arXiv subjects

Roman Zwicky

Publications and source records attributed to Roman Zwicky.

71 records · Page 4Linked to original sources

arXiv2009

Electroweak Precision Data and the Lee-Wick Standard Model

We investigate the electroweak precision constraints on the recently proposed Lee-Wick Standard Model at tree level. We analyze low energy, Z-pole (LEP1/SLC) and LEP2 data separately. We derive the exact tree level low energy and Z-pole effective Lagrangians from both the auxiliary field and higher derivative formulation of the theory. For the LEP2 data we use the fact that the Lee-Wick Standard Model belongs to the so-called 'universal class' which can be described by seven oblique parameters at leading order in m_W^2/M_{1,2}^2. At tree level we find that the only non-zero oblique parameters are Y = -m_W^2/M_1^2 and W = -m_W^2/M_2^2, where the negative sign is due to the presence of the negative norm states. The Lee-Wick operators do not violate the SU(2)_L or custodial symmetry at tree level implying S=0 and T=0 respectively. Our results differ substantially from a prior analysis in this respect. We show a plot including all three constraints. The LEP1/SLC constraints are slightly stronger than LEP2 and much stronger than the low energy ones. The LEP1/SLC results exclude gauge boson masses of M_1 ~ M_2 ~ 3 TeV at the 99% confidence level. Somewhat lower masses are possible when one of the masses assumes a large value. Loop corrections to the electroweak observables are suppressed by the standard ~1/(4 π)^2 factor and are therefore not expected to change the constraints on M_1 and M_2. This assertion is most transparent from the higher derivative formulation of the theory.

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arXiv2008

Unparticle & Higgs as Composites

We propose a generic framework in which the Higgs and the unparticle are both composite. The underlying theories are four dimensional, asymptotically free, nonsupersymmetric gauge theories with fermionic matter. We sketch a possible uni- fication of these two sectors at a much higher scale resembling extended technicolor models. By construction our extensions are natural, meaning that there is no hierar- chy problem. The coupling of the unparticle sector to the composite Higgs emerges as a four-fermion operator. The bilinear unparticle operator near the electroweak scale has scaling dimension in the range 1 < dU < 3. We investigate, in various ways, the breaking of scale invariance induced by the electroweak scale resulting in an unparticle condensate. The latter acts as a natural infrared cut off or hadronic scale. We give the low-energy effective theory valid near the electroweak scale. The unparticle Higgs mixing is found to be suppressed within our framework.

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arXiv2008

Summary of hints for new physics from (quark) flavour physics

Recently two hints for new physics have emerged: The B_s mixing phase phi_s and the rate of D_s -> (mu,tau) nu exposing a discrepancy of \sim 3 sigma and 3.8 sigma deviation from the Standard Model respectively. Moreover the difference of the CP asymmetries in B -> K pi between the charged and neutral modes is at the 5.3 sigma level which is somewhat larger than expected. New physics in phi_s or A_CP(B -> K pi) would be in contradiction with the minimal flavour violation hypothesis. The latter has recently attracted attention because of the absence of deviation in CP and flavour violation in the quark sector.

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arXiv2008

Exploiting the width difference in B_s -> phi gamma

The photon polarization in B -> V gamma is a sensitive probe of right-handed currents. In the time dependent decay rate of B_s -> phi gamma the coefficients S and H in front of the sin(Delta m_s t) and the sinh(Delta Gamma_s /2 t) terms are sensitive to those right-handed currents. As compared to the B_d system there is a sizable width difference in B_s mesons which leads to the additional measurable observable H. We show with a Monte Carlo simulation that the expected resolution on S and H will be about 0.15 at the LHCb experiment for Delta Gamma_s/Gamma_s = 0.15 and a data sample of 2 fb^{-1}. We also show that the observable H can be measured from the untagged decay rate of B_s mesons which has considerable experimental advantages as no flavour tag will be required. The resolution on H is inversely proportional to the B_s width difference Delta Gamma_s. These experimental prospects have to be compared with the Standard Model predictions S_{phi gamma} = 0 \pm 0.002 and H_{phi γ} = 0.047 \pm 0.025+0.015 presented in this paper. We also give the Standard Model prediction and the experimental sensitivity for the direct CP asymmetry in B_s -> phi gamma.

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arXiv2007

Unparticles and CP-violation

We give a brief summary of the unparticle scenario proposed by Georgi. The CP-even phase of the propagator is exploited to study the CP-asymmetry in B+ --> tau+ + nu, which is neither experimentally searched for nor predicted by any other model. Furthermore we show that the novel CP-violation is consistent with the CPT theorem by identifying the CP-compensating mode in the unparticle sector.

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arXiv2007

Unparticles at heavy flavour scales: CP violating phenomena

Coupling the scale invariant unparticle sector to flavour physics and assuming that it remains scale invariant we investigate its consequences in heavy flavour physics. A drastic feature of unparticle physics is an unusual phase leading to novel CP violating phenomena. We consider the CP asymmetry in the leptonic decay B^+ -> tau^+ nu and the hadronic decay B_d -> D^+D^-, taking into account constraints of branching ratios and time dependent CP asymmetries. Generic plots are shown and it turns out that there exist parameters for which the CP violation is maximal. A prediction of a large CP asymmetry in B_d -> D^+D^- is difficult to achieve in other models without contradicting the current data in other channels. The prediction of a CP asymmetry in leptonic decays, such as B^+ -> tau^+ nu, is novel. We identify the CP compensating mode due to the unparticles and show explicitly that it exactly cancels the CP asymmetry of B^+ -> tau^+ nu as demanded by CPT invariance. Building up on earlier works we investigate the breaking of scale invaricance, due to the coupling to the Higgs and the size of the effects in the weak sector resorting to a dimensional analysis. An enhancement is observed on the grounds of the relevance of the unparticle interaction operator as compared to the weak four-Fermi term.

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arXiv2007

B->V gamma Beyond QCD Factorisation

We calculate the main observables in $B_{u,d}\to (ρ,ω,K^*)γ$ and $B_s\to (\bar K^*,ϕ)γ$ decays, i.e. branching ratios and CP and isospin asymmetries. We include QCD factorisation results and also the dominant contributions beyond QCD factorisation, namely long-distance photon emission and soft-gluon emission from quark loops. All contributions beyond QCD factorisation are estimated from light-cone sum rules. We devise in particular a method for calculating soft-gluon emission, building on earlier ideas developed for analogous contributions in non-leptonic decays. Our results are relevant for new-physics searches at the $B$ factories, the LHC and a future super-flavour factory. Using current experimental data, we also extract $|V_{td}/V_{ts}|$ and the angle $γ$ of the unitarity triangle. We give detailed tables of theoretical uncertainties of the relevant quantities which facilitates future determinations of these CKM parameters from updated experimental results.

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arXiv2006

Time-dependent CP Asymmetry in B->K* gamma as a (Quasi) Null Test of the Standard Model

We calculate the dominant Standard Model contributions to the time-dependent CP asymmetry in B0->K*0 gamma, which is O(1/mb) in QCD factorisation. We find that, including all relevant hadronic effects, in particular from soft gluons, the asymmetry S is very small, S=-0.022\pm 0.015^{+0}_{-0.01}, and smaller than suggested recently from dimensional arguments in a 1/mb expansion. Our result implies that any significant deviation of the asymmetry from zero, and in particular a confirmation of the current experimental central value, S_{HFAG}=-0.28\pm 0.26, would constitute a clean signal for new physics.

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arXiv2006

|V_td/V_ts| from B-> V gamma

The dominant theoretical uncertainty in extracting |V_td/V_ts| from the ratio of branching ratios R=B(B->(rho,omega)gamma)/B(B->K* gamma) is given by the ratio of form factors xi=T_1^{B->K*}(0)/T_1^{B->rho}(0). We re-examine xi in the framework of QCD sum rules on the light-cone, taking into account hitherto neglected SU(3)-breaking effects. We find xi=1.17 \pm 0.09. Using QCD factorisation for the branching ratios, and the current experimental average for R quoted by HFAG, this translates into |V_td/V_ts|^HFAG_{B->V gamma} = 0.192 \pm 0.014(th) \pm 0.016(exp). This result agrees, within errors, with that obtained from the Standard Model unitarity triangle, |V_td/V_ts|_SM = 0.216 \pm 0.029, based on tree-level-only processes, and with |V_td/V_ts|_{Delta m} = 0.2060^{+0.0081}_{-0.0060}(th) \pm 0.0007(exp), from the CDF measurement of B_s oscillations.

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arXiv2006

B -> K* gamma vs B -> rho gamma and |V_td/V_ts|

We determine |V_{\rm td}/V_{\rm ts}| = 0.192 \pm 0.016_ exp \pm 0.014_th from B -> (K^*,rho) gamma as measured by the B-factories Babar and Belle. This version differs from the original proceedings by the inclusion of the new BaBar measurement of B -> rho(omega) gamma presented at ICHEP 2006, which significantly shifts the results for |V_{td}/V_{ts}|.

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arXiv2006

Operator Relations for SU(3) Breaking Contributions to K and K* Distribution Amplitudes

We derive constraints on the asymmetry a1 of the momentum fractions carried by quark and antiquark in K and K* mesons in leading twist. These constraints follow from exact operator identities and relate a1 to SU(3) breaking quark-antiquark-gluon matrix elements which we determine from QCD sum rules. Comparing our results to determinations of a1 from QCD sum rules based on correlation functions of quark currents, we find that, for a1^\parallel(K*) the central values agree well and come with moderate errors, whereas for a1(K) and a1^\perp(K*) the results from operator relations are consistent with those from quark current sum rules, but come with larger uncertainties. The consistency of results confirms that the QCD sum rule method is indeed suitable for the calculation of a1. We conclude that the presently most accurate predictions for a1 come from the direct determination from QCD sum rules based on correlation functions of quark currents and are given by: a1(K) = 0.06\pm 0.03, a1^\parallel(K*) = 0.03\pm 0.02, a1^\perp(K*) = 0.04\pm 0.03.

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arXiv2005

SU(3) Breaking of Leading--Twist K and K* Distribution Amplitudes - a Reprise

We review the status of the leptonic decay constants f_K and f_K^{\parallel,\perp} of the K and K*, respectively, and the SU(3) breaking quantities a_1(K) and a_{1}^{\parallel,\perp}(K*), the first Gegenbauer-moments of the leading-twist distribution amplitudes of K and K*. We obtain new predictions from QCD sum rules which are relevant for the calculation of K and K* form factors, for instance T_1^{B->K*}, which determines the decay B -> K* gamma, and for QCD factorisation calculations of nonleptonic B decays into strange mesons, for instance B -> K pi.

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arXiv2005

|V_ub| and Constraints on the Leading-Twist Pion Distribution Amplitude from B->pi l nu

Using new experimental data on the leptonic mass spectrum of B->pi l nu, we simultaneously determine |V_ub| and constrain a_2^pi and a_4^pi, the first two Gegenbauer moments of the pion's leading-twist distribution amplitude. We find |V_ub| = (3.2\pm 0.1\pm 0.1\pm 0.3) 10^-3, where the first error is experimental, the second comes from the shape of the form factor in q^2 and the third is a 8% uncertainty from the normalisation of the form factor. We also find a_2^pi(1 GeV)=0.19\pm 0.19 and a_4^pi(1 GeV)\geq -0.07.

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arXiv2004

B_{d,s}->rho, omega, K*, phi Decay Form Factors from Light-Cone Sum Rules Revisited

We present an improved calculation of $B\to$ light vector form factors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is typically 10% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters. We present our results in a way which details the dependence of the form factors on these parameters and facilitates the incorporation of future updates of their values from e.g. lattice calculations. We also give simple and easy-to-inplement parametrizations of the $q^2$-dependence of the form factors which are valid in the full kinematical regime of $q^2$.

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arXiv2004

B->pi,K,eta Decay Formfactors from Light-Cone Sum Rules

We present an improved calculation of all B -> light pseudoscalar formfactors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is 10 to 13%. The dependence of the formfactors on the momentum transfer q^2 is parametrized in a simple way that is consistent with their analytical properties and is valid for all physical q^2. The uncertainty of the extrapolation in q^2 on the semileptonic decay rate Gamma(B -> pi e nu) is estimated to be 5%.

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arXiv2004

New Results on B->pi, K, eta Decay Formfactors from Light-Cone Sum Rules

We present an improved calculation of $B\to$ light pseudoscalar formfactors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is 10 to 13% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters, in particular those describing the twist-2 distribution amplitudes of the pi, K and eta. We present our results in a way which details the dependence of the formfactors on these parameters and facilitates the incorporation of future updates of their values from e.g. lattice calculations.

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arXiv2001

Improved Analysis of B->pi e nu from QCD Sum Rules on the Light-Cone

We present a new calculation of the B->pi form-factor f_+, relevant for the measurement of |V_{ub}| from semileptonic B->pi transitions, from QCD sum rules on the light-cone. The new element is the calculation of radiative corrections to next-to-leading twist-3 accuracy. We find that these contributions are factorizable at O(alpha_s), which lends additional support to the method of QCD sum rules on the light-cone. We obtain f_+(0) = 0.26\pm 0.06 \pm 0.05, where the first error accounts for the uncertainty in the input-parameters and the second is a guesstimate of the systematic uncertainty induced by the approximations inherent in the method. We also obtain a simple parametrization of the form-factor which is valid in the entire kinematical range of semileptonic decays and consistent with vector-meson dominance at large momentum-transfer.

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