arXiv subjects

A. R. Vieira

Publications and source records attributed to A. R. Vieira.

24 records · Page 2Linked to original sources

arXiv2016

Momentum Routing Invariance in Extended QED: Assuring Gauge Invariance Beyond Tree Level

We address the study of gauge invariance in the Standard Model Extension which encompasses all Lorentz-violating terms originated by spontaneous symmetry breaking at the Planck scale. In particular, we fully evaluate Ward identities involving two and three point functions and derive the conditions which assure gauge invariance of the electromagnetic sector of the Standard Model Extension at one-loop. We show that momentum routing invariance is sufficient to fix arbitrary and regularization dependent parameters intrinsic to perturbation theory in the diagrams involved. A scheme which judiciously collects finite but undetermined quantum corrections is employed, a particularly subtle issue in the presence of $γ_5$ matrices.

hep-th↗

arXiv2015

One-loop conformal anomaly in an implicit momentum space regularization framework

In this paper we consider matter fields in a gravitational background in order to compute the breaking of the conformal current at one-loop order. Standard perturbative calculations of conformal symmetry breaking expressed by the non-zero trace of the energy-momentum tensor have shown that some violating terms are regularization dependent, which may suggest the existence of spurious breaking terms in the anomaly. Therefore, we perform the calculation in a momentum space regularization framework in which regularization dependent terms are judiciously parametrized. We compare our results with those obtained in the literature and conclude that there is an unavoidable arbitrariness in the anomalous term $\Box R$.

hep-th↗

arXiv2014

Guises and Disguises of Quadratic Divergences

In this contribution, we present a new perspective on the control of quadratic divergences in quantum field theory, in general, and in the Higgs naturalness problem, in particular. Our discussion is essentially based on an approach where UV divergences are parameterized, after being reduced to basic divergent integrals (BDI) in one internal momentum, as functions of a cutoff and a renormalization group scale $λ$. We illustrate our proposal with well-known examples, such as the gluon vacuum self energy of QCD and the Higgs decay in two photons within this approach. We also discuss frameworks in effective low-energy QCD models, where quadratic divergences are indeed fundamental.

hep-ph↗

arXiv2014

Arbitrariness in the gravitational Chern-Simons-like term induced radiatively

Lorentz violation through a radiatively induced Chern-Simons-like term in a fermionic theory embedded in linearized quantum gravity with a Lorentz- and CPT-violating axial-vector term in the fermionic sector proportional to a constant field $b_μ$ has been recently studied. In a similar fashion as for the extended-QED model of Carroll-Field-Jackiw, we explicitly show that neither gauge invariance nor the more stringent momentum routing invariance condition on underlying Feynman diagrams fix the arbitrariness inherent to such induced term at one loop order. We present the calculation in a nonperturbative expansion in $b_μ$ and within a framework which besides operating in the physical dimension (and thus avoiding $γ_5$ matrix Clifford algebra ambiguities), judiciously parametrizes regularization dependent arbitrary parameters usually fixed by symmetries.

hep-th↗

arXiv2013

Geometry in the entanglement dynamics of the double Jaynes-Cummings model

We report on the geometric character of the entanglement dynamics of to pairs of qubits evolving according to the double Jaynes-Cummings model. We show that the entanglement dynamics for the initial states |ψ_0> = Cosα |1 0> + Sinα |0 1> and |ϕ_0> = Cosα |1 1> + Sinα |0 0> cover 3-dimensional surfaces in the diagram C_ij\timesC_ik\timesC_il, where C_mn stands for the concurrence between the qubits m and n, varying 0\leqα\leqπ/2. In the first case projections of the surfaces on a diagram C_ij\timesC_kl are conics. In the second case the curves can be more complex. We relate those conics with a measurable quantity, the {\it predictability}.We also derive inequalities limiting the sum of the squares of the concurrence of every bipartition and show that sudden death of entanglement is intimately connected to the size of the radius of a hyper-sphere.

quant-ph↗

arXiv2013

Naturalness and theoretical constraints on the Higgs boson mass

Arbitrary regularization dependent parameters in Quantum Field Theory are usually fixed on symmetry or phenomenology grounds. We verify that the quadratically divergent behavior responsible for the lack of naturalness in the Standard Model (SM) is intrinsically arbitrary and regularization dependent. While quadratic divergences are welcome for instance in effective models of low energy QCD, they pose a problem in the SM treated as an effective theory in the Higgs sector. Being the very existence of quadratic divergences a matter of debate, a plausible scenario is to search for a symmetry requirement that could fix the arbitrary coefficient of the leading quadratic behavior to the Higgs boson mass to zero. We show that this is possible employing consistency of scale symmetry breaking by quantum corrections. Besides eliminating a fine-tuning problem and restoring validity of perturbation theory, this requirement allows to construct bounds for the Higgs boson mass in terms of $δm^2/m^2_H$ (where $m_H$ is the renormalized Higgs mass and $δm^2$ is the 1-loop Higgs mass correction). Whereas $δm^2/m^2_H<1$ (perturbative regime) in this scenario allows the Higgs boson mass around the current accepted value, the inclusion of the quadratic divergence demands $δm^2/m^2_H$ arbitrarily large to reach that experimental value.

hep-ph↗