Generalised Ellis–Bronnikov wormholes embedded in warped braneworld background and energy conditions

Ellis–Bronnikov (EB) wormholes require violation of null energy conditions at the ‘throat’. This problem was cured by a simple modification of the ‘shape function’, which introduces a new parameter $$m\ge 2$$ m ≥ 2 ($$m=2$$ m = 2 corresponds to the EB model). This leads to a generalised (GEB) version. In this work, we consider a model where the GEB wormhole geometry is embedded in a five dimensional warped background. We studied the status of all the energy conditions in detail for both EB and GEB embedding. We present our results analytically (wherever possible) and graphically. Remarkably, the presence of decaying warp factor leads to satisfaction of weak energy conditions even for the EB geometry, while the status of all the other energy conditions are improved compared to the four dimensional scenario. Besides inventing a new way to avoid the presence of exotic matter, in order to form a wormhole passage, our work reveals yet another advantage of having a warped extra dimension.

A warped scalar portal to fermionic dark matter

We argue that extensions of the SM with a warped extra dimension, together with a new $${\mathbb {Z}}_2$$ Z 2 -odd scalar singlet, provide a natural explanation not only for the hierarchy problem but also for the nature of fermion bulk masses and the observed dark matter relic abundance. In particular, the Kaluza-Klein excitations of the new scalar particle, which is required to naturally obtain fermion bulk masses through Yukawa-like interactions, can be the leading portal to any fermion propagating into the bulk of the extra dimension and playing the role of dark matter. Moreover, such scalar excitations will necessarily mix with the Higgs boson, leading to modifications of the Higgs couplings and branching ratios, and allowing the Higgs to mediate the coannihilation of the fermionic dark matter. We study these effects and explore the viability of fermionic dark matter in the presence of these new heavy scalar mediators both in the usual freeze-out scenario and in the case where the freeze-out happens during an early period of matter domination.

Lightening gravity-mediated dark matter

We revisit the scenario of a massive spin-2 particle as the mediator for communicating between dark matter of arbitrary spin and the Standard Model. Taking the general couplings of the spin-2 particle in the effective theory, we discuss the thermal production mechanisms for dark matter with various channels and the dark matter self-scattering. For WIMP and light dark matter cases, we impose the relic density condition and various experimental constraints from direct and indirect detections, precision measurements as well as collider experiments. We show that it is important to include the annihilation of dark matter into a pair of spin-2 particles in both allowed and forbidden regimes, thus opening up the consistent parameter space for dark matter. The benchmark models of the spin-2 mediator are presented in the context of the warped extra dimension and compared to the simplified models.

Implications of diphoton searches for a radion in the bulk-Higgs scenario

In this work, we point out that the apparent diphoton excess initially presented by the ATLAS and CMS collaborations could have originated from a radion in the bulk Higgs scenario within a warped extra dimension. In this scenario, the couplings of the radion to massive gauge bosons are suppressed, allowing it to evade existing searches. In the presence of mixing with the Higgs, due to the strong constraints from diboson searches, only points near what we denominate the alignment region were able to explain the diphoton signal and evade other experimental constraints. In light of the new measurements presented at ICHEP 2016 by both LHC collaborations, which do not confirm the initial diphoton excess, we study the current and future collider constraints on a radion within the bulk-Higgs scenario. We find that searches in the diphoton channel provide the most powerful probe of this scenario and already exclude large regions of parameter space, particularly for smaller warp factors. The radion has a sizeable branching ratio into top pairs and this channel may also give competitive constraints in the future. Finally, di-Higgs searches can provide a complementary probe in the case of nonzero radion-Higgs mixing but strong alignment.