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Antonio O. Bouzas

Publications and source records attributed to Antonio O. Bouzas.

At least 19 recordsLinked to original sources
arXiv2026

Cartesian isotropic tensors revisited

An alternative, streamlined methodology is presented for deriving the isotropic Cartesian tensor bases under the special orthogonal group $\text{SO}(3)$. By shifting the traditional interpretation of the isotropy condition to analyze it as an algebraic system of equations for the rotation matrices themselves rather than the tensor components, lower-rank bases can be explicitly established in just a few lines without requiring finite coordinate rotations or complicated contractions of infinitesimal generators. Furthermore, a transparent combinatorial interpretation is provided for the number of tensors in the general higher-rank spanning sets. Finally, the Gram-matrix method is advocated as an efficient computational sieve to resolve the subsequent linear dependence.

physics.class-ph↗
arXiv2025

The vector potential of a steady azimuthal current density. Once again

We give an integral expression for the vector potential of a time-independent, steady azimuthal current density. Our derivation is substantially simpler and somewhat more general than others given in the literature. As an illustration, we recover the results for the vector potential of a circular current loop as an orthogonal expansion in spherical and cylindrical coordinates. Additionally, we obtain closed analytical expressions for the vector potential and the magnetic induction of a circular current loop in terms of Legendre functions of the second kind, that are simpler than the results in terms of complete elliptic integrals given in textbooks.

physics.class-ph↗
arXiv2025

Probing $|V_{td}|$ in single-top production at $pe^{\mp}$ colliders

We study the consequences for top-quark physics of having electron and positron beams available at the LHeC and FCC-he, as was the case in HERA. We show that the asymmetry between top production in $pe^+$ collisions and antitop production in $pe^-$ reactions is sensitive to $|V_{td}|$. By means of detailed parton-level Monte Carlo simulations of single $t$ and $\bar{t}$ production and its backgrounds, we parametrize the asymmetry dependence on $|V_{td}|$ and estimate its uncertainties. Our analysis includes realistic phase-space cuts, and machine-learning binary classifiers for background rejection. We thus obtain limits on $|V_{td}|$ that are substantially stronger than current ones, and also smaller than current projections for the HL-LHC. We have $|V_{td}| < 1.6\times |V_{td}^\mathrm{PDG}|$ at the LHeC, at 68\% C.L.\ with $L_\mathrm{int}=2$/ab.

hep-ph↗
arXiv2024

Top quark flavor changing couplings at a muon collider

There is growing interest in the development of a muon collider that would make it possible to produce lepton collisions at energies of several TeV. Among others, there can be significant contributions to electroweak gauge boson, Higgs boson and top quark physics. In this work we pay attention to the latter, in particular, effective flavor-changing (FC) top-quark interactions. We discuss the flavor changing $t \bar q$ ($q=u,c$) production processes that can be a good probe of the dimension-six top quark four-fermion and fermion-boson operators in the SMEFT. We consider all sixteen operators that can generate flavor-changing top quark couplings. After comparing with the current LHC bounds, we find potential limits three or four orders of magnitude stronger for four-fermion operators. Concerning fermion-boson couplings, for the tensor operators $Q_{uW}$ and $Q_{uB}$ we obtain the highest sensitivity. We also observe that the effective $W$ approximation (EWA) does not apply with $Q_{uB}$.

hep-ph↗
arXiv2023

Top quark effective couplings from top-pair tagged photoproduction in $pe^-$ collisions

We present a detailed study, at the fast detector simulation level, of top-pair photoproduction in semileptonic mode at the LHeC and FCC-he future colliders. We work in full tree-level QED, not relying on the equivalent-photon approximation, taking into account the complete photoproduction kinematics. This allows us to define three photoproduction regions based on the angular acceptance range of the electron tagger. Those regions provide different degrees of sensitivity to top-quark effective couplings. We focus on the $t\bar{t}γ$ dipole couplings and the left-handed vector $tbW$ coupling for which we determine limits at both energies and in different photoproduction regions. We find that the LHeC and FCC-he will yield tight direct bounds on top dipole moments, greatly improving on current direct limits from hadron colliders, and direct limits on the $tbW$ coupling as restrictive as those expected from the HL-LHC. We also consider indirect limits from $b\to s γ$ branching ratio and $CP$ asymmetry, that are well known to be very sensitive probes of top electromagnetic dipole moments.

hep-ph↗
arXiv2023

Top quark effective couplings from top-pair tagged photoproduction in $\boldsymbol{pe^-}$ collisions

We summarize the quantitative results of our analysis [1] of top-pair photoproduction in semileptonic mode in $pe$ collisions at the LHeC and FCC-he. We define three photoproduction regions, based on the rapidity acceptance range of the electron tagger, that provide different degrees of sensitivity to top-quark effective couplings. We focus on the $t\bar{t}γ$ dipole couplings and the left-handed vector $tbW$ coupling, for which we determine limits at both energies in the different photoproduction regions. We find that the LHeC and FCC-he will yield tight direct bounds on top dipole moments, greatly improving on current direct limits from hadron colliders, and direct limits on the $tbW$ coupling as restrictive as those expected from the HL-LHC. We also consider indirect limits from $b\to s γ$ branching ratio and $CP$ asymmetry, that are well known to be very sensitive probes of top electromagnetic dipole moments.

hep-ph↗
arXiv2021

Two-to-two processes at an electron-muon collider

Based on a recent proposal to build an electron-muon collider, we study two-to-two production processes e^- mu^+ --> f bar-f, gamma gamma that originate from dimension 6 and 8 operators. We compare the sensitivity to those effective couplings obtained at the collider with that of low energy measurements of mu --> e gamma, mu --> e bar-e e and mu --> e conversion that have recently been reported in the literature. Whereas for the production of first family fermions the sensitivity of the collider processes is much weaker, for the second and third family fermions it is similar or stronger than that of low-energy processes. In the case of e^- mu^+ --> gamma gamma, the sensitivity to a dimension 8 contact operator turns out to be the strongest in comparison.

hep-ph↗
arXiv2017

Single top production at linear $e^-e^+$ colliders

We study single top production at linear lepton colliders with $\sqrt{s} = 0.5$, 1 and 3 TeV. A preliminary analysis shows that despite the large $t\bar t$ background at $\sqrt{s} = 0.5$ and 1 TeV it is possible to obtain a good sensitivity to the $tbW$ vertex; even more so at 3 TeV when single top becomes the dominant mode of production. Concerning the four dimension six operators involved, two of them simultaneously generate $ttZ$ couplings and their sensitivity decreases with energy. The opposite is true for the other two operators. Single top production at these machines is also useful to probe charged-current four fermion operators $eνbt$, some of which are related to $tbW$ operators through the equations of motion.

hep-ph↗
arXiv2016

The Wigner-Eckart Theorem for Reducible Symmetric Cartesian Tensor Operators

We explicitly establish a unitary correspondence between spherical irreducible tensor operators and cartesian tensor operators of any rank. That unitary relation is implemented by means of a basis of integer-spin wave functions that constitute simultaneously a basis of the spaces of cartesian and spherical irreducible tensors. As a consequence, we extend the Wigner--Eckart theorem to cartesian irreducible tensor operators of any rank, and to totally symmetric reducible ones. We also discuss the tensorial structure of several standard spherical irreducible tensors such as ordinary, bipolar and tensor spherical harmonics, spin-polarization operators and multipole operators. As an application, we obtain an explicit expression for the derivatives of any order of spherical harmonics in terms of tensor spherical harmonics.

quant-ph↗
arXiv2015

Limits on the anomalous $Wtq$ couplings

Within the model-independent framework of $SU(3)\times SU(2)\times U(1)$ gauge-invariant dimension-six operators, we study flavor-changing $Wtq$ couplings ($q=d,s$) and related four-quark contact interactions involving the top. We obtain bounds on those couplings from Tevatron and LHC data for single-top production and branching fractions in top decays, as well as other experimental results on flavor-changing neutral-current processes including $B\to X_{q}γ$ and $Z\to b\bar{q}$ decays ($q=d,s$). We also update the bounds on flavor-diagonal $Wtb$ couplings using the most recent measurement of $W$-helicity fractions in top decays from top-pair production.

hep-ph↗
arXiv2015

Analysis of the top-quark charged-current coupling at the LHeC

In the context of $SU(2)_L\times U(1)$ dimension six operators we study the potential of the LHeC to provide information on top quark effective interactions. We focus on single antitop production and how it is affected not only by the effective $tbW$ coupling but also by four-fermion operators. Compared to the LHC, the LHeC provides a cleaner environment to make a precise measurement of the top quark production cross section. Therefore, this machine would give a much better assesment of $V_{tb}$ in the context of the SM or $V_L$ in the context of higher dimension operators. The LHeC could also give a slightly better measurement for $V_R$. For $g_R$ the HL-LHC precise measurements of $F_L$ and $F_R$ (the $W$-boson helicity decay ratios of top) would yield better constraints than those obtained by the LHeC. Lepton-quark contact interactions would also be significantly better probed by the LHeC, since the only way of measuring them at the LHC would be through leptonic top decay which is hardly sensitive to these interactions.

hep-ph↗
arXiv2013

Probing $ttγ$ and $ttZ$ couplings at the LHeC

We study the deep inelastic scattering and photo-production modes of $t\overline{t}$ pairs at the proposed LHeC and its potential to probe the electromagnetic and weak dipole moments (MDM and EDM for $ttγ$) of the top quark. A framework of eight independent gauge-invariant dimension-six operators involving the top quark and the electroweak gauge bosons is used. Four of these operators modify the charged $tbW$ coupling which can be probed through the single (anti) top production mode as reported in the literature. One generates $ttγ(Z)$ as well as $tbW$ couplings, while the other two do not generate $tbW$ but only $ttγ(Z)$. Our focus is on the MDM and EDM of the top quark for which the photo-production mode of $t\overline{t}$ can be an excellent probe. At the proposed electron energies of $E_e =60$ and $140$ GeV the LHeC could set constraints stronger than the indirect limits from $b\to s γ$ and the potential limits of the LHC through $t\overline{t} γ$ production.

hep-ph↗
arXiv2013

Electromagnetic dipole moments of the top quark

Recent measurements like the t tbar gamma production by CDF as well as the Br(B ->Xs gamma) and ACP (B->Xs gamma) are used to constrain the magnetic and electric dipole moments of the top quark. The B->Xs gamma measurements by themselves define an allowed parameter region that sets up stringent constraints on both dipole moments. Actually, significantly more stringent than previously reported. The measurement by CDF has a 37% error that is too large to set any competitive bounds, for which a much lower 5% error would be required at least. On the other hand, because of the LHC's higher energy (apart from its higher luminosity) the same measurement performed there could indeed further constrain the allowed parameter region given by the B->Xs gamma measurement.

hep-ph↗
arXiv2011

Addition theorems for spin spherical harmonics. I Preliminaries

We develop a systematic approach to deriving addition theorems for, and some other bilocal sums of, spin spherical harmonics. In this first part we establish some necessary technical results. We discuss the factorization of orbital and spin degrees of freedom in certain products of Clebsch-Gordan coefficients, and obtain general explicit results for the matrix elements in configuration space of tensor products of arbitrary rank of the position and angular-momentum operators. These results are the basis of the addition theorems for spin spherical harmonics obtained in part II.

math-ph↗
arXiv2011

Steady states of the parametric rotator and pendulum

We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the damped, non-linear equation of motion of the parametric rotator and pendulum perturbatively for small parametric excitation and damping, although our perturbative approach can be extended to other regimes as well. Our treatment involves only ordinary second-order differential equations with constant coefficients, and provides numerically accurate perturbative solutions in terms of elementary functions. Some of the steady-state rotation and oscillation modes studied here have not been discussed in the previous literature. Other well-known ones, such as parametric resonance and the inverted pendulum, are extended to elliptic parametric excitation tilted with respect to gravity. The results presented here should be accessible to advanced undergraduates, and of interest to graduate students and specialists in the field of non-linear mechanics.

physics.class-ph↗
arXiv2011

QCD correction to single top quark production at the ILC

Single top quark production at the ILC can be used to obtain a high precision measurements of the the Vtb CKM matrix element as well as the effective tbW coupling. We have calculated the QCD correction for the cross section in the context of an effective vector boson approximation. Our results show a 10% increase due to the strong interaction.

hep-ph↗
arXiv2010

Polarized $pK^-$ scattering in Unitary Baryon Chiral Perturbation Theory

We study $pK^-$ scattering in the energy range from threshold through the $Λ(1520)$ peak in UBChPT, taking into account $\mathcal{O}(q)$ vertices from meson-baryon contact interactions and $s$- and $u$-channel ground-state baryon exchange, $s$- and $u$-channel decuplet- and nonet-baryon exchange and $t$-channel vector-meson exchange, as well as $\mathcal{O}(q^2)$ flavor-breaking vertices. Detailed fits to data are presented, including a substantial body of differential cross-section data with meson momentum $q_\mathrm{lab} > 300$ MeV not considered in previous treatments.

hep-ph↗