Mohammad T. AlFiky | Searcharxiv

arXiv2020

Viability of bouncing cosmology in energy-momentum-squared gravity

We analyze the early-time isotropic cosmology in the so-called energy-momentum-squared gravity (EMSG). In this theory, a $T_{μν}T^{μν}$ term is added to the Einstein-Hilbert action, which has been shown to replace the initial singularity by a regular bounce. We show that this is not the case, and the bouncing solution obtained does not describe our Universe since it belongs to a different solution branch. The solution branch that corresponds to our Universe, while nonsingular, is geodesically incomplete. We analyze the conditions for having viable regular-bouncing solutions in a general class of theories that modify gravity by adding higher order matter terms. Applying these conditions on generalizations of EMSG that add a $\left(T_{μν}T^{μν}\right)^{n}$ term to the action, we show that the case of $n=5/8$ is the only one that can give a viable bouncing solution, while the $n>5/8$ cases suffer from the same problem as EMSG, i.e. they give nonsingular, geodesically incomplete solutions. Furthermore, we show that the $1/2<n<5/8$ cases can provide a nonsingular initially de Sitter solution. Finally, the expanding, geodesically incomplete branch of EMSG or its generalizations can be combined with its contracting counterpart using junction conditions to provide a (weakly) singular bouncing solution. We outline the junction conditions needed for this extension and provide the extended solution explicitly for EMSG. In this sense, EMSG replaces the standard early-time singularity by a singular bounce instead of a regular one.

gr-qc↗

arXiv2006

Heavy Meson Molecules in Effective Field Theory

We consider the implications from the possibility that the recently observed state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We explore the consequences of the assumption that X(3872) is a molecular bound state of D^{*0} and anti-D^0 mesons for the existence of bound states in the D^0-anti-D^0 and D^{*0}-anti-D^{*0}.

hep-ph↗

arXiv2005

X(3872): Hadronic Molecules in Effective Field Theory

We consider the implications from the possibility that the recently observed state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We claim that if X(3872) is a molecular bound state of D^*0 and anti-D^0 mesons, the heavy-quark symmetry requires the existence of the molecular bound state X_b of B^*0 and anti-B^0 with the mass of 10604 MeV.

hep-ph↗