1,721,059 research outputs found
Summary of hints for new physics from (quark) flavour physics
No full textRecently 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. <br/
Unparticles at heavy flavor scales: CP violating phenomena
No full textCoupling the scale invariant unparticle sector to flavor physics and assuming that it remains scale invariant I investigate its consequences in heavy flavor physics. A characteristic feature of unparticle physics is a CP-even phase leading to novel CP violating phenomena. The phase is large, based on the assumption that the unparticle sector is strongly self-coupled. I consider the CP asymmetry in the leptonic decay B+ ?+? and the hadronic decay Bd ?D+D-, taking into account constraints of branching ratios and time dependent CP asymmetries. It turns out that the CP asymmetry can be very large even for small couplings because the unparticle interaction term has a lower scaling dimension than the four-Fermi weak interaction term. CP asymmetries in leptonic decays such as B+ ? ?+ v are neither experimentally searched for nor predicted by any other model. I show that the novel CP violation is consistent with the CPT theorem. I identify the CP compensating mode in the unparticle sector and explicitly demonstrate the exact cancellation as demanded by the CPT theore
B -> K* Gamma vs B -> rho Gamma
No full textZwicky, Roman. (2012). B -> K* Gamma vs B -> rho Gamma. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/130126
Unparticle and Higgs boson as composites
No full textWe 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 unification of these two sectors at a much higher scale resembling extended technicolor models. By construction our extensions are natural, meaning that there is no hierarchy problem. The coupling of the unparticle sector to the composite Higgs emerges as a four-Fermi 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 cutoff 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.<br/
Exploiting the width difference in Bs???
Full text linkThe photon polarization in B?V? is a sensitive probe of right-handed currents. In the time dependent decay rate of Bs?phi? the coefficients S and H in front of the sin(?mst) and the sinh(??s/2t) terms are sensitive to those right-handed currents. As compared to the Bd system there is a sizable width difference in Bs 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 ??s/?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 Bs mesons which has considerable experimental advantages as no flavour tag will be required. The resolution on H is inversely proportional to the Bs width difference ??s. These experimental prospects have to be compared with the Standard Model predictions Sphi?=0±0.002 and Hphi?=0.047±0.025+0.015 presented in this Letter. We also give the Standard Model prediction and the experimental sensitivity for the direct CP asymmetry in Bs?phi?
Exclusive chromomagnetism in heavy-to-light FCNCs
No full textWe compute matrix elements of the chromomagnetic operator, often denoted by O 8 , between B/D states and light mesons plus an off-shell photon by employing the method of light-cone sum rules at leading twist-2. These matrix elements are relevant for processes such as B?K ? l + l ? and they can be seen as the analogues of the well-known penguin form factors T 1,2,3 and f T . We find a large CP -even phase for which we give a long-distance interpretation. We compare our results to QCD factorization for which the spectator photon emission is end-point divergent. The analytic structure of the correlation function used in our method admits a complex anomalous threshold on the physical sheet. The meaning and handling within the sum rule approach of the anomalous threshold is discussed
Discrete minimal flavour violation
No full textWe investigate the consequences of replacing the global flavor symmetry of minimal flavor violation (MFV) SU(3)Q×SU(3)U×SU(3)D×[centered ellipsis] by a discrete [script D]Q×[script D]U×[script D]D×[centered ellipsis] symmetry. Goldstone bosons resulting from the breaking of the flavor symmetry generically lead to bounds on new flavor structure many orders of magnitude above the TeV scale. The absence of Goldstone bosons for discrete symmetries constitute the primary motivation of our work. Less symmetry implies further invariants and renders the mass-flavor basis transformation observable in principle and calls for a hierarchy in the Yukawa matrix expansion. We show, through the dimension of the representations, that the (discrete) symmetry in principle does allow for additional DeltaF=2 operators. If though the DeltaF=2 transitions are generated by two subsequent DeltaF=1 processes, as, for example, in the standard model, then the four crystal-like groups Sigma(168)[approximate]PSL(2,[openface F]7), Sigma(72phi), Sigma(216phi) and especially Sigma(360phi) do provide enough protection for a TeV-scale discrete MFV scenario. Models where this is not the case have to be investigated case by case. Interestingly Sigma(216phi) has a (nonfaithful) representation corresponding to an A4 symmetry. Moreover we argue that the, apparently often omitted, (D) groups are subgroups of an appropriate Delta(6g2). We would like to stress that we do not provide an actual model that realizes the MFV scenario nor any other theory of flavor
Hyperscaling relations in mass-deformed conformal gauge theories
No full textWe present a number of analytical results which should guide the interpretation of lattice data in theories with an infrared fixed point (IRFP) deformed by a mass term δL = -m q‾ q. From renormalization group (RG) arguments we obtain the leading scaling exponent, F ~ m ηF, for all decay constants of the lowest lying states other than the ones affected by the chiral anomaly and the tensor ones. These scaling relations provide a clear cut way to distinguish a theory with an IRFP from a confining theory with heavy fermions. Moreover, we present a derivation relating the scaling of ⟨q‾q⟩ ~ m ηq‾q to the scaling of the density of eigenvalues of the massless Dirac operator ρ(λ) ~ λ ηq‾q. RG arguments yield ηq‾q = (3-γ*)/(1+γ*) as a function of the mass anomalous dimension γ* at the IRFP. The arguments can be generalized to other condensates such as ⟨G2⟩ ~ m4/(1+γ*). We describe a heuristic derivation of the result on the condensates, which provides interesting connections between different approaches. Our results are compared with existing data from numerical studies of SU(2) with two adjoint Dirac fermions
Electroweak precision data and the Lee-Wick standard model
No full textWe 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 class of models that assumes a so-called “universal” form which can be described by seven oblique parameters at leading order in mW2/M1,22. At tree level we find that Y=-mW2/M12 and W=-mW2/M22, where the negative sign is due to the presence of the negative norm states. All other oblique parameters (S?,X) and (T?,U?,V) are found to be zero. In the addendum we show how our results differ from previous investigations, where contact terms, which are found to be of leading order, have been neglected. 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 M1?M2?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?)2 factor and are therefore not expected to change the constraints on M1 and M2. This assertion is most transparent from the higher derivative formulation of the theory
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