arXiv subjects

Bryan O. Larios

Publications and source records attributed to Bryan O. Larios.

7 recordsLinked to original sources

arXiv2020

Meronic AdS Black Holes in Gauss-Bonnet Theory

We examine analytical, intrinsically non-Abelian, black holes with SU(2) Yang-Mills matter content. Working in the extended thermodynamics scenario of Lovelock black holes we study the phase structure of a four and a five-dimensional spherically symmetric configuration. We work in Gauss-Bonnet-Einstein-Yang-Mills gravity with negative cosmological constant and use Euclidean methods to explore the thermodynamics of the systems. We observe that the solutions belong to the expected universality class of van der Waals and find a reentrant phase transition.

gr-qc↗

arXiv2019

Very long-lived Stop NLSP in MSSM scenarios with Gravitino LSP

We present the calculation of the stop ($\tilde{t}$) lifetime that results from its decay into gravitinos ($\tildeΨ^μ$) in the final state, namely $\tilde{t}\to \tildeΨ^μ + X$, where $X=t, bW, b lν_l$ for the two-, three- and four-body decay modes. The full calculation is obtained using the Feynman rules for massive gravitino, which is compared with the results obtained employing the equivalence theorem, where the longitudinal component of the gravitino is replaced by the goldstino. The stop turns out to be very long-lived in these scenarios, with lifetimes of $\mathcal{O}$($10^8$s, $10^{14}$s, $10^{20}$s) for the corresponding 2-,3- and 4-body modes under consideration, and therefore all of them are safe from the big bang nucleosynthesis problem. However, the lifetime for the four body decay mode occurs during the epoch of galaxy formation. When the stop is produce at colliders, in these scenarios, it will hadronize and decay outside of the detector, even for the lowest values of stop lifetime.

hep-ph↗

arXiv2017

Helicity Amplitudes for production of massive gravitino/goldstino

The spinor helicity formalism (SHF) has been efficiently applied to compute perturbative amplitudes in plenty of processes and reactions in gauge theories (including gravity), mostly in the massless case. Some work has been done in order to extend the SHF to the massive case. We have used these powerful tools to evaluate amplitudes in a local supersymmetric model where the gravitino is the lightest supersymmetric particle (LSP). Two decays have been evaluated in order to show the capability of the SHF in the massive extension, namely the two body neutralino decays $\tildeχ_0\to V\tildeΨ^μ$ with $V=γ, Z$. The comparisons of amplitudes with spin-3/2 gravitino and spin-1/2 goldstino are also presented.

hep-ph↗

arXiv2017

Helicity Amplitudes for massive gravitinos in N=1 Supergravity

We develop the formal tools needed to construct helicity amplitudes for massive gravitino in N=1 SUGRA. We start by considering the helicity states for massive spin-3/2 particles, which involves the solutions of Rarita-Schwinger equation. These solutions are written in terms of the helicity bra-ket notation and are used then to derive the interactions of gravitino with matter and gauge supermultiplets within N=1 Supergravity. The corresponding interactions of goldstinos are discussed too, relying on the goldstino-gravitino equivalence theorem. Finally to appreciate the power of our methods we evaluate the decay width chi_0 -> γG, as well as the cross sections for e^+ e- -> GG.

hep-ph↗

arXiv2016

An Introduction to the Massive Helicity Formalism with applications to the Electroweak SM

The power of the helicity formalism has been appreciated recently from its application to the massless case, where plenty of formal aspects of multi-legs amplitudes have been derived. However, in order to extend the formalism to the realistic cases, such as the electroweak Standard Model and QCD with massive quarks, some extra inputs are needed. We discuss first the formalism needed to evaluate amplitudes expressed with the modern notation for massive fermions and vectors based on a thorough treatment of Proca vector fields. Then, we present some examples of elementary processes where it is shown how the formalism leads to tremendous simplifications, these include 2-body decays $Z\to ff$, $h\to ff$ and $h\to W^{-}W^{+}$ as well as the 3-body decay $h\to V f'\bar{f}$.

hep-ph↗

arXiv2016

Stop Decay with LSP Gravitino in the final state: $\tilde{t}_1\to\widetilde{G}\,W\,b$

In MSSM scenarios where the gravitino is the lightest supersymmetric particle (LSP), and therefore a viable dark matter candidate, the stop $\tilde{t}_1$ could be the next-to-lightest superpartner (NLSP). For a mass spectrum satisfying: $m_{\widetilde{G}}+m_t>m_{\tilde{t}_1}>m_{\widetilde{G}}+m_b+m_W$, the stop decay is dominated by the 3-body mode $\tilde{t}_1\rightarrow b\,W\,\tilde{G}$. We calculate the stop life-time, including the full contributions from top, sbottom and chargino as intermediate states. We also evaluate the stop lifetime for the case when the gravitino can be approximated by the goldstino state. Our analytical results are conveniently expressed using an expansion in terms of the intermediate state mass, which helps to identify the massless limit. In the region of low gravitino mass ($m_{\widetilde{G}}\ll m_{\tilde{t}_1}$) the results obtained using the gravitino and goldstino cases turns out to be similar, as expected. However for higher gravitino masses $m_{\widetilde{G}} \lesssim m_{\tilde{t}_1}$ the results for the lifetime could show a difference of O(100)\%.

hep-ph↗

arXiv2012

On the Beaming of Gluonic Fields at Strong Coupling

We examine the conditions for beaming of the gluonic field sourced by a heavy quark in strongly-coupled conformal field theories, using the AdS/CFT correspondence. Previous works have found that, contrary to naive expectations, it is possible to set up collimated beams of gluonic radiation despite the strong coupling. We show that, on the gravity side of the correspondence, this follows directly (for arbitrary quark motion, and independently of any approximations) from the fact that the string dual to the quark remains unexpectedly close to the AdS boundary whenever the quark moves ultra-relativistically. We also work out the validity conditions for a related approximation scheme that proposed to explain the beaming effect though the formation of shock waves in the bulk fields emitted by the string. We find that these conditions are fulfilled in the case of ultra-relativistic uniform circular motion that motivated the proposal, but unfortunately do not hold for much more general quark trajectories.

hep-th↗