Search

Using an effective field theory approach, we study coherent neutrino scattering on nuclei, in the setup pertinent to the COHERENT experiment. We include non-standard effects both in neutrino production and detection, with an arbitrary flavor structure, with all leading Wilson coefficients simultaneously present, and without assuming factorization in flux times cross section. A concise description of the COHERENT event rate is obtained by introducing three generalized weak charges, which can be associated (in a certain sense) to the production and scattering of $\nu_e$, $\nu_\mu$ and $\bar{\nu}_\mu$ on the nuclear target. Our results are presented in a convenient form that can be trivially applied to specific New Physics scenarios. In particular, we find that existing COHERENT measurements provide percent level constraints on two combinations of Wilson coefficients. These constraints have a visible impact on the global SMEFT fit, even in the constrained flavor-blind setup. The improvement, which affects certain 4-fermion LLQQ operators, is significantly more important in a flavor-general SMEFT. Our work shows that COHERENT data should be included in electroweak precision studies from now on., Comment: 52 pages, 7 figures, 3 tables, typos corrected

We discuss the effective field theory (EFT) for nuclear beta decay. The general quark-level EFT describing charged-current interactions between quarks and leptons is matched to the nucleon-level non-relativistic EFT at the O(MeV) momentum scale characteristic for beta transitions. The matching takes into account, for the first time, the effect of all possible beyond-the-Standard-Model interactions at the subleading order in the recoil momentum. We calculate the impact of all the Wilson coefficients of the leading and subleading EFT Lagrangian on the differential decay width in allowed beta transitions. As an example application, we show how the existing experimental data constrain the subleading Wilson coefficients corresponding to pseudoscalar, weak magnetism, and induced tensor interactions. The data display a 3.5 sigma evidence for nucleon weak magnetism, in agreement with the theory prediction based on isospin symmetry., Comment: 55 pages; V2: corrected tensor matrix element, discussion of matrix elements expanded in Appendix A; V3: Discussion of many-body currents added in Appendix D. Published version

Hadronic $\tau$ decays are studied as probe of new physics. We determine the dependence of several inclusive and exclusive $\tau$ observables on the Wilson coefficients of the low-energy effective theory describing charged-current interactions between light quarks and leptons. The analysis includes both strange and non-strange decay channels. The main result is the likelihood function for the Wilson coefficients in the tau sector, based on the up-to-date experimental measurements and state-of-the-art theoretical techniques. The likelihood can be readily combined with inputs from other low-energy precision observables. We discuss a combination with nuclear beta, baryon, pion, and kaon decay data. In particular, we provide a comprehensive and model-independent description of the new physics hints in the combined dataset, which are known under the name of the Cabibbo anomaly., Comment: 58 pages; V2: Table 1 added, final published version

We investigate the sensitivity of the FASER$\nu$ detector to new physics in the form of non-standard neutrino interactions. FASER$\nu$, which has recently been installed 480 m downstream of the ATLAS interaction point, will for the first time study interactions of multi-TeV neutrinos from a controlled source. Our formalism -- which is applicable to any current and future neutrino experiment -- is based on the Standard Model Effective Theory~(SMEFT) and its counterpart, Weak Effective Field Theory~(WEFT), below the electroweak scale. Starting from the WEFT Lagrangian, we compute the coefficients that modify neutrino production in meson decays and detection via deep-inelastic scattering, and we express the new physics effects in terms of modified flavor transition probabilities. For some coupling structures, we find that FASER$\nu$ will be able to constrain interactions that are two to three orders of magnitude weaker than Standard Model weak interactions, implying that the experiment will be indirectly probing new physics at the multi-TeV scale. In some cases, FASER$\nu$ constraints will become comparable to existing limits - some of them derived for the first time in this paper - already with $150~$fb${}^{-1}$ of data., Comment: 44 pages, 9 figures, 4 tables, 2 babies

We study the forward-backward asymmetry $A_{FB}$ in $pp \to \ell^+\ell^-$ at the Z peak within the Standard Model Effective Field Theory (SMEFT). We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks,which close a flat direction in the electroweak precision SMEFT fit. Moreover, we show that current $A_{FB}$ data is precise enough so that its inclusion in the fit improves significantly LEP bounds even in simple New Physics setups. This demonstrates that the LHC can compete with and complement LEP when it comes to precision measurements of the Z boson properties, Comment: 24 pages, 5 figures

Precision measurements in allowed nuclear beta decays and neutron decay are reviewed and analyzed both within the Standard Model and looking for new physics. The analysis incorporates the most recent experimental and theoretical developments. The results are interpreted in terms of Wilson coefficients describing the effective interactions between leptons and nucleons (or quarks) that are responsible for beta decay. New global fits are performed incorporating a comprehensive list of precision measurements in neutron decay, superallowed $0^+\rightarrow 0^+$ transitions, and other nuclear decays that include, for the first time, data from mirror beta transitions. The results confirm the $V$-$A$ character of the interaction and translate into updated values for $V_{ud}$ and $g_A$ at the $10^{-4}$ level. We also place new stringent limits on exotic couplings involving left-handed and right-handed neutrinos, which benefit significantly from the inclusion of mirror decays in the analysis., Comment: 35 pages; v2: analysis updated, comments and references added; v3: compared to the JHEP version, typos in Eqs. 2.1, A3, A4 corrected, Eq. 4.4 updated, comment on aCORN update added in footnote 12

Neutrino oscillations are precision probes of new physics beyond the Standard Model. Apart from neutrino masses and mixings, they are also sensitive to possible deviations of low-energy interactions between quarks and leptons from the Standard Model predictions. In this paper we develop a systematic description of such non-standard interactions (NSI) in oscillation experiments within the quantum field theory framework. We calculate the event rate and oscillation probability in the presence of general NSI, starting from the effective field theory (EFT) in which new physics modifies the flavor or Lorentz structure of charged-current interactions between leptons and quarks. We also provide the matching between the EFT Wilson coefficients and the widely used simplified quantum-mechanical approach, where new physics is encoded in a set of production and detection NSI parameters. Finally, we discuss the consistency conditions for the standard NSI approach to correctly reproduce the quantum field theory result., Comment: 23 pages; v2: minor changes, references added; v3: paper reorganized, new section on neutrinos from muon decay, appendix A improved

We study constraints on the Standard Model Effective Field Theory (SMEFT) from neutrino oscillations in short-baseline reactor experiments. We calculate the survival probability of reactors antineutrinos at the leading order in the SMEFT expansion, that is including linear effects of dimension-6 operators. It is shown that, at this order, reactor experiments alone cannot probe charged-current contact interactions between leptons and quarks that are of the (pseudo)vector (V$\pm$A) or pseudo-scalar type. We also note that flavor-diagonal (pseudo)vector coefficients do not have observable effects in oscillation experiments. In this we reach novel or different conclusions than prior analyses of non-standard neutrino interactions. On the other hand, reactor experiments offer a unique opportunity to probe tensor and scalar SMEFT operators that are off-diagonal in the lepton-flavor space. We derive constraints on the corresponding SMEFT parameters using the most recent data from the Daya Bay and RENO experiments., Comment: 36 pages, 6 figures. v2: corrected sign error in tensor contribution (d_T); references and comments added; discussion improved. v3: analysis improved, published version

The extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix from flavour observables can be affected by physics beyond the Standard Model (SM). We provide a general roadmap to take this into account, which we apply to the case of the Standard Model Effective Field Theory (SMEFT). We choose a set of four input observables that determine the four Wolfenstein parameters, and discuss how the effects of dimension-six operators can be included in their definition. We provide numerical values and confidence intervals for the CKM parameters, and compare them with the results of CKM fits obtained in the SM context. Our approach allows one to perform general SMEFT analyses in a consistent fashion, independently of any assumptions about the way new physics affects flavour observables. We discuss a few examples illustrating how our approach can be implemented in practice., Comment: 36 pages. Version published in JHEP

We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $\tau \to \pi\pi\nu_\tau$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent level. These bounds are complementary to the ones from electroweak precision observables and $p p \to \tau \nu_\tau$ measurements at the LHC. The combination of tau decay and LHC data puts tighter constraints on lepton universality violation in the gauge boson-lepton vertex corrections., Comment: 8 pages; v2: comments and references added, PRL version

The "golden" channel, in which the newly-discovered Higgs boson decays to four leptons by means of intermediate vector bosons, is important for determining the properties of the Higgs boson and for searching for subtle new physics effects. Different approaches exist for parametrizing the relevant Higgs couplings in this channel; here we relate the use of pseudo-observables to methods based on specifying the most general amplitude or Lagrangian terms for the $HVV$ interactions. We also provide projections for sensitivity in this channel in several novel scenarios, illustrating the use of pseudo-observables, and analyze the role of kinematic distributions and (ratios of) rates in such $H\to4\ell$ studies., Comment: 33 pages, 4 figures consisting of 9 panels. Added reference. Corresponds to version accepted by JHEP

The status of tests of the standard electroweak model and of searches for new physics in allowed nuclear $\beta$ decay and neutron decay is reviewed including both theoretical and experimental developments. The sensitivity and complementarity of recent and ongoing experiments are discussed with emphasis on their potential to look for new physics. Measurements are interpreted using a model-independent effective field theory approach enabling to recast the outcome of the analysis in many specific new physics models. Special attention is given to the connection that this approach establishes with high-energy physics. A new global fit of available $\beta$-decay data is performed incorporating, for the first time in a consistent way, superallowed $0^+\to 0^+$ transitions, neutron decay and nuclear decays. The constraints on exotic scalar and tensor couplings involving left- or right-handed neutrinos are determined while a constraint on the pseudoscalar coupling from neutron decay data is obtained for the first time as well. The values of the vector and axial-vector couplings, which are associated within the standard model to $V_{ud}$ and $g_A$ respectively, are also updated. The ratio between the axial and vector couplings obtained from the fit under standard model assumptions is $C_A/C_V = -1.27510(66)$. The relevance of the various experimental inputs and error sources is critically discussed and the impact of ongoing measurements is studied. The complementarity of the obtained bounds with other low- and high-energy probes is presented including ongoing searches at the Large Hadron Collider., Comment: 70 pages, 14 figures. Invited review article for Prog. Part. Nucl. Phys. v2: Journal version (clarifications, references, and 2 new figures added)

We compile information from low-energy observables sensitive to flavor-conserving 4-fermion operators with two or four leptons. Our analysis includes data from e+e- colliders, neutrino scattering on electron or nucleon targets, atomic parity violation, parity-violating electron scattering, and the decay of pions, neutrons, nuclei and tau leptons. We recast these data as tree-level constraints on 4-fermion operators in the Standard Model Effective Field Theory (SMEFT) where the SM Lagrangian is extended by dimension-6 operators. We allow all independent dimension-6 operators to be simultaneously present with an arbitrary flavor structure. The results are presented as a multi-dimensional likelihood function in the space of dimension-6 Wilson coefficients, which retains information about the correlations. In this form, the results can be readily used to place limits on masses and couplings in a large class of new physics theories., Comment: 39 pages; full correlation matrix and likelihood function available in Mathematica notebook at https://www.dropbox.com/s/26nh71oebm4o12k/SMEFTlikelihood.nb?dl=0 v2: comments and references added, translation to Warsaw basis provided in notebook; v3: references added

We study the renormalization group evolution (RGE) of new physics contributions to (semi)leptonic charged-current meson decays, focusing on operators involving a chirality flip at the quark level. We calculate their evolution under electroweak and electromagnetic interactions, including also the three-loop QCD running and provide numerical formulas that allow us to connect the values of the corresponding Wilson coefficients from scales at the TeV to the low-energy scales. The large mixing of the tensor operator into the (pseudo)scalar ones has important phenomenological implications, such as the RGE of new physics bounds obtained from light quark decays or in $b\to c\ell\nu$ transitions. For instance, we study scenarios involving tensor effective operators, which have been proposed in the literature to address the $B$-decay anomalies, most notably those concerning the $R_{D^{(*)}}$ ratios. We conclude that the loop effects are important and should be taken into account in the analysis of these processes, especially if the operators are generated at an energy scale of $\sim 1$ TeV or higher., Comment: v2 that matches published version

We discuss how to perform consistent extractions of anomalous triple gauge couplings (aTGC) from electroweak boson pair production at the LHC in the Standard Model Effective Field Theory (SMEFT). After recasting recent ATLAS and CMS searches in $pp\to WZ (WW) \to \ell' \nu \ell^+\ell^- (\nu_{\ell})$ channels, we find that: (a) working consistently at order $\Lambda^{-2}$ in the SMEFT expansion the existing aTGC bounds from Higgs and LEP-2 data are not improved, (b) the strong limits quoted by the experimental collaboration are due to the partial $\Lambda^{-4}$ corrections (dimension-6 squared contributions). Using helicity selection rule arguments we are able to explain the suppression in some of the interference terms, and discuss conditions on New Physics (NP) models that can benefit from such LHC analyses. Furthermore, standard analyses assume implicitly a quite large NP scale, an assumption that can be relaxed by imposing cuts on the underlying scale of the process ($\sqrt{\hat{s}}$). In practice, we find almost no correlation between $\sqrt{\hat{s}}$ and the experimentally accessible quantities, which complicates the SMEFT interpretation. Nevertheless, we provide a method to set (conservative) aTGC bounds in this situation, and recast the present searches accordingly. Finally, we introduce a simple NP model for aTGC to compare the bounds obtained directly in the model with those from the SMEFT analysis., Comment: 31 pages, 13 figures, 4 tables. Version to appear in JHEP

The current most stringent constraints on exotic scalar or tensor couplings in neutron and nuclear $\beta$ 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 $\beta$ 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 $\beta$ or the recoil energy spectrum. This observation is relevant for the selection of sensitive transitions in searches for exotic couplings through spectrum shape measurements. We then point out previous errors in the exploitation of measurements of the $\beta-\nu$ angular correlation coefficient and discuss their impact on the extraction of constraints on exotic couplings., Comment: 7 pages, 5 figures

We review a novel model-independent approach to the analysis of new-physics effects in the $s\to u\ell^-\bar\nu$ transitions. We apply it to (semi)leptonic kaon decays and study their complementarity with pion and hyperon $\beta$ decays or with collider searches of new physics., Comment: Contribution to the NA62 Physics Handbook. It summarizes the analysis presented in arXiv:1605.07114 and discusses in more detail the interplay between $K_{\mu3}$ and semileptonic hyperon decays as new-physics probes

We analyze the decays $K\to\pi\ell\nu$ and $P\to\ell\nu$ ($P=K,\pi$, $\ell=e,\,\mu$) using a low-energy Effective-Field-Theory approach to parametrize New Physics and study the complementarity with baryon $\beta$ decays. We then provide a road map for a global analysis of the experimental data, with all the Wilson coefficients simultaneously, and perform a fit leading to numerical bounds for them and for $V_{us}$. A prominent result of our analysis is a reinterpretation of the well-known $V_{ud}-V_{us}$ diagram as a strong constraint on new physics. Finally, we reinterpret our bounds in terms of the $SU(2)_L\times~U(1)_Y$-invariant operators, provide bounds to the corresponding Wilson coefficients at the TeV scale and compare our results with collider searches at the LHC., Comment: 45 pages, 4 figures; v2: minor changes to match version published in JHEP

We present a combined analysis of LHC Higgs data (signal strengths) together with LEP-2 WW production measurements. To characterize possible deviations from the Standard Model (SM) predictions, we employ the framework of an Effective Field Theory (EFT) where the SM is extended by higher-dimensional operators suppressed by the mass scale of new physics $\Lambda$. The analysis is performed consistently at the order $\Lambda^{-2}$ in the EFT expansion keeping all the relevant operators. While the two data sets suffer from flat directions, together they impose stringent model-independent constraints on the anomalous triple gauge couplings. As a side product, we provide the results of the combined fit in different EFT bases., Comment: 7 pages. v2: References and clarifications added

We analyze the bounds on the Higgs pseudo-observables following from electroweak constraints, under the assumption that the Higgs particle is the massive excitation of an $SU(2)_L$ doublet. Using such bounds, detailed predictions for $h\to 4\ell$ decay rates, dilepton spectra, and lepton-universality ratios are presented., Comment: 12 pages, 6 figures. Extended the discussion on the electroweak bounds to PO relevant for charged current Higgs decays. References added

We evaluate the impact of recent developments in hadron phenomenology on extracting possible fundamental tensor interactions beyond the standard model. We show that a novel class of observables, including the chiral-odd generalized parton distributions, and the transversity parton distribution function can contribute to the constraints on this quantity. Experimental extractions of the tensor hadronic matrix elements, if sufficiently precise, will provide a so far absent testing ground for lattice QCD calculations., Comment: 5 pages, 2 figures

We investigate the discovery potential of semileptonic hyperon decays in terms of searches of new physics at teraelectronvolt scales. These decays are controlled by a small $SU(3)$-flavor breaking parameter that allows for systematic expansions and accurate predictions in terms of a reduced dependence on hadronic form factors. We find that muonic modes are very sensitive to non-standard scalar and tensor contributions and demonstrate that these could provide a powerful synergy with direct searches of new physics at the LHC., Comment: v2. Comparison with direct searches of new physics at the LHC presented

We define a set of pseudo-observables characterizing the properties of Higgs decays in generic extensions of the Standard Model with no new particles below the Higgs mass. The pseudo-observables can be determined from experimental data, providing a systematic generalization of the "kappa-framework" so far adopted by the LHC experiments. The pseudo-observables are defined from on-shell decay amplitudes, allow for a systematic inclusion of higher-order QED and QCD corrections, and can be computed in any Effective Field Theory (EFT) approach to Higgs physics. We analyze the reduction of the number of independent pseudo-observables following from the hypotheses of lepton-universality, CP invariance, custodial symmetry, and linearly realized electroweak symmetry breaking. We outline the importance of kinematical studies of $h\to 4\ell$ decays for the extraction of such parameters and present their predictions in the linear EFT framework., Comment: 34 pages, 3 figures (v2: extended discussions on the validity of the approach; minor typos corrected. Published version)

Different aspects of Tau physics are discussed, both as a New Physics probe and as a tool to study Standard Model physics. The goal of this Tau2014 opening talk is to introduce (some of) the many research directions currently being pursued with tau leptons, which will be discussed in great technical detail in the following talks., Comment: Written version of the Opening Talk at the 13th International Workshop on Tau Lepton Physics (TAU2014), Sept 2014, Aachen, Germany

We analyze $h\to 4\ell$ decays in the kinematical region where the dilepton pair of low invariant mass ($m_{34}$) is not far from QCD resonances ($\Psi$ and $\Upsilon$ states). On the one hand, we present precise predictions of the spectrum within the Standard Model, taking into account non-perturbative QCD effects. On the other hand, we illustrate the sensitivity of this spectrum to New Physics models predicting the existence of new exotic light states. In particular, we show that parameter regions of models relevant to explain the $(g-2)_\mu$ anomaly could be probed in the future by means of $h\to 4\ell$ decays., Comment: 14 pages, 3 figures (v2: minor modifications - published version)

We discuss the consequences of the approximate conservation of the vector and axial currents for the hadronic matrix elements appearing in beta decay if non-standard interactions are present. In particular the isovector (pseudo)scalar charge g_S(P) of the nucleon can be related to the difference (sum) of the nucleon masses in the absence of electromagnetic effects. Using recent determinations of these quantities from phenomenological and lattice QCD studies we obtain the accurate values g_S=1.02(11) and g_P=349(9) in the MS-bar scheme at mu=2 GeV. The consequences for searches of non-standard scalar interactions in nuclear beta decays are studied, finding epsilon_S=0.0012(24) at 90%CL, which is significantly more stringent than current LHC bounds and previous low-energy bounds using less precise g_S values. We argue that our results could be rapidly improved with updated computations and the direct calculation of certain ratios in lattice QCD. Finally we discuss the pion-pole enhancement of g_P, which makes beta decays much more sensitive to non-standard pseudoscalar interactions than previously thought., Comment: 6 pages, 2 figures

Precision measurements in nuclear beta decay offer a sensitive window to search for new physics beyond the standard electroweak model and allow also the determination of the fundamental weak vector coupling in processes involving the lightest quarks. Searches for new physics are also a strong motivation for experiments carried out at the high energy frontier reached at the most powerful particle colliders. It is instructive to confront results from the low energy and the high energy frontiers in order to look for possible complementarities and orient new avenues for experiments at low energies. We review here the status of constraints on new physics obtained from nuclear and neutron decays and compare them to those from other semi-leptonic processes and from the LHC. We stress the requirements of new precision experiments in beta decay in order to impact the search for new physics at the light of current and projected LHC results. We describe recent experimental results and ongoing developments in nuclear and neutron beta decay, with emphasis on their planned goals to improve present limits on exotic weak couplings., Comment: Submitted to Annalen der Physik for the Special Issue "Precision experiments and fundamental physics at low energies"

It is well known that semileptonic decays of light hadrons and nuclei can be used not only to determine the CKM element V_ud with high accuracy, but also as probes of physics beyond the Standard Model. In this talk I review recent works that studied this within an Effective Field Theory framework, comparing the sensitivity of different low-energy and LHC observables. A clear complementarity between low- and high-energy searches it is found., Comment: Proceedings of CKM 2012, the 7th International Workshop on the CKM Unitarity Triangle, University of Cincinnati, USA, 28 September - 2 October 2012

We study the impact of a leptophobic Z' gauge boson on the C_{1q} and C_{2q} 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'\bar{u}q (q=u,c,t) and Z'\bar{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 non-diagonal 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 explained the CDF W plus di-jet 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., Comment: 6 pages, 5 figures

We 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 beta 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., Comment: 18 pages, 2 figures

In this talk I review the New Physics reach of semileptonic beta decay experiments, and their interplay with LHC searches. Assuming the new particles are heavy enough we can use an Effective Field Theory approach to analyze the LHC searches, what allows us to perform a direct and model-independent comparison with low-energy experiments., Comment: Proceedings of CIPANP 2012 (3 pages)

The seeming violation of universality in the tau 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) x 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., Comment: 9 pages, 2 figures

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., Comment: 58 pages, 14 figures

In this article we present a simple theoretical framework where the origin of the mu-term and the matter-parity violating interactions of the minimal supersymmetric standard model can be understood from the spontaneous breaking of new Abelian gauge symmetries. In this context the masses of the Z' gauge bosons, the M-parity violating scale and the mu-term are determined by the supersymmetry breaking scale. The full spectrum of the theory is discussed in detail. We investigate the predictions for the Higgs masses in detail showing that it is possible to satisfy the LEP2 bounds even with sub-TeV squark masses. The model predicts the existence of light colored fields, lepton and baryon number violation, and new neutral gauge bosons at the Large Hadron Collider., Comment: 14 pp. Minor corrections, to appear in Physical Review D

Using an effective field theory approach, we study the new physics (NP) corrections to muon and beta decays and their effects on the extractions of V_ud and V_us. Assuming nearly flavor blind NP interactions we find that the CKM-unitarity test is the only way to expose NP. The four short-distance operators that can generate a deviation are strongly constrained by the phenomenological bound |Vud|^2 + |Vus|^2 + |Vub|^2 - 1 = (-0.0001 \pm 0.0006), corresponding to an effective scale > 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better than that generated by the Z pole observables., Comment: To appear in the proceedings of the 45th Rencontres de Moriond: Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 6-13 Mar 2010

We analyse the so-called violations of quark-hadron duality in Finite Energy Sum Rules with the LR correlator, through the study of the possible high-energy behavior of the LR spectral function, taking into account all known short-distance constraints and the experimental tau-decay data. In particular we show that the use of pinched weights allows to determine with high accuracy the dimension six and eight contributions in the Operator-Product Expansion, O_6 = (-4.3^{+0.9}_{-0.7}) 10^{-3} GeV^6 and O_8 = (-7.2^{+4.2}_{-5.3}) 10^{-3} GeV^8., Comment: Talk given at the 15th International QCD Conference (Montpellier, 28th June - 3rd July 2010) and the Internation Light Cone 2010 Conference (Valencia, 14-18th June 2010)

We analyze the so-called pinched weights, that are generally thought to reduce the violation of quark-hadron duality in Finite-Energy Sum Rules. After showing how this is not true in general, we explain how to address this question for the LR correlator and any particular pinched weight taking advantage of our previous work [1], where the possible high-energy behavior of the LR spectral function was studied. In particular we show that the use of pinched weights allows to determine with high accuracy the dimension six and eight contributions in the operator product expansion, O6=(-4.3^[+0.9}_{-0.7})*10^-3 GeV^6 and O8=(-7.2^{+4.2}_{-5.3})*10^-3 GeV^8., Comment: 11 pages. A few references added and discussion slightly enlarged. Results unchanged.

We analyze the spectral moments of the V-A two-point correlation function. Using all known short-distance constraints and the most recent experimental data from tau decays, we determine the lowest spectral moments, trying to assess the uncertainties associated with the so-called violations of quark-hadron duality. We have generated a large number of "acceptable" spectral functions, satisfying all conditions, and have used them to extract the wanted hadronic parameters through a careful statistical analysis. We obtain accurate values for the ChPT couplings L10 and C87, and a realistic determination of the dimension six and eight contributions in the operator product expansion, O6=(-5.4^{+3.6}_{-1.6})*10^-3 GeV^6 and O8=(-8.9^{+12.6}_{-7.4})*10^-3 GeV^8, showing that the duality-violation effects have been usually underestimated in previous literature., Comment: 17 pp, slightly modified version to be published in PRD.

Through an effective field theory approach, we analyze the new physics corrections to muon and beta decays and their effects on the extractions of V_ud and V_us. Assuming nearly flavor blind NP interactions, we find that the only quantity sensitive to NP is Delta_CKM = |V_ud|^2 + |V_us|^2 + |V_ub|^2 - 1, that receives contributions from four short distance operators. The phenomenological bound Delta_CKM = (-1 \pm 6) 10^-4 provides strong constraints on all four operators, corresponding to an effective scale Lambda > 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better than that generated by the Z pole observables., Comment: Talk given at the FLAVIAnet topical workshop 'Low energy constraints on extensions of the Standard Model' (Kazimierz, Poland), July 2009. 6 pages

We describe non-standard contributions to semileptonic processes in a model independent way in terms of an SU(2)_L X U(1)_Y invariant effective lagrangian at the weak scale, from which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, \Delta_CKM = |V_ud|^2 + |V_us|^2 + |V_ub|^2 - 1, receives contributions from four effective operators. The phenomenological bound of \Delta_CKM = -1E-4 +- 6E-4 provides strong constraints on all four operators, corresponding to an effective scale greater than 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better then the Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as \Delta_CKM = -0.01 (90% CL). An observed nonzero \Delta_CKM at this level could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements., Comment: 23 pages, 1 table and 5 eps figures

Using recent precise hadronic tau-decay data on the V-A 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_10 and C_87. At order p^4 we obtain L_10^r(M_rho)=-(5.22+-0.06)10^-3, whereas at order p^6 we get L_10^r(M_rho)=-(4.06+-0.39)10^-3 and C_87^r(M_rho) = (4.89+-0.19)10^-3 GeV^-2., Comment: 4 pages, 2 figures. Included in the proceedings of the 14th International QCD Conference, July 2008 Montpellier (France)

Using recent precise hadronic tau-decay data on the V-A 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_10^r(M_rho) and C_87^r(M_rho). These two low-energy constants appear at order p^4 and p^6, respectively, in the chiral perturbation theory expansion of the V-A correlator. At order p^4 we obtain L_10^r(M_rho) = -(5.22\pm 0.06)10^{-3}. Including in the analysis the two-loop (order p^6) contributions, we get L_10^r(M_rho) = -(4.06\pm 0.39)10^{-3} and C_87^r(M_rho) = (4.89\pm 0.19)10^{-3}GeV^{-2}. In the SU(2) chiral effective theory, the corresponding low-energy coupling takes the value \overline l_5 = 13.30 \pm 0.11 at order p^4, and \overline l_5 = 12.24 \pm 0.21 at order p^6., Comment: 17 pages, 3 figures, v2: Added reference, published version