arXiv subjects

E. S. Tututi

Publications and source records attributed to E. S. Tututi.

32 records · Page 2Linked to original sources

arXiv2014

Gauge invariant electromagnetic properties of fermions induced by CPT violation in the Standard Model Extension

Low-energy Lorentz-invariant quantities could receive contributions from a fundamental theory producing small Lorentz-violating effects. Within the Lorentz-violating extension of quantum electrodynamics, we investigate, perturbatively, the contributions to the one-loop $ffγ$ vertex from the $CPT$-violating axial coupling of a vector background field to fermions. We find that the resulting vertex function has a larger set of Lorentz structures than the one characterizing the usual, Lorentz invariant, parametrization of the $ffγ$ vertex. We prove gauge invariance of the resulting one-loop expression through a set of gauge invariant nonrenormalizable operators introducing new-physics effects at the first and second orders in Lorentz violation, and which generate tree-level contributions to the $ffγ$ vertex. Whereas loop contributions involving parameters that violate Lorentz invariance at the first order are $CPT$-odd, those arising at the second order are $CPT$-even, so that contributions to low-energy physics are restricted to emerge for the first time at the second order. In this context, we derive a contribution to anomalous magnetic moment of fermions, which we use to set a bound on Lorentz violation.

hep-ph↗

arXiv2013

Trilinear gauge boson couplings in the standard model with one universal extra dimension

One-loop effects of Standard Model (SM) extensions comprising universal extra dimensions are essential as a consequence of Kaluza-Klein (KK) parity conservation, for they represent the very first presumable virtual effects on low-energy observables. In this paper, we calculate the one-loop CP-even contributions to the SM WWgamma and WWZ gauge couplings produced by the KK excited modes that stand for the dynamical variables of the effective theory emerged from a generalization of the SM to five dimensions, in which the extra dimension is assumed to be universal, after compactification. The employment of a covariant gauge-fixing procedure that removes gauge invariance associated to gauge KK excited modes, while keeping electroweak gauge symmetry manifest, is a main feature of this calculation, which is performed in the Feynman 't Hooft gauge and yields finite results that consistently decouple for a large compactification scale. After numerical evaluation, our results show to be comparable with the one-loop SM contributions and well within the reach of a next linear collider.

hep-ph↗

arXiv2013

Lorentz-violating effects on pair production of W bosons in photon collisions

We examine Lorentz-violating effects that could appear through deviations of the Standard Model gauge couplings WWgamma and WWgammagamma. These new physics effects are explored on the gamma gamma -> WW reaction at the International Linear Collider. In particular, the associated helicity amplitudes are computed in the context of the Standard Model Extension (which is a model-independent approach to CPT and Lorentz violation) and the Effective Lagrangian Model (which incorporates new physics effects that respect CPT and Lorentz violation). We perform an exhaustive study of the polarized differential cross sections to stand out effects related to Lorentz symmetry violation, where it is evidenced that the effects of Lorentz symmetry violation are more sensitive to the presence of the b constant background field. We found that for the $(\pm,\pm,(L,T+T,L))$ polarization state, only Standard Model Extension and Effective Lagrangian Model contribute at the lowest order, however, both types of new physics effects are clearly distinguished, being dominant the convoluted cross section of the Standard Model Extension in around 4 orders of magnitude. For this polarization state, at the last stage of operation of International Linear Collider, it is expected an integrated luminosity of 10^3 fb^{-1}, finding around of 2 events for a Lorentz-violating energy scale of 32 TeV.

hep-ph↗

arXiv2013

Effects of Lorentz violation through the $γe\to Wν_e$ process in the Standard Model Extension

Physics beyond the Fermi scale could show up through deviations of the gauge couplings predicted by the electroweak Yang-Mills sector. This possibility is explored in the context of the International Linear Collider (ILC) through the helicity amplitudes for the gamma e -> W nu_e reaction to which contributes the trilinear WWgamma coupling. The new physics effects on this vertex are parametrized in a model-independent fashion through an effective electroweak Yang-Mills sector, which is constructed by considering two essentially different sources of new physics. In one scenario, Lorentz violation will be considered exclusively as the source of new physics effects. This type of new physics is considered in an extension of the Standard Model that is known as the Standard Model Extension (SME), which is an effective field theory that contemplates CPT and Lorentz violation in a model-independent fashion. Any source of new physics that respects the Lorentz symmetry, will be considered within the general context of the well known Conventional Effective Standard Model (CESM) extension. Both the SME and the CESM descriptions include gauge invariant operators of dimension higher than four, which, in general, transform as Lorentz tensors of rank higher than zero. Whereas in the former theory observer Lorentz invariants are constructed by contracting these operators with constant Lorentz tensors, in the latter the corresponding Lorentz invariant interactions are obtained contracting such operators with products of the metric tensor. We focus our study on the possibility of experimentally distinguish both types of new physics effects on the WWgamma vertex. It is found that for a new physics scale of the same order of magnitude and under determined circumstances, both types of new physics effects will be clearly distinguished.

hep-ph↗

arXiv2012

Study of the lepton flavor-violating $Z'\toτμ$ decay

The lepton flavor violating $Z^{\prime}\toτμ$ decay is studied in the context of several extended models that predict the existence of the new gauge boson named $Z^\prime$. A calculation of the strength of the lepton flavor violating $Z^\primeμτ$ coupling is presented by using the most general renormalizable Lagrangian that includes lepton flavor violation. We used the experimental value of the muon magnetic dipole moment to bound this coupling, from which the $\mathrm{Re}(Ω_{Lμτ}Ω^\ast_{Rμτ})$ parameter is constrained and it is found that $\mathrm{Re}(Ω_{Lμτ}Ω^\ast_{Rμτ})\sim 10^{-2}$ for a $Z^\prime$ boson mass of 2 TeV. Alongside, we employed the experimental restrictions over the $τ\toμγ$ and $τ\toμμ^+μ^-$ processes in the context of several models that predict the existence of the $Z^\prime$ gauge boson to bound the mentioned coupling. The most restrictive bounds come from the calculation of the three-body decay. For this case, it was found that the most restrictive result is provided by a vector-like coupling, denoted as $|Ω_{μτ}|^2$, for the $Z_χ$ case, finding around $10^{-2}$ for a $Z^\prime$ boson mass of 2 TeV. We used this information to estimate the branching ratio for the $Z^\prime\toτμ$ decay. According to the analyzed models the least optimistic result is provided by the Sequential $Z$ model, which is of the order of $10^{-2}$ for a $Z^\prime$ boson mass around 2 TeV.

hep-ph↗

arXiv2011

Z'tc coupling from D0-D0 mixing

We bound the $Z^\prime tc$ coupling using the $D^{0}-\bar{D^{0}}$ meson mixing system. We obtained such coupling which is less than $5.75\times 10^{-2}$. We have studied the $Z^\prime$ boson resonance considering single top production in the $e^+e^-\to Z^\prime\to tc$ process. We obtained the number of events which is expected to be less than $10^7$ at the International Linear Collider scenario. We get a branching ratio of the order of $10^{-2}$ for the $Z^\prime\to tc$ decay.

hep-ph↗

arXiv2011

Bounding the $Z^\prime tc$ coupling from $D^{0}-\bar{D^{0}}$ mixing and single top production at the ILC

In the present work the $Z^\prime tc$ coupling is bounded by using the current experimental data on the $D^{0}-\bar{D^{0}}$ meson-mixing system. It is found that the strength associated to this coupling is less than $5.75\times 10^{-2}$. The single top production through the $e^+e^-\to Z^\prime\to tc$ process at the $Z^\prime$ boson resonance is studied and we found that around $10^7$ $tc$ events will be expected at the International Linear Collider. For the $Z^\prime\to tc$ decay, we predict a branching ratio of $10^{-2}$.

hep-ph↗

arXiv2010

Higgs mediated flavor violating top quark decays t --> u_i H, u_i gamma, u_i gamma gamma, and the process gamma gamma --> t c in effective theories

The rare top quark couplings $tu_iγ$ and $tu_iγγ$ ($u_i=u,c$) induced at the one-loop level by a flavor violating $tu_iH$ vertex are studied within the context of an effective Yukawa sector that incorporates $SU_L(2)\times U_Y(1)$-invariant operators of up to dimension six. Data on the recently observed $D^0-\overline{D^0}$ mixing are employed to constrain the $tu_iH$ vertex, which is then used to predict the $t\to u_iH$, $t\to u_iγ$, and $t\to u_iγγ$ decays, as well as the $γγ\to \bar{t}u_i+t\bar{u}_i$ reaction in the context of the ILC. It is found that the $t\to cH$ and $t\to cγγ$ decays can reach sizable branching ratios as high as $5\times 10^{-3}$ and $10^{-4}$, respectively. As for the $t\to cγ$ decay, it can have a branching ratio of $5\times 10^{-8}$ that is about 6 orders of magnitude larger than the standard model prediction, which, however, is still very small to be detected. As for $tc$ production, it is found that, due to the presence of a resonant effect in the convoluted cross section $σ(e^+e^-\to γγ\to t\bar{c}+\bar{t}c)$, about $(0.5 - 2.7)\times 10^{3}$ $tc$ events may be produced at the ILC for a value of the Higgs mass near to the top mass.

hep-ph↗

arXiv2010

Bounding the B_s -> gamma gamma decay from Higgs mediated FCNC transitions

The Higgs mediated flavor violating bottom-strange quarks transitions induced at the one-loop level by a nondiagonal $Hbs$ coupling are studied within the context of an effective Yukawa sector that comprises $SU_L(2)\times U_Y(1)$-invariant operators of up to dimension-six. The most recent experimental result on $B\to X_sγ$ with hard photons is employed to constraint the $Hbs$ vertex, which is used to estimate the branching ratio for the $B_s\to γγ$ decay. It is found that the $B_s\to γγ$ decay can reach a branching ratio of the order of $4\times 10^{-8}$, which is 2 orders of magnitude more stringent than the current experimental limit.

hep-ph↗

arXiv2009

Implications of $D^0-\overline{D^0}$ on the rare top quark decays $t\to uγ$ and $t\to ug$

The recently observed mass difference of the $D^0-\overline{D^0}$ mixing is used to predict the branching ratios of the rare top quark decays $t\to uγ$ and $t\to ug$ in a model independent way using the effective Lagrangian approach. It is found that $Br(t\to uγ)<4\times 10^{-4}$ and $Br(t\to ug)<2\times 10^{-3}$, which still may be within reach of the LHC collider.

hep-ph↗

arXiv2009

Effective Lagrangian description of Higgs mediated flavor violating electromagnetic transitions: implications on lepton flavor violation

Higgs mediated flavor violating electromagnetic interactions, induced at the one--loop level by a nondiagonal $Hf_if_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $SU_L(2)\times U_Y(1)$--invariant operators of up to dimension--six. Exact formulae for the one--loop $γf_if_j$ and $γγf_if_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $μ\to eγ$ decay is used to derive a bound on the branching ratio of the $μ\to eγγ$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $τ\to μγ$ and $τ\to μγγ$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $γγ$ colliders is explored through the $γγ\to l_il_j$ reaction, putting special emphasis on the $τμ$ final state. Using the bound imposed on the $Hτμ$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.

hep-ph↗

arXiv2008

Higgs mediated lepton flavor violating tau decays $τ\to μγ$ and $τ\to μγγ$ in effective theories

The size of the branching ratios for the $τ\to μγ$ and $τ\to μγγ$ decays induced by a lepton flavor violating Higgs interaction $Hτμ$ is studied in the frame of effective field theories. The best constraint on the $Hτμ$ vertex, derived from the know measurement on the muon anomalous magnetic moment, is used to impose the upper bounds $Br(τ\to μγ)<2.5\times 10^{-10}$ and $Br(τ\to μγγ)<2.3\times 10^{-12}$, which are more stringent than current experimental limits on this class of transitions.

hep-ph↗

arXiv1998

Pressure of the Non-equilibrium O(N) Phi^{4} Theory in the Large N Limit

We calculate the off-equilibrium hydrostatic pressure for the O(N) Phi^{4} theory to the leading order in 1/N. The present paper, the first of a series, concentrates on the calculation of pressure in the non-equilibrium but translationally invariant medium. The Jaynes-Gibbs principle of maximal entropy is used to introduce the relevant density matrix which is then directly implemented into dynamical equations through generalised Kubo-Martin-Schwinger (KMS) conditions. We show that in the large N limit use of Ward identities enables the pressure to be expressed in terms of two point Green's functions. These satisfy the Kadanoff-Baym equations which are exactly solvable, and we explicitly calculate the pressure for three illustrative choices of ρ.

hep-th↗

arXiv1998

The Jaynes-Gibbs principle of maximal entropy and the non-equilibrium propagators of the O(N) phi^4 theory at large N

We present a novel procedure for calculating non-equilibrium two-point Green's functions in the $O(N) ϕ^{4}$ theory at large $N$. The non-equilibrium density matrix $ρ$ is constructed via the Jaynes-Gibbs principle of maximal entropy and it is directly implemented into the Dyson-Schwinger equations through initial value conditions. In the large $N$ limit we perform an explicit evaluation of two-point Green's functions for two illustrative choices of $ρ$.

hep-th↗