Martín González-Alonso

Probing Novel Scalar and Tensor Interactions from (Ultra)Cold Neutrons to the LHC

Scalar and tensor interactions were once competitors to the now well-established V-A structure of the Standard Model weak interactions. We revisit these interactions and survey constraints from low-energy probes (neutron, nuclear, and pion decays) as well as collider searches. Currently, the most stringent limit on scalar and tensor interactions arise from 0+ -> 0+ nuclear decays and the radiative pion decay pi -> e nu gamma, respectively. For the future, we find that upcoming neutron beta decay and LHC measurements will compete in setting the most stringent bounds. For neutron beta decay, we demonstrate the importance of lattice computations of the neutron-to-proton matrix elements to setting limits on these interactions, and provide the first lattice estimate of the scalar charge and a new average of existing results for the tensor charge. Data taken at the LHC is currently probing these interactions at the 10^-2 level (relative to the standard weak interactions), with the potential to reach the 10^-3 level. We show that, with some theoretical assumptions, the discovery of a charged spin-0 resonance decaying to an electron and missing energy implies a lower limit on the strength of scalar interactions probed at low energy.

Non-standard charged current interactions: beta decays versus the LHC

A bstractWe discuss low-energy and collider constraints on the effective couplings characterizing non-standard charged current interactions. A direct comparison of low-energy and LHC probes can be performed within an effective theory framework, when the new physics mediating these interactions originates in the multi-TeV scale. We find that for the effective couplings involving right-handed neutrinos the LHC bounds from pp → e + MET + X are at the (sub)percent level, already stronger than those from β decays. For operators involving left-handed neutrinos, the (axial-)vector and pseudo-scalar effective couplings are best probed at low energy, while scalar and tensor couplings are currently probed at the same level by beta decays and the LHC channels pp → e + MET + X and, by using SU(2) gauge invariance, pp → e+e− + X. Future beta decay experiments at the 0.1% level or better will compete in sensitivity with higher statistics and higher energy data from the LHC.

Determination of the Chiral Couplings L_10 and C_87 from Semileptonic Tau Decays

Using recent precise hadronic � -decay data on the VA spectral function, and general properties of QCD such as analyticity, the operator product expansion, and chiral perturbation theory, we get accurate values for the QCD chiral order parameters L r ðM� Þ and C r ðM� Þ. These two low-energy constants appear at order p 4 and p 6 , respectively, in the chiral perturbation theory expansion of the VA correlator. At order p 4 we obtain L r ðM� Þ¼� ð 5:22 � 0:06 Þ� 10 � 3 . Including in the analysis the two-loop (order p 6 ) contributions, we get L r ðM� Þ¼� ð 4:06 � 0:39 Þ� 10 � 3 and C r ðM� Þ¼ð 4:89 � 0:19 Þ� 10 � 3 GeV � 2 . In the SU(2) chiral effective theory, the corresponding low-energy coupling takes the value � l5 ¼ 13:30 � 0:11 at order p 4 , and � l5 ¼ 12:24 � 0:21 at order p 6 .

Leptophobic Z' Boson and Parity-Violating eD Scattering

We study the impact of a leptophobic Z′ gauge boson on the C1q and C2q parameters that describe the low-energy, parity-violating electron-quark neutral current interaction. We complement previous work by including the penguin-like vertex corrections, thereby completing the analysis of one-loop calculation up to O(m^(2)_(q′)/M^(2)_(Z′)) terms. We analyze the sensitivity of these probes to the different couplings Z′u q (q=u, c, t) and Z′d q (q=d, s, b) in a model-independent way that can be applied to any specific Z′ scenario. We show that constraints from neutral kaon and heavy flavor studies preclude significant contributions from flavor nondiagonal couplings except for those involving top quarks. We apply our results to a light Z′ with flavor diagonal couplings to up or down quarks, a scenario proposed in the literature to explain the CDF W plus dijet anomaly. We find that such a particle would not affect the C_1q coefficients, but it would have a sizable impact on C_2q couplings that can be probed by future measurements of parity-violating deep inelastic scattering of polarized electrons off of deuterium.

U(2)⁵ flavor symmetry and lepton universality violation in W→τν̄τ

The seeming violation of universality in the τ lepton coupling to the W boson suggested by LEP-II data is studied using an effective field theory (EFT) approach. Within this framework we explore how this feature fits into the current constraints from electroweak precision observables using different assumptions about the flavor structure of New Physics, namely [U(2)×U(1)]⁵ and U(2)⁵. We show the importance of leptonic and semileptonic tau decay measurements, giving 3–4 TeV bounds on the New Physics effective scale at 90% C.L. We conclude under very general assumptions that it is not possible to accommodate this deviation from universality in the EFT framework, and thus such a signal could only be explained by the introduction of light degrees of freedom or New Physics strongly coupled at the electroweak scale.

Kinematic sensitivity to the Fierz term of β -decay differential spectra

The current most stringent constraints on exotic scalar or tensor couplings in neutron and nuclear

Duality violation in QCD Sum Rules with the LR correlator

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β decays in the LHC era: From ultracold neutrons to colliders

decay, involving left-handed neutrinos, are obtained from the Fierz interference term. The sensitivity to this term in a correlation coefficient is usually driven by an energy-averaged kinematic factor that increases monotonically toward smaller values of the

Quark-hadron duality violation in QCD Sum Rules with hadronic \tau data

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From Hadronic τ Decays to the Chiral Couplings and

endpoint energies. We first point out here that this property does not hold for certain differential observables that are directly sensitive to the Fierz term, such as the