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G. Valencia

Publications and source records attributed to G. Valencia.

At least 55 records · Page 3Linked to original sources
arXiv1999

Additional Isospin-Breaking Effects in ε^\prime/ε

In the analysis of ε^\prime/εit has been traditional to consider the isospin-breaking effects arising from electroweak-penguin contributions and from π^0-ηand π^0-η^\prime mixing, yet additional isospin-violating effects exist. In particular, we study the isospin violation which arises from the u-d quark mass difference in the hadronization of the gluonic penguin operator, engendering contributions of an effective ΔI=3/2 character. Using chiral perturbation theory and the factorization approximation for the hadronic matrix elements, we find within a specific model for the low-energy constants that we can readily accommodate an increase in ε^\prime/εby a factor of two.

hep-ph↗
arXiv1998

CP Violation in Non-Leptonic Omega^- Decays

We estimate the size of the CP-violating rate asymmetry for the decay Omega^- -> Cascade + pion. Within the standard model we find a value of 2 x 10^(-5), and it could be as much as ten times larger if new physics is responsible for CP violation. Even though our calculation suffers from the usual uncertainty in the estimate of hadronic matrix elements, we find a rate asymmetry that is significantly larger than the corresponding one for octet-hyperon decays.

hep-ph↗
arXiv1998

|Delta I|=3/2 Decays of the Omega^- in Chiral Perturbation Theory

We study the decays Omega^- -> Cascade+pion using heavy-baryon chiral perturbation theory to quantify the |Delta I|=1/2 rule in these decay modes. The ratio of |Delta I|=3/2 to |Delta I|=1/2 amplitudes is somewhat larger in these decays than it is in other hyperon decays. At leading order there are two operators responsible for the |Delta I|=3/2 parts of the Omega^- decays which also contribute at one loop to other hyperon decays. These one-loop contributions are sufficiently large to indicate (albeit not definitely) that the measured width ratio of Omega^-->Cascade^0+pion^- to Omega^-->Cascade^-+pion^0 = 2.7 may be too large.

hep-ph↗
arXiv1998

Long Distance Contribution to $K_L \to \ell^+ \ell^-$

We revisit the calculation of the long distance contribution to $K_L \to μ^+ μ^-$. We discuss this process within the framework of chiral perturbation theory, and also using simple models for the $K_L γ^* γ^*$ vertex. We argue that it is unlikely that this mode can be used to extract information on short distance parameters. The process $K_L \to e^+ e^-$ is also long-distance dominated and we find that $B(K_L \to e^+ e^-) \approx 9 \times 10^{-12}$.

hep-ph↗
arXiv1997

CP Violating Anomalous Couplings at a 500 GeV e+ e- Linear Collider

We study the sensitivity of a 500 GeV $e^+e^-$ Linear Collider to $CP$ violating anomalous couplings. We find that with 50~fb$^{-1}$, and taking only one non-zero coupling at a time, the process $e^+e^-\to W^+ W^-$ can be used to place the 95% confidence level bounds $|\tildeκ_γ|\leq0.1$, $|\tildeκ_Z|\leq 0.1$ and $|g_4^Z|\leq 0.1$ from CP even observables. By studying certain distributions in the process $e^+e^-\to μ^+μ^-ν\barν$ one of the bounds can be improved to $|g_4^Z| \leq 0.06$. This process also allows the construction of a CP odd observable which can be used to place bounds on CP violating new physics. At the 95% confidence level we find $|\tildeκ_γ|\leq 0.3$, $|\tildeκ_Z|\leq 0.2$ and a much weaker bound for $|g_4^Z|$.

hep-ph↗
arXiv1997

CP Violation in B Decays from Anomalous tbW Interactions

We calculate the effect of new CP violating interactions parameterized by an anomalous $tbW$ coupling on CP-odd observables in B decays. We find that couplings consistent with current bounds induce observable effects in some CP asymmetries that will be measured in B-factories. The new effects are sufficiently large that they can actually test specific models that give rise to these $tbW$ interactions.

hep-ph↗
arXiv1997

Delta I=3/2 and Delta S =2 Hyperon Decays in Chiral Perturbation Theory

We study the Delta I =3/2 and Delta S =2 amplitudes for hyperon decays of the form (B to B(prime) pion) at lowest order in chiral perturbation theory. At this order, the Delta I=3/2 amplitudes depend on only one constant. We extract the value of this constant from experiment and find a reasonable description of these processes within experimental errors. The same constant determines the Delta S =2 transitions which, in the standard model, are too small to be observed. We find that new physics with parity odd Delta S=2 interactions can produce observable rates in hyperon decays while evading the bounds from K0 - K0(bar) mixing.

hep-ph↗
arXiv1996

The decays $K \to ππν\overlineν$ within the standard model

We study the reactions $K \rightarrow ππν\overlineν$ within the minimal standard model. We use isospin symmetry to relate the matrix elements to the form factors measured in $K_{\ell 4}$. We argue that these modes are short distance dominated and can be used for precise determinations of the CKM parameters $ρ$ and $η$. Depending on the value of the CKM angles we find branching ratios in the following ranges: $B(K_L \rightarrow π^+ π^- ν\overlineν) = [2-5] \times 10^{-13}$; $B(K_L \rightarrow π^0 π^0 ν\overlineν) = [1-3] \times 10^{-13}$; $B(K^+ \rightarrow π^+ π^0 ν\overlineν) = [1-2] \times 10^{-14}$. We also discuss a possible $CP$-odd observable.

hep-ph↗
arXiv1996

Probing Quartic Couplings Through Three Gauge Boson Production at an $e^+e^-$ Linear Collider

We explore the capability of a 500 or 1000 GeV $e^+e^-$ linear collider to measure anomalous quartic gauge boson couplings. In the framework of a non-linear effective Lagrangian with a custodial $SU)2)$ symmetry, there are only two next-to-leading order operators which contribute to quartic, but not to two- and three- gauge boson interactions. The limits on the coefficients of these operators from present and future $e^+e^-$ colliders are compared with those available from other sources.

hep-ph↗
arXiv1996

CP Violation in $Wγ$ and $Zγ$ Production

We study the capability of a $2 TeV$ $p\overline{p}$ collider with an integrated luminosity of $10 fb^{-1}$ to study CP violation in the processes $p \bar{p} \ra W^\pm γ$ and $p \bar{p} \ra Z γ$. We assume the existence of new CP violating interactions beyond the standard model which we describe with an effective Lagrangian. We find that the study of CP-odd observables would allow this machine to place bounds on CP violating anomalous couplings similar to the bounds that the same machine can place on $\cp$ conserving anomalous couplings. For example it could place the bound $|\tildeκ_γ|<0.1$ at the 95% confidence level.

hep-ph↗
arXiv1995

Study of Anomalous Couplings at a $500$~GeV $e^+e^-$ Linear Collider with Polarized Beams

We consider the possibility of observing deviations from the Standard Model gauge-boson self-couplings at a future $500$~GeV $e^+ e^-$ linear collider. We concentrate on the case in which the electroweak symmetry breaking sector is strongly interacting and there are no new resonances within reach of the collider. We find a sensitivity to the anomalous couplings that is two orders of magnitude higher than that achievable at LEP II. We also show how a polarized electron beam extends the reach of the collider, allowing experiments to probe different directions in parameter space.

hep-ph↗
arXiv1995

Theoretical Aspects of CP Violation in Hyperon Decays

I review the estimate of the CP violating asymmetry $A(Λ^0_-)$ within the standard model. I then review the estimate of the upper bound on this asymmetry that arises from measurements of CP violation in kaon decays.

hep-ph↗
arXiv1995

Limits on Non-Standard Top Quark Couplings from Electroweak Measurements

We calculate the typical size of loop corrections to electroweak observables arising from non-standard $Z {\overline t } t$ and $W t b$ vertices. We use an effective Lagrangian formalism based on the electroweak gauge group $SU(2)_L\times U(1)_Y \rightarrow U(1)_{EM}$. Limits on the non-standard model top quark couplings from electroweak observables are presented and compared with previously obtained limits.

hep-ph↗
arXiv1995

CP Violation in $Lambda \to p π^-$ Beyond the Standard Model

The $\cp$ violating asymmetry $A(Λ^0_-)$ has been estimated to occur at the level of a few times $10^{-5}$ within the minimal standard model. The experiment E871 expects to reach a sensitivity of $10^{-4}$ to the asymmetry $A(Λ^0_-)+A(Ξ^-_-)$. In this paper we study some of the implications of such a measurement for $\cp$ violation beyond the minimal standard model. We find that it is possible to have $A(Λ^0_-)$ at the few times $10^{-4}$ level while satisfying the constraints imposed by the measurements of $\cp$ violation in kaon decays.

hep-ph↗
arXiv1995

Looking for CP Violation in W Production and Decay

We describe CP violating observables in resonant $W^\pm$ and $W^\pm$ plus one jet production at the Tevatron. We present simple examples of CP violating effective operators, consistent with the symmetries of the Standard Model, which would give rise to these observables. We find that CP violating effects coming from new physics at the $TeV$ scale could in principle be observable at the Tevatron with $10^6$ $W^\pm$ decays.

hep-ph↗
arXiv1994

CP Violation in Hyperon Decays

In this talk we review the status of the theoretical estimates for CP violating asymmetries in non-leptonic hyperon decays.

hep-ph↗