Search

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., 55 pages; V2: corrected tensor matrix element, discussion of matrix elements expanded in Appendix A

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 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 analyze h→4ℓ decays in the kinematical region where the dilepton pair of low invariant mass ( m34 ) is not far from QCD resonances ( Ψ and ϒ 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)μ anomaly could be probed in the future by means of h→4ℓ decays.

184 páginas. Tesis Doctoral del Departamento de Física Teórica, de la Universidad de Valencia, y del Instituto de Física Corpuscular (IFIC). Fecha de lectura: 07-09-2010, En esta tesis se analizan dos aspectos diversos de la Física de Partículas a nivel teórico. En primer lugar se estudian las reglas de suma de la Cromodinámica Cuántica (QCD) como técnica que permite obtener predicciones hadrónicas a partir de las ecuaciones fundamentales de QCD, prestando una especial atención a la contribución que tiene su orígen en la violación de la dualidad quark-hadrón. En particular se aplica esta técnica para extraer, a partir de los datos de las desintegraciones hadrónicas del leptón tau, los parámetros quirales L10 y C87 y las distintas contribuciones a la OPE del correlador LR. Por otra parte, en esta tesis se analizan los efectos debidos a nueva física en observables de energías bajas en el marco teórico que nos proporcionan las teorías de campo efectivas. Se estudian las posibles estructuras de sabor de la nueva teoría y se analiza qué información puede extraerse en cada caso de las medidas de precisión realizadas hasta la fecha en experimentos de sabor (con kaones, piones, tau, ...).

Comunicación presentada en Topical Workshop on Low Energy Constraints on Extensions of the Standard Model. Kazimierz (POLAND). JUL 23-27, 2009, Through an effective field theory approach, we analyse the new physics (NP) corrections to muon and beta decays and their effects on the extractions of V(ud) and V(us). Assuming nearly flavour blind NP interactions, we find that the only quantity sensitive to NP is Delta(CKM) equivalent to vertical bar V(ud)vertical bar(2) + vertical bar V(us)vertical bar(2) + vertical bar V(ub)vertical bar(2) - 1, that receives contributions from four short distance operators. The phenomenological bound Delta(CKM) = (-1 +/- 6) x 10(-4) provides strong constraints on all four operators, corresponding to an effective scale Lambda > 11 TeV (90% C.L.). Depending on the operator, this constraint is at the same level or better than that generated by the Z pole observables.

7 páginas, 3 figuras.-- PACS numbers: 13.35.Dx, 11.55.Hx, 12.39.Fe, Using recent precise hadronic τ-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 L10r(Mρ) and C87r(Mρ). These two low-energy constants appear at order p4 and p6, respectively, in the chiral perturbation theory expansion of the V-A correlator. At order p4 we obtain L10r(Mρ)=-(5.22±0.06)×10-3. Including in the analysis the two-loop (order p6) contributions, we get L10r(Mρ)=-(4.06±0.39)×10-3 and C87r(Mρ)=(4.89±0.19)×10-3 GeV-2. In the SU(2) chiral effective theory, the corresponding low-energy coupling takes the value l̅ 5=13.30±0.11 at order p4, and l̅ 5=12.24±0.21 at order p6., The work of M. G.-A. is supported by an FPU Grant (MICINN, Spain). This work has been supported in part by the EU RTN network FLAVIAnet [Contract No. MRTN-CT-2006-035482], by MICINN, Spain [Grants No. FPA2007-60323 (M. G.-A., A. P.), No. FPA2006-05294 (J. P.), and Consolider-Ingenio 2010 Programme No. CSD2007-00042-CPAN-] and by Junta de Andalucía (J. P.) [Grants No. P05-FQM 101, No. P05-FQM 467, and No. P07-FQM 03048].

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., 17 pages, 3 figures, v2: Added reference, published version

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

In the Standard Model of Particle Physics, which gives a very precise description of nature at many different scales, hadronic tau decays occur through the interaction of two weak charged currents mediated by the W boson, so it becomes a very nice test of electroweak interactions. On the other hand, the quark current is responsible for a hadronic continuum, which allows to study strong interactions in the nonperturbative regime. In this thesis, some of the most powerful methods, such as the Operator Product Expansion (OPE) in the vacuum, effective field theories, dispersion relations or chiral perturbation theory have used for different phenomenological applications. The first application is the study of the extraction of physical parameters from the V-A spectral function. Using data provided by the ALEPH collaboration, we have obtained some LECs from Chiral Perturbation Theory and information on vacuum condensates. The V+A spectral function allows one of the most precise determination of the strong coupling. We have made a comprehensive analysis using ALEPH data, critically reviewing the strategies used in previous works and putting forward various approaches which allow to study complementary aspects of the problem. Our final result is in agreement with the PDG value. In the chiral limit, one can relate vacuum condensates to the electroweak penguin contribution of K → $\pi$$\pi$ processes, key for a better understanding of CP violation in kaons. We use those relations to find an updated value for the Q8 matrix element using the updated ALEPH V-A spectral function. Alternatively, we use those relations in the opposite direction to get an inclusive determination of the pion decay constant and an updated value for a D=8 condensate. Finally, we study the sensitivity of hadronic tau decays to physics beyond the Standard Model in the electroweak sector in the model independent framework of the Standard Model as Effective Field Theory. When integrating out the heavy particles of the SM, one have at first order in New Physics 5 new couplings for the nonstrange sector. Combining information from exclusive and inclusive observables, we are able to set competitive bounds for all of them. We compare with information that can be obtained from other Electroweak Precision Observables and LHC ones. We also make an exploratory study of the non-strange sector. En el Modelo Estándar de Física de Partículas, que da una descripción muy precisa de la naturaleza a escalas energéticas muy diferentes, las desintegraciones hadrónicas ocurren a través de la interacción de dos corrientes débiles cargadas mediadas por un bosón W, lo que la convierte en una ventana a las interacciones electrodébiles. Por otro lado, la corriente de quarks es responsable de la aparición de un contínuo hadrónico que permite estudiar interacciones fuertes en el régimen no perturbativo. En esta tesis, algunos de los métodos con mayor potencial, como la expansión en producto de operadores en el vacío, teorías cuánticas de campos efectivas, relaciones de dispersión o teoría quiral de perturbaciones, son utilizados para diferentes aplicaciones fenomenológicas.Usando la última actualización de la función espectral V-A (no extraña) provista por la colaboración ALEPH, hemos obtenido valores actualizados para algunas de las constantes de acoplamiento de baja energía de teoría quiral de perturbaciones e información acerca de condensados en el vacío. Para ello, se han utilizado diferentes estrategias para reducir y estimar incertidumbres debidas a violaciones de dualidad. Hemos encontrado resultados en buen acuerdo con los que pueden encontrarse en la literatura.Mientras que la función espectral V-A nos provee con una información valiosa acerca de interacciones fuertes en regímenes no perturbativos, la función espectral V+A nos permite una determinación de la constante de acoplamiento fuerte muy precisa. Hemos realizado un análisis utilizando, de nuevo, datos provistos por la colaboración ALEPH, haciendo una revisión crítica de las estrategias usadas en trabajos previos y proponiendo varias alternativas y tests adicionales que permiten estudiar aspectos complementarios del problema. Nuestro resultado final está en muy buen acuerdo con el valor del ajuste global dado por el PDG.En el límite quiral, uno puede relacionar condensados en el vacío con elementos de matriz asociados a pingüinos electrodébiles de procesos K->pipi, algunos de los cuales son clave para entender la violación de la simetría CP en kaones. Explotando dichas relaciones, encontramos un valor (preliminar) actualizado para uno de esos elementos de matriz, Q8, usando de nuevo datos de la función espectral V-A. Dicho valor está en buen acuerdo con el valor obtenido por simulaciones en redes discretas. Alternativamente, uno puedo tomar dicho valor para aprender sobre condensados en el vacío y así obtener determinaciones más precisas basadas en desintegraciones hadrónicas de taus.Finalmente, en el último trabajo optamos por tomar una perspectiva distinta. En lugar de utilizar las desintegraciones hadrónicas del tau para aprender sobre QCD, en este trabajo tomamos los inputs de QCD de otros sectores y estudiar la sensibilidad a nueva física en el sector electrodébil. En lugar de trabajar en un modelo concreto, trabajamos en el marco de modelo estándar como teoría efectiva. Cuando integramos los grados de libertad pesados del modelo estándar, aparecen 5 nuevos acoplamientos en el sector no extraño. Combinando información sobre observables inclusivos y exclusivos, somos capaces de establecer restricciones competitivas para todos ellos. También llevamos a cabo una comparativa con otros observables electrodébiles de precisión y de LHC. Por último realizamos un estudio exploratorio del sector no extraño

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