arXiv subjects

D. Meloni

Publications and source records attributed to D. Meloni.

At least 37 records · Page 2Linked to original sources

arXiv2014

Perturbative and non-perturbative renormalization results of the Chromomagnetic Operator on the Lattice

The Chromomagnetic operator (CMO) mixes with a large number of operators under renormalization. We identify which operators can mix with the CMO, at the quantum level. Even in dimensional regularization (DR), which has the simplest mixing pattern, the CMO mixes with a total of 9 other operators, forming a basis of dimension-five, Lorentz scalar operators with the same flavor content as the CMO. Among them, there are also gauge noninvariant operators; these are BRST invariant and vanish by the equations of motion, as required by renormalization theory. On the other hand using a lattice regularization further operators with $d \leq 5$ will mix; choosing the lattice action in a manner as to preserve certain discrete symmetries, a minimul set of 3 additional operators (all with $d<5$) will appear. In order to compute all relevant mixing coefficients, we calculate the quark-antiquark (2-pt) and the quark-antiquark-gluon (3-pt) Green's functions of the CMO at nonzero quark masses. These calculations were performed in the continuum (dimensional regularization) and on the lattice using the maximally twisted mass fermion action and the Symanzik improved gluon action. In parallel, non-perturbative measurements of the $K-π$ matrix element are being performed in simulations with 4 dynamical ($N_f = 2+1+1$) twisted mass fermions and the Iwasaki improved gluon action.

hep-lat↗

arXiv2014

K -> pi matrix elements of the chromagnetic operator on the lattice

We present preliminary results of the first lattice QCD calculation of the K -> pi matrix elements of the chromomagnetic operator O_{CM}=g sbar sigma_{munu} G_{munu} d, which appears in the effective Hamiltonian describing Delta S=1 transitions in and beyond the Standard Model. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with operators of equal and lower dimensionality. The multiplicative renormalization factor as well as the mixing coefficients with the operators of equal dimension have been computed at one-loop in perturbation theory. The power divergent coefficients controlling the mixing with operators of lower dimension have been computed non-perturbatively, by imposing suitable subtraction conditions. The numerical simulations have been carried out using the gauge field configurations produced by the European Twisted Mass Collaboration with N_f=2+1+1 dynamical quarks at three values of the lattice spacing. Our preliminary result for the B-parameter of the chromomagnetic operator is B_{CMO}=0.29(11), which can be compared with the estimate B_{CMO}~1-4 currently used in phenomenological analyses.

hep-lat↗

arXiv2014

The Daya Bay and T2K results on $\sin^2 2 θ_{13}$ and Non-Standard Neutrino Interactions

We show that the relatively large best fit value of $\sin^2 2 θ_{13} = 0.14 \, (0.17)$ measured in the T2K experiment for fixed values of i) the Dirac CP violation phase $δ= 0$, and ii) the atmospheric neutrino mixing parameters $θ_{23} = π/4$, $|Δm^2_{32}| = 2.4 \times 10^{-3} \; {\rm eV}^2$, can be reconciled with the Daya Bay result $\sin^2 2 θ_{13} = 0.090 \pm 0.009$ if the effects of non-standard neutrino interactions (NSI) in the relevant $\bar ν_e \to \bar ν_e$ and $ν_μ\to ν_e$ oscillation probabilities are taken into account.

hep-ph↗

arXiv2014

Constraining new physics scenarios in neutrino oscillations from Daya Bay data

We perform for the first time a detailed fit to the $\bar ν_e \to \bar ν_e$ disappearance data of the Daya Bay experiment to constrain the parameter space of models where sterile neutrinos can propagate in a large compactified extra dimension (LED) and models where non-standard interactions affect the neutrino production and detection (NSI). We find that the compactification radius $R$ in LED scenarios can be constrained at the level of $0.57 \, μm$ for normal ordering and of $0.19\, μm$ for inverted ordering, at 2$σ$ confidence level. For the NSI model, reactor data put a strong upper bound on the parameter $\varepsilon_{ee}$ at the level of $\sim 10^{-3}$, whereas the main effect of $\varepsilon_{eμ}$ and $\varepsilon_{eτ}$ is a worsening of the determination of $θ_{13}$.

hep-ph↗

arXiv2014

Two-zero Majorana textures in the light of the Planck results

The recent results of the Planck experiment put a stringent constraint on the sum of the light neutrino masses, m1+m2+m3 < 0.23 eV (95 % CL). On the other hand, two-zero Majorana mass matrix textures predict strong correlations among the atmospheric angle and the sum of the masses. We use the Planck result to show that, for the normal hierarchy case, the texture with vanishing (2,2) and (3,3) elements is ruled out at a high confidence level; in addition, we emphasize that a future measurement of the octant of the atmospheric mixing angle (or the one sigma determination of it based on recent fit to neutrino data) will put severe constraint on the possible structure of the Majorana mass matrix. The implication of the above mentioned correlations for neutrinoless double beta-decay are also discussed, for both normal and inverted orderings.

hep-ph↗

arXiv2013

The chromomagnetic operator on the lattice

We study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangeness-changing effective Hamiltonian which describes electroweak effects in the Standard Model and beyond. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality, including also non gauge invariant quantities; it is thus quite a challenge to extract from lattice simulations a clear signal for the hadronic matrix elements of this operator. We compute all relevant mixing coefficients to one loop in lattice perturbation theory; this necessitates calculating both 2-point (quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. For a comprehensive presentation of our results, along with detailed explanations and a more complete list of references, we refer to our forthcoming publication [1].

hep-lat↗

arXiv2012

Fine-tuning and naturalness issues in the two-zero neutrino mass textures

In this paper we analyze the compatibility of two-zero neutrino Majorana textures with the recent experimental data. Differently from previous works, we use the experimental data to fix the values of the non-vanishing mass matrix entries and study in detail the correlations and degree of fine-tuning among them, which is also a measure of how naturally a given texture is able to describe all neutrino data. This information is then used to expand the textures in powers of the Cabibbo angle; extracting random O(1) coefficients, we show that only in few cases such textures reproduce the mixing parameters in their 3 sigma ranges.

hep-ph↗

arXiv2012

Revisiting the T2K data using different models for the neutrino-nucleus cross sections

We present a three-flavour fit to the recent νμ--> νe and νμ--> νμT2K oscillation data with different models for the neutrino-nucleus cross section. We show that, even for a limited statistics, the allowed regions and best fit points in the (θ_{13},δ_{CP}) and (θ_{23},Δm^2_{atm}) planes are affected if, instead of using the Fermi Gas model to describe the quasielastic cross section, we employ a model including the multinucleon emission channel.

hep-ph↗

arXiv2012

EUROnu-WP6 2010 Report

This is a summary of the work done by the Working Package 6 (Physics) of the EU project "EUROnu" during the second year of activity of the project.

hep-ph↗

arXiv2012

D14 - A Common Origin of the Cabibbo Angle and the Lepton Mixing Angle theta^l_13

It has been shown that the Cabibbo angle can be predicted in terms of group theoretical quantities, if the dihedral group D14 plays the role of a flavor symmetry. We extend a supersymmetric D14 model to the lepton sector and show that theta^nu_13 and the deviation of theta^nu_23 from maximal mixing in the neutrino sector originate, similar to the Cabibbo angle in the quark sector, from a mismatch of different subgroups of D14 and are of the size of the Cabibbo angle. The mixing angles in the charged lepton sector are small. Thus, the lepton mixing angle theta^l_13 is naturally in its experimentally preferred range and theta^l_23 within its 3 sigma range. The solar mixing angle is of order one and the charged lepton mass hierarchy is correctly reproduced. Leading order results are only slightly perturbed, if next-to-leading order corrections are taken into account.

hep-ph↗

arXiv2012

Predicting leptonic CP violation in the light of Daya Bay result

In the light of the recent Daya Bay result the reactor angle is about 9 degrees, we reconsider the model presented in arXiv:1005.3482 showing that, when all neutrino oscillation parameters are taken at their best fit values of Schwetz et al and the reactor angle to be the central value of Daya Bay, the predicted value of the CP phase is approximately 45 degrees.

hep-ph↗

arXiv2012

Proceedings of the first workshop on Flavor Symmetries and consequences in Accelerators and Cosmology (FLASY2011)

The main goals of the first "Workshop on FLAvor SYmmetries and consequences in accelerators and cosmology" (FLASY) was to summarize the theoretical status of flavor symmetries, bringing together young researchers in the field to stimulate discussions and new collaborations, with the aim of investigating possible new physics scenarios to be tested at the LHC, as well as in future neutrino, cosmology experiments and dark matter searches.

hep-ph↗

arXiv2011

Interim Design Report

The International Design Study for the Neutrino Factory (the IDS-NF) was established by the community at the ninth "International Workshop on Neutrino Factories, super-beams, and beta- beams" which was held in Okayama in August 2007. The IDS-NF mandate is to deliver the Reference Design Report (RDR) for the facility on the timescale of 2012/13. In addition, the mandate for the study [3] requires an Interim Design Report to be delivered midway through the project as a step on the way to the RDR. This document, the IDR, has two functions: it marks the point in the IDS-NF at which the emphasis turns to the engineering studies required to deliver the RDR and it documents baseline concepts for the accelerator complex, the neutrino detectors, and the instrumentation systems. The IDS-NF is, in essence, a site-independent study. Example sites, CERN, FNAL, and RAL, have been identified to allow site-specific issues to be addressed in the cost analysis that will be presented in the RDR. The choice of example sites should not be interpreted as implying a preferred choice of site for the facility.

hep-ex↗

arXiv2011

Constraining neutrinoless double beta decay

A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.

hep-ph↗

arXiv2011

Stability of dark matter from the D4xZ2 flavor group

We study a model based on the dihedral group D4 in which the dark matter is stabilized by the interplay between a remnant Z2 symmetry, of the same spontaneously broken non-abelian group, and an auxiliary Z2 introduced to eliminate unwanted couplings in the scalar potential. In the lepton sector the model is compatible with normal hierarchy only and predicts a vanishing reactor mixing angle. Since m1=0, we also have a simple prediction for the effective mass in terms of the solar angle. There also exists a large portion of the model parameter space where the upper bounds on lepton flavor violating processes are not violated. We incorporate quarks in the same scheme finding that a description of the CKM mixing matrix is possible and that semileptonic K and D decays mediated by flavour changing neutral currents are under control.

hep-ph↗

arXiv2011

The $τ$-contamination of the golden muon sample at the Neutrino Factory

We study the contribution of $ν_e \to ν_τ\to τ\to μ$ transitions to the wrong-sign muon sample of the {\em golden} channel of the Neutrino Factory. Muons from tau decays are not really a background, since they contain information from the oscillation signal, and represent a small fraction of the sample. However, if not properly handled they introduce serious systematic error, in particular if the detector/analysis are sensitive to muons of low energy. This systematic effect is particularly troublesome for large $θ_{13} \geq 1^\circ$ and prevents the use of the Neutrino Factory as a precision facility for large $θ_{13}$. Such systematic error disappears if the tau contribution to the golden muon sample is taken into account. The fact that the fluxes of the Neutrino Factory are exactly calculable permits the knowledge of the tau sample due to the $ν_e \to ν_τ$ oscillation. We then compute the contribution to the muon sample arising from this sample {\em in terms of the apparent muon energy}. This requires the computation of a migration matrix $M_{ij}$ which describes the contributions of the tau neutrinos of a given energy $E_i$, to the muon neutrinos of an apparent energy $E_j$. We demonstrate that applying $M_{ij}$ to the data permits the full correction of the otherwise intolerable systematic error.

hep-ph↗

arXiv2011

Neutrino phenomenology and stable dark matter with A4

We present a model based on the A4 non-abelian discrete symmetry leading to a predictive five-parameter neutrino mass matrix and providing a stable dark matter candidate. We found an interesting correlation among the atmospheric and the reactor angles which predicts theta_23 ~ pi/4 for very small reactor angle and deviation from maximal atmospheric mixing for large theta_13. Only normal neutrino mass spectrum is possible and the effective mass entering the neutrinoless double beta decay rate is constrained to be |m_ee| > 4 10^{-4} eV.

hep-ph↗

arXiv2010

Fritzsch neutrino mass matrix from S3 symmetry

We present an extension of the Standard Model (SM) based on the discrete flavor symmetry S3 which gives a neutrino mass matrix with two-zero texture of Fritzsch-type and nearly diagonal charged lepton mass matrix. The model is compatible with the normal hierarchy only and predicts the sine squared of the reactor angle to be 0.01 at the best fit values of solar and atmospheric parameters and maximal leptonic CP violation.

hep-ph↗