we address the recent data on B_{s,d}->mu^+ mu^- and the anomalies in B_d -> K^* mu^+ mu^- in the context of Z'-models and SM Z, both with flavour violating neutral couplings. A strategy consisting of twelve steps which concentrate on theoretically clean observables, to be measured in this decade, could one day allow us to reach the Zeptouniverse. The related DNA charts based on the correlations between enhancements and supressions of various observables in a given New Physics scenario relative to the Standard Model predictions allow a transparent distinction between various extensions of this model. The present text is the extended version of the talk to be published in the proceedings of this symposium.

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arXiv2013

Probing New Physics with the B_s to μ+ μ- Time-Dependent Rate

The B_s to mu+ mu- decay plays an outstanding role in tests of the Standard Model and physics beyond it. The LHCb collaboration has recently reported the first evidence for this decay at the 3.5 sigma level, with a branching ratio in the ballpark of the Standard Model prediction. Thanks to the recently established sizable decay width difference of the B_s system, another observable, A^mumu_DeltaGamma, is available, which can be extracted from the time-dependent untagged B_s to mu+ mu- rate. If tagging information is available, a CP-violating asymmetry, S_mumu, can also be determined. These two observables exhibit sensitivity to New Physics that is complementary to the branching ratio. We define and analyse scenarios in which these quantities allow us to discriminate between model-independent effective operators and their CP-violating phases. In this context we classify a selection of popular New Physics models into the considered scenarios. Furthermore, we consider specific models with tree-level FCNCs mediated by a heavy neutral gauge boson, pseudoscalar or scalar, finding striking differences in the predictions of these scenarios for the observables considered and the correlations among them. We update the Standard Model prediction for the time-integrated branching ratio taking the subtle decay width difference effects into account. We find (3.56 +/- 0.18) x 10^-9, and discuss the error budget.

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arXiv2013

The Anatomy of Neutral Scalars with FCNCs in the Flavour Precision Era

In many extensions of the Standard Model flavour changing neutral current processes can be mediated by tree-level heavy neutral scalars and/or pseudo-scalars H^0(A^0). This generally introduces new sources of flavour violation and CP violation as well as left-handed and right-handed scalar currents. These new physics contributions imply a pattern of deviations from SM expectations for FCNC processes that depends only on the couplings of H^0(A^0) to fermions and on their masses. In situations in which a single H^0 or A^0 dominates NP contributions stringent correlations between Delta F=2 and Delta F=1 observables exist. Anticipating the Flavour Precision Era ahead of us we illustrate this by searching for allowed oases in the landscape of a given model assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze Delta F=2 observables in B^0_{s,d}-bar B^0_{s,d} and K^0-bar K^0 systems and rare B and K decays with charged leptons in the final state including both left-handed and right-handed scalar couplings of H^0 and A^0 to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different scenarios. The prominent role of the decays B_{s,d}-> mu^+ mu^- in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in rare B_{s,d} decays emerges provided M_H< 1 TeV. NP effects in rare K decays are very small. Neutral SM Higgs contributions to rare B and K decays turn out to be negligible once the constraints from Delta F=2 processes are taken into account. Finally, we point out striking differences between the correlations found here and in scenarios in which tree-level FCNC are mediated by a new neutral gauge boson Z'.

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arXiv2013

Stringent Tests of Constrained Minimal Flavour Violation through Delta F=2 Transitions

New Physics contributions to Delta F=2 transitions in models with constrained Minimal Flavour Violation (CMFV), are parametrized by a single variable S(v), the value of the real box diagram function. With already precise experimental values of epsilon_K, Delta M_d, Delta M_s, CP-asymmetry S_{psi K_S} and of hat{B}_K entering the evaluation of epsilon_K, the future of CMFV in the Delta F=2 sector depends crucially on the values of |Vcb|, |Vub|, gamma, F_{B_s} sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}}. The ratio xi of the latter two parameters, rather precisely determined from lattice calculations, allows then together with Delta M_s/Delta M_d and S_{psi K_S} to determine the range of gamma in the unitarity triangle independently of the value of S(v). Imposing in addition the constraints from epsilon_K and Delta M_d allows to determine the favorite CMFV values of |Vcb|, |Vub|, F_{B_s} sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}} as functions of S(v) and gamma. The |Vcb|^4 dependence of epsilon_K allows to determine |Vcb| for a given S(v) and gamma with a higher precision than it is presently possible using tree-level decays. The same applies to |Vub|, |Vtd| and |Vts| that are automatically determined as functions of S(v) and gamma. Typically F_{B_s}sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}} have to be significantly lower than their present lattice values, while |Vcb| has to be significantly higher than its tree-level determination. The region in the space of these three parameters allowed by CMFV indicates visible problems in this class of models and hints for the presence of new sources of flavour violation and/or new local operators in Delta F=2 data that are strongly suppressed in these models. As a byproduct we propose to reduce the present uncertainty in the charm contribution toepsilon_K by using the experimental value of Delta M_K.

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arXiv2013

The Anatomy of Z' and Z with Flavour Changing Neutral Currents in the Flavour Precision Era

The simplest extension of the SM that generally introduces new sources of flavour and CP violation as well as right-handed currents is the addition of a U(1) gauge symmetry to the SM gauge group. If the corresponding heavy gauge boson Z' mediates FCNC processes in the quark sector at tree-level, these new physics contributions imply a pattern of deviations from SM expectations for FCNC processes depending only on Z' couplings to fermions and on its mass. This implies stringent correlations between Delta F=2 and Delta F=1 observables which govern the landscape of the allowed parameter space for Z'-models. Anticipating the Flavour Precision Era (FPE) ahead of us we illustrate this by searching for allowed oases in this landscape assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze Delta F=2 observables in K^0-bar K^0 and B^0_{s,d}-bar B^0_{s,d} systems and rare K and B decays including both left-handed and right-handed Z'-couplings to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different Z' scenarios. The important role of b->s l^+ l^- and b->s nu bar nu transitions in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in B_{s,d} and K meson systems emerges provided M_Z'<3 TeV. While for M_Z'>5 TeV Z' effects in rare B_{s,d} decays are found typically below 10% and hard to measure even in the FPE, K->pi nu bar nu and K_L-> pi^0 l^+ l^- decays provide an important portal to scales beyond those explored by the LHC. We apply our formalism to NP scenarios with induced flavour changing neutral Z-couplings to quarks. We find that in the case of B_d and K decays, but not B_s decays, such Z-couplings still allow for sizable departures from the SM.

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arXiv2013

Particle-Antiparticle Mixing, CP Violation and Rare K and B Decays in a Minimal Theory of Fermion Masses

We present a detailed study of Delta F=2 observables and of rare K^+(K_L) and B_{s,d} meson decays in a "Minimal Theory of Fermion Masses" (MTFM). In this theory Yukawa couplings are generated through the mixing with heavy vectorlike (VF) fermions. This implies corrections to the SM quark couplings to W, Z and Higgs so that FCNC processes receive contributions from tree level Z and Higgs exchanges and W bosons couple to right-handed quarks. In a particular version of this model in which the Yukawa matrix lambda^D in the heavy down fermion sector is unitary, lambda^U =1 and M = M_{VF} is fixed, only three real and positive definite parameters describe New Physics (NP) contributions to all Delta F=2 and Delta F=1 observables in K and B_{s,d} systems once the known quark masses and the CKM matrix are correctly reproduced. For M>1 TeV NP contributions to B_{s,d}^0- bar{B}_{s,d}^0 mixings are found to be very small. While in principle NP contributions to epsilon_K and Delta F=1 processes could be large, the correlation between epsilon_K and K_L->mu^+ mu^- eliminates basically NP contributions to epsilon_K and right-handed current contributions to Delta F=1 FCNC observables. We find CMFV structure in B_{s,d} decays with BR(B_{s,d}->mu^+ mu^-) uniquely enhanced for M=3 TeV by at least 35% and almost up to a factor of two over their SM values. Also BR(K^+->pi^+ bar{nu} nu) and BR(K_L->pi^0 bar{nu} nu)$ are uniquely enhanced by similar amount but the correlation between them differs from the CMFV one. We emphasize various correlations between K and B_{s,d} decays that could test this scenario. The model favours gamma=68°, |V_{ub}|=0.0037, S_{psi K_S}=0.72, S_{psi phi}=0.04 and 4.2*10^-9 mu^+ mu^-)<5.0*10^-9 for M=3-4 TeV.

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arXiv2013

On the Correlations between Flavour Observables in Minimal U(2)^3 Models

The stringent correlations between flavour observables in models with CMFV are consistent with the present data except for the correlation Delta M_{s,d}-epsilon_K. Motivated by the recent work of Barbieri et al, we compare the CMFV correlations with the ones present in a special class of models with an approximate global U(2)^3 flavour symmetry, constrained by a minimal set of spurions governing the breakdown of this symmetry and the assumption that only SM operators are relevant in flavour physics. This analog of CMFV to be called MU(2)^3 allows to avoid the Delta M_{s,d}-epsilon_K tension in question because of reduced flavour symmetry and implied non-MFV contributions to Delta M_{s,d}. While the patterns of flavour violation in K meson system is the same as in CMFV models, the CP-violation in B_{s,d} meson systems can deviate from the one in the SM and CMFV models. We point out a stringent triple S_{psi K_S}-S_{psi phi}-|V_ub| correlation in this class of models that could in the future provide a transparent distinction between different MU(2)^3 models and in the context of these models determine |V_ub| by means of precise measurements of S_{psi K_S} and S_{psi phi} with only small hadronic uncertainties. For fixed S_{psi K_S} the correlation between B(B^+ -> tau^+nu_tau) and S_{psi phi} follows. We also find that MU(2)^3 models could in principle accommodate a negative value of S_{psi phi}, provided |V_ub| is found to be in the ballpark of exclusive determinations and the particular MU(2)^3 model provides a 25% enhancement of epsilon_K. A supersymmetric U(2)^3 model worked out in the Barbieri-School appears to satisfy these requirements. However if B(B^+ -> tau^+nu_tau)>1.0 10^{-4} will be confirmed by future experiments only positive S_{psi phi} is allowed in this framework. We summarize briefly the pattern of flavour violation in rare K and B_{s,d} decays in MU(2)^3 models.

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arXiv2012

Photon Structure Functions: 1978 AND 2005

I describe the early days of the photon structure functions. In particular I discuss the parton model result of Walsh and Zerwas (1973), leading order QCD calculation of Witten (1976) and next-to-leading QCD calculation of Bardeen and myself (1978). A very brief summary of the progress made from 1978 until 2005 is also given.

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arXiv2012

The Anatomy of Quark Flavour Observables in 331 Models in the Flavour Precision Era

The coming flavour precision era will allow to uncover various patterns of flavour violation in different New Physics (NP) scenarios that are presently washed out by hadronic and experimental uncertainties. We illustrate this by performing the anatomy of flavour violation in the 331 models, based on the gauge group SU(3)_C X SU(3)_L X U(1)_X that are among the simplest NP scenarios with new sources of flavour and CP violation. The latter originate dominantly through the flavour violating interactions of ordinary quarks and leptons with a new heavy Z' gauge boson. After discussing first these models in some generality, we present a detailed study of Delta F=2 observables and of rare K and B meson decays in the specific beta=1/\sqrt{3} model (to be called overline{331} model) assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. The most prominent roles in our analysis play epsilon_K, Delta M_q (q=d,s), the mixing induced CP asymmetries S_{psi K_S} and S_{psi phi}, rare decays B_{s,d}-> mu^+ mu^- and in particular the CP-asymmetry S_{mu^+ mu^-}^s in B_s ->mu^+ mu^-. We identify a number of correlations between various observables that differ from those known from CMFV models. While, the Delta F=2 observables allow still for four oases in the new parameter space, we demonstrate how the inclusion of Delta F=1 observables can in the future identify the optimal oasis for this model. For 1 TeV <= M_{Z'}<= 3 TeV the overline{331} model is in good agreement with the recent data for B^+->tau^+ nu_tau, it removes the epsilon_K-S_{psi K_S} tension present in the SM and the epsilon_K-Delta M_{s,d} tension present in CMFV models. Simultaneously, while differing from the SM, it is consistent with the present data on BR(B_{s,d}->mu^+ mu^-) and S_{psi phi}. We identify the triple correlation BR(B_s->mu^+ mu^-)-S_{psi phi}-S_{mu^+ mu^-}^s.

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arXiv2012

On the Standard Model prediction for BR(B{s,d} to mu+ mu-)

The decay Bs to mu+ mu- is one of the milestones of the flavor program at the LHC. We reappraise its Standard Model prediction. First, by analyzing the theoretical rate in the light of its main parametric dependence, we highlight the importance of a complete evaluation of higher-order electroweak corrections, at present known only in the large-mt limit, and leaving sizable dependence on the definition of electroweak parameters. Using insights from a complete calculation of such corrections for K to pi bar{nu} nu decays, we find a scheme in which NLO electroweak corrections are likely to be negligible. Second, we address the issue of the correspondence between the initial and the final state detected by the experiments, and those used in the theoretical prediction. Particular attention is devoted to the effect of the soft radiation, that has not been discussed for this mode in the previous literature, and that can lead to O(10%) corrections to the decay rate. The "non-radiative" branching ratio (that is equivalent to the branching ratio fully inclusive of bremsstrahlung radiation) is estimated to be (3.23 +/- 0.27) x 10^{-9} for the flavor eigenstate, with the main uncertainty resulting from the value of f_{Bs}, followed by the uncertainty due to higher order electroweak corrections. Applying the same strategy to Bd to mu+ mu-, we find for its non-radiative branching ratio (1.07 +/- 0.10) x 10^{-10}.

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arXiv2012

BSM models facing the recent LHCb data: A first look

During last decade a number of detailed analyses of flavour observables and of their correlations within more than a dozen specific BSM models have been performed at the TUM. One of the goals of these analyses was to investigate which model is capable of obtaining large mixing induced CP asymmetry in the B_s system, S_{psi phi}, and to find out what this would imply for other flavour observables. In this context also the rare decays B_{s,d}->mu^+ mu^- have been considered. In some models their branching ratios can be enhanced by orders of magnitude above the SM expectations. The recent data on S_{psi phi} and B_{s,d}-> mu^+ mu^- from the LHCb put an end to these very optimistic hopes modifying significantly the allowed patterns of deviations from SM predictions for flavour observables in concrete BSM models. We make a first semi-quantitative assessment of the most important modifications in the predictions of the BSM models in question including also recently analyzed models and taking into account the most recent lattice input. For some BSM models the LHCb data turned out to be a relief. On the other hand the SM, models with CMFV and MFV models without flavour blind phases appear to have significant difficulties in describing all Delta F=2 observables in B_{s,d} and K^0 meson systems simultaneously. We propose to regard the stringent CMFV relations between various observables as standard candels of flavour physics. The pattern of deviations from these relations may help in identifying the correct NP scenario.

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arXiv2012

Delta F = 2 observables and B -> X_q gamma decays in the Left-Right Model: Higgs particles striking back

We present a complete study of Delta S = 2 and Delta B = 2 processes in the left-right model (LRM) based on the weak gauge group SU(2)_L x SU(2)_R x U(1)_{B-L}. This includes epsilon_K, Delta M_K, Delta M_q, A_{SL}^q, Delta Gamma_q with q=d,s and the CP asymmetries S_{psi K_S} and S_{psi phi}. Compared to the Standard Model (SM) these observables are affected by tree level contributions from heavy neutral Higgs particles (H^0) as well as new box diagrams with W_R gauge boson and charged Higgs (H^\pm) exchanges. We also analyse the B -> X_{s,d} gamma decays that receive important new contributions from the W_L-W_R mixing and H^\pm exchanges. Compared to the existing literature the novel feature of our analysis is the search for correlations between various observables that could help us to distinguish this model from other extensions of the SM and to obtain an insight into the structure of the mixing matrix V^R that governs right-handed currents. We find that even for M_{H^0} ~ M_{H^\pm} ~ O(20)TeV, the tree level H^0 contributions to Delta F = 2 observables are by far dominant and the H^\pm contributions to B -> X_q gamma can be very important, even dominant for certain parameters of the model. While in a large fraction of the parameter space this model has to struggle with the experimental constraint from epsilon_K, we demonstrate that there exist regions in parameter space which satisfy all existing Delta F = 2, B -> X_{s,d} gamma, tree level decays and electroweak precision constraints for scales M_{W_R}\simeq2-3TeV in the reach of the LHC. We also show that the S_{psi K_S} - epsilon_K tension present in the SM can be removed in the LRM. However, we point out that the LRM cannot help in explaining the difference between the inclusive and exclusive determinations of |V_{ub}|, when all constraints are taken into account. Finally we present a rather complete list of Feynman rules.

hep-ph↗