arXiv subjects

M. Napsuciale

Publications and source records attributed to M. Napsuciale.

At least 37 records · Page 2Linked to original sources

arXiv2013

A Fourth Neutrino and its Consequences on CP Asymmetries

A general analysis of the consequences of including a fourth neutrino in the standard model matter content, on CP violating observables at neutrino oscillation experiments, is presented. Neutrino oscillations in vacuum and with matter effects are studied. For the former we update and generalize previous studies on CP asymmetries with an additional active neutrino using an updated fit of the PMNS mixing matrix. We study the values of the new CP violating phases which maximize the different CP asymmetries in T2K and MINOS-like setups aiming to elucidate if the new phases yield measurable effects in the most favorable case. We show that due to a combined effect of kinematics and unitarity it is possible to obtain an observable asymmetry in the survival channels without violating CPT. For the MINOS-like setup, we find maximum asymmetries in vacuum of the order of 2% and 4% for the $ν_μ\to ν_e$ and $ν_e \to ν_τ$ channels respectively. For the T2K-like setup we obtain maximum asymmetries of the order of 6% in the survival $ν_μ\to ν_μ$ channel. Tree level matter effects enhance the former reaching asymmetries of the order of 10% for the $ν_μ\to ν_e$ and $ν_e \to ν_τ$ channels, while the $ν_μ\to ν_μ$ survival channel changes slightly depending on the mass hierarchy. Box diagrams with the fourth mass eigenstate as a virtual particle were also considered, the corrections to the scattering amplitude being negligible.

hep-ph↗

arXiv2012

Electromagnetic multipole moments of elementary spin-1/2, 1, and 3/2 particles

We study multipole decompositions of the electromagnetic currents of spin-1/2, 1, and 3/2 particles described in terms of Lagrangians designed to reproduce representation specific wave equations which are second order in the momenta and which emerge within the recently elaborated Poincaré covariant projector method. We calculate the electric multipoles of the above spins for the spinor, the four-vector, and the four-vector--spinor representations, attend to the most general non-Lagrangian spin-3/2 currents which are allowed by Lorentz invariance to be of third order in the momenta and construct the linear current equivalent of identical multipole moments of one of them. We conclude that such non-Lagrangian currents are not necessarily more general than the two-term currents emerging within the covariant projector method. We compare our results with those of the conventional Proca-, and Rarita-Schwinger frameworks. Finally, we test the representation dependence of the multipoles by placing spin-1 and spin-3/2 in the respective (1,0)$\oplus$(0,1), and (3/2,0)$\oplus$(0,3/2) single-spin representations. We observe representation independence of the charge monopoles and the magnetic dipoles, in contrast to the higher multipoles, which turn out to be representation dependent. In particular, we find the bi-vector $(1,0)\oplus (0,1)$ to be characterized by an electric quadrupole moment of opposite sign to the one found in $(1/2,1/2)$, and consequently, to the $W$ boson. Our finding points toward the possibility that the $ρ$ meson could transform as part of an antisymmetric tensor with an $a_{1}$ meson-like state as its representation companion.

hep-ph↗

arXiv2011

On the sensitivity of the HAWC observatory to gamma-ray bursts

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles.

astro-ph.HE↗

arXiv2011

Dynamical Symmetry Breaking With a Fourth Generation

Adding a fourth generation to the Standard Model and assuming it to be valid up to some cutoff Λ, we show that electroweak symmetry is broken by radiative corrections due to the fourth generation. The effects of the fourth generation are isolated using a Lagrangian with a genuine scalar without self-interactions at the classical level. For masses of the fourth generation consistent with electroweak precision data (including the B \rightarrow K π CP asymmetries) we obtain a Higgs mass of the order of a few hundreds GeV and a cutoff Λ around 1-2 TeV. We study the reliability of the perturbative treatment used to obtain these results taking into account the running of the Yukawa couplings of the fourth quark generation with the aid of the Renormalization Group (RG) equations, finding similar allowed values for the Higgs mass but a slightly lower cut-off due to the breaking of the perturbative regime. Such low cut-off means that the effects of new physics needed to describe electroweak interactions at energy above Λ should be measurable at the LHC. We use the minimal supersymmetric extension of the standard model with four generations as an explicit example of models realizing the dynamical electroweak symmetry breaking by radiative corrections and containing new physics. Here, the cutoff is replaced by the masses of the squarks and electroweak symmetry breaking by radiative corrections requires the squark masses to be of the order of 1 TeV.

hep-ph↗

arXiv2010

Z'-> ggg decay in left-right symmetric models with three and four fermion families

We study the Z'-> ggg decay in the context of a left-right symmetric gauge theory. We obtain a branching ratio BR(Z'-> ggg)=Γ(Z'->ggg)/ Γ(Z'-> q\bar{q})= (1.2-2.8) x 10^{-5} for m_{Z'}=(700-1500) GeV. We also study the contribution of a fourth fermion family. We find an enhancement in the branching ratio for Z' masses close to the \bar{b'}b' threshold and a dip for Z' masses close to the \bar{t'}t' threshold. Using the values of the fourth generation quark masses allowed by electroweak precision data we obtain a branching ratio BR(Z'-> ggg)= (1-6)x 10^{-5} for m_{Z'}=(700-1500) GeV.

hep-ph↗

arXiv2010

Charge asymmetries in e+e- -> pi+ pi- gamma at the phi resonance

We consider the forward-backward pion charge asymmetry for the e^{+}e^{-}\toπ^{+}π^{-}γprocess. At tree level we consider bremsstrahlung and double resonance contributions. Although the latter contribution is formally sub-leading, it is enhanced at low dipion invariant mass due to $ρ$ resonant effects. We consider also four alternative models to describe the final state radiation at the loop level: Resonance Chiral Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and Linear Sigma Model. The last three models yield results compatible with experimental data. The Kaon Loop Model requires an energy dependent phase to achieve the agreement.

hep-ph↗

arXiv2009

Deeply Bound Kaonic Clusters

In this talk I make a review on the theoretical and experimental situation around the deeply bound kaon clusters, the possible bound kaonic states of nuclear, rather than atomic nature. At the same time I discuss novel developments around other kind of bound kaon clusters, which include states of two mesons and one baryon, with either one or two kaons, and states of a vector meson and two kaons, which explain naturally the observed properties of the X(2175) and Y(4260) resonances.

nucl-th↗

arXiv2009

Is there an isovector companion of the X(2175)?

In this letter we study the reaction e^{+}e^{-}\toϕπ^0 ηwith the π^{0}ηsystem in an isoscalar s-wave configuration. We use a formalism recently developed for the study of e^{+}e^{-}\toϕππand e^{+}e^{-}\toϕK^{+}K^{-}. The obtained cross section is within the reach of present e^{+}e^{-} machines. Measuring this channel would test the absence of an isovector companion of the X(2175) as predicted by the three body approach to this resonance.

hep-ph↗

arXiv2009

Compton scattering off elementary spin 3/2 particles

We calculate Compton scattering off an elementary spin 3/2 particle in a recently proposed framework for the description of elementary high spin fields based on the projection onto eigen-subspaces of the Casimir operators of the Poincare group. We also calculate this process in the conventional Rarita-Schwinger formalism. Both formalisms yield the correct Thomson limit but the predictions for the angular distribution and total cross section differ beyond this point. We point out that the average squared amplitudes in the forward direction for Compton scattering off targets with spin s = 0, 1/2, 1 are energy-independent and have the common value 4e^4. As a consequence, in the rest frame of the particle the differential cross section for Compton scattering in the forward direction is energy independent and coincides with the classical squared radius. We show that these properties are also satisfied by a spin 3/2 target in the Poincare projector formalism but not by the Rarita-Schwinger spin 3/2 particle.

hep-th↗

arXiv2009

ϕK^{+}K^{-} production in electron-positron annihilation

In this work we study the e^{+}e^{-}\toϕK^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the γ*ϕ K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies using RχPT supplemented with the anomalous term for the VV'P interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in UχPT in the former case and the ones extracted from recent data on e^{+}e^{-}\to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(X\to ϕf_{0})Γ(X\to e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}\to ϕ K^{+}K^{-} around 2.2 GeV.

hep-ph↗

arXiv2008

X(2175) as a resonant state of the $ϕK \bar{K}$ system

We perform a Faddeev calculation for the three mesons system, $ϕK \bar{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K \bar{K}$ system around 970 MeV, very close to the $f_0(980)$ mass. The state appears in I=0 and qualifies as a $ϕf_0(980)$ resonance. We enlarge the space of states including $ϕππ$, since $ππ$ and $K \bar{K}$ build up the $f_0$ (980), and find moderate changes that serve to quantify theoretical uncertainties. No state is seen in I=1. This finding provides a natural explanation for the recent state found at BABAR and BES, the X(2175), which decays into $ϕf_0(980)$.

nucl-th↗

arXiv2008

Photo- and Electron-Production of Mesons on Nucleons and Nuclei

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $ηπ^0 p$ and $K^0 π^0 Σ^+$, together with related reactions will be shown, having with common denominator the excitation of the $Δ(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to ϕf_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $ω$ in nuclei, showing that present experimental results claiming a shift of the $ω$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $ω$ width in the nuclear medium.

nucl-th↗

arXiv2007

Electromagnetic couplings of elementary vector particles

On the basis of the three fundamental principles of (i) Poincaré symmetry of space time, (ii) electromagnetic gauge symmetry, and (iii) unitarity, we construct an universal Lagrangian for the electromagnetic interactions of elementary vector particles, i.e., massive spin-1 particles transforming in the /1/2,1/2) representation space of the Homogeneous Lorentz Group (HLG). We make the point that the first two symmetries alone do not fix the electromagnetic couplings uniquely but solely prescribe a general Lagrangian depending on two free parameters, here denoted by ξand g. The first one defines the electric-dipole and the magnetic-quadrupole moments of the vector particle, while the second determines its magnetic-dipole and electric-quadrupole moments. In order to fix the parameters one needs an additional physical input suited for the implementation of the third principle. As such, one chooses Compton scattering off a vector target and requires the cross section to respect the unitarity bounds in the high energy limit. In result, we obtain the universal g=2, and ξ=0 values which completely characterize the electromagnetic couplings of the considered elementary vector field at tree level. The nature of this vector particle, Abelian versus non-Abelian, does not affect this structure. Merely, a partition of the g=2 value into non-Abelian, g_{na}, and Abelian, g_{a}=2-g_{na}, contributions occurs for non-Abelian fields with the size of g_{na} being determined by the specific non-Abelian group appearing in the theory of interest, be it the Standard Model or any other theory.

hep-ph↗

arXiv2007

Electron-positron annihilation into phi f_{0}(980) and clues for a new 1^{--} resonance

We study the e^{+}e^{-} to phi pi pi reaction for pions in an isoscalar s-wave which is dominated by loop mechanisms. For kaon loops we start from the conventional RCHPT, but use the unitarized amplitude for KbarK-pipi scattering and the full kaon form factor instead of the lowest order terms. We study also effects of vector mesons using RCHPT supplemented with the conventional anomalous term for VVP interactions and taking into account the effects of heavy vector mesons in the K*K transition form factor. We find a peak in the dipion invariant mass around the f_{0}(980) as in the experiment. Selecting the phi f_{0}(980) contribution as a function of the e^{+}e^{-} energy we also reproduce the experimental data except for a narrow peak, yielding support to the existence of a 1^{--} resonance above the phi f_{0}(980) threshold, coupling strongly to this state.

hep-ph↗

arXiv2004

Equations of motion as projectors and the gyromagnetic factor g_{s}=1/s} from first principles

In this work we adopt the point of view that the equations of motion satisfied by a field are just a consequence of the representation space which the field belongs to, and the discrete symmetries we impose on it. We illustrate this view point by rederiving Dirac and Proca equations as projectors over the subspaces with well defined parity of (1/2,0)+(0,1/2) and (1/2,0)X(0,1/2) representations respectively. We formulate the equation of motion corresponding to the identification of elementary systems with states in the invariant subspaces of the squared Pauli-Lubanski operator and couple minimally to electromagnetism the corresponding equation for the (s,0)+(0,s) representation space using the gauge principle. We obtain g=1/s for particles with arbitrary spin s as conjectured by Belinfante long ago.

hep-ph↗

arXiv2003

Scalar f0(980) and sigma(500) meson exchange in phi decays into pi0pi0gamma

The complementarity between Chiral Perturbation Theory and the Linear Sigma Model is exploited to study $π^0π^0$ production in $ϕ$ radiative decays, where the effects of the $f_0(980)$ scalar resonance, and those of its more controversial $σ(500)$ partner, should become manifest via the $ϕ\to K^+ K^- (γ)\toπ^0π^0γ$ decay chain. The recently reported data on $ϕ\toπ^0π^0γ$ coming from the VEPP-2M $e^+ e^-$ collider in Novosibirsk and the DA$Φ$NE $ϕ$-factory in Frascati can be reasonably described in our approach, which we propose as a promising first step towards more detailed analyses. The $f_0(980)$ contribution, which appears as a moderately narrow peak at the high part of the dipion mass spectrum, can be interpreted as the isoscalar member of the scalar nonet with a large $f_0 K\bar{K}$ coupling and an $f_0ππ$ coupling suppressed by almost ideal $σ$-$f_0$ mixing. Indeed, the mixing angle in the flavour basis is found to be $ϕ_{S}\approx -6^\circ$, if the $f_0$-propagator is approximated by a simple Breit-Wigner, or $ϕ_{S}\approx -9^\circ$, if an improved two-channel analysis is performed. The $σ(500)$ resonance, which is then strongly coupled to pion pairs, yields a tiny contribution because, in our approach, its coupling to kaon pairs is proportional to $m^2_σ-m^2_K$ and thus quite small.

hep-ph↗

arXiv2002

Radiative decays of light vector mesons in a quark level linear sigma model

We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma decays in the framework of a U(3)xU(3) linear sigma model which includes constituent quarks. For the first two decays this approach improves results based on the anomalous Wess-Zumino term, with contributions due to SU(3) symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays are dominated by resonant eta' exchange . Our calculation for the later decays improves and update similar calculations in the -closely related- framework of vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the high-luminosity phi factories.

hep-ph↗

arXiv2001

Scalar sigma meson effects in rho and omega decays into pi0 pi0 gamma

The complementarity between Chiral Perturbation Theory and the Linear Sigma Model in the scalar channel is exploited to study $π^0π^0$ production in $ρ$ and $ω$ radiative decays, where the effects of a low mass scalar resonance $σ(500)$ should manifest. The recently reported data on $ρ\toπ^0π^0γ$ seem to require the contribution of a low mass and moderately narrow $σ(500)$. The properties of this controversial state could be fixed by improving the accuracy of these measurements. Data on $ω\toπ^0π^0γ$ can also be accommodated in our framework, but are much less sensitive to the $σ(500)$ properties.

hep-ph↗