Spillway preheating

In traditional models only an order one fraction of energy is transferred from the inflaton to radiation through nonperturbative resonance production in preheating immediately after inflation, due to backreaction effects. We propose a particle production mechanism that could improve the depletion of the inflaton energy density by up to four orders of magnitude. The improvement comes from the fast perturbative decays of resonantly produced daughter particles. They act as a “spillway” to drain these daughter particles, reducing their backreaction on the inflaton and keeping the resonant production effective for a longer period. Thus we dub the scenario “spillway preheating”. We also show that the fraction of energy density remaining in the inflaton has a simple inverse power-law scaling in the scenario. In general, spillway preheating is a much more efficient energy dissipation mechanism, which may have other applications in model building for particle physics.

Probing the top-Higgs sector with composite Higgs models at present and future hadron colliders

We study the production of $$ t\overline{t}h $$ t t ¯ h and $$ t\overline{t} hh $$ t t ¯ hh at hadron colliders, in the minimal Composite Higgs Models, based on the coset SO(5)/SO(4). We explore the fermionic representations 5 and 14. A detailed phenomenological analysis is performed, covering the energy range of the LHC and its High Luminosity upgrade, as well as that of a future 100 TeV hadron collider. Both resonant and non-resonant production are considered, stressing the interplay and complementary interest of these channels with each other and double Higgs production. We provide sets of representative points with detailed experimental outcomes in terms of modification of the cross sections as well as resonance masses and branching ratios. For non-resonant production, we gauge the relative importance of Yukawa, Higgs trilinear, and contact $$ t\overline{t} hh $$ t t ¯ hh vertices to these processes, and consider the prospect for distinguishing the fermion representations from each other and from the Standard Model. In the production of top partners, we find that the three-body decay channel W+W–t becomes significant in certain regions of parameter space having a degenerate spectrum, and is further enhanced by increasing the top partner’s mass. This motivates both higher energy machines as well as the need to go beyond the current analysis performed for the searches for these resonances.

Probing top changing neutral Higgs couplings at colliders

The [Formula: see text] boson, discovered only in 2012, is lower than the top quark in mass, hence [Formula: see text] search commenced immediately thereafter, with current limits at the per mille level and improving. As the [Formula: see text] rate vanishes with the [Formula: see text]-[Formula: see text] mixing angle [Formula: see text], we briefly review the collider probes of the top changing [Formula: see text] coupling [Formula: see text] of the exotic [Formula: see text]-even/odd Higgs bosons [Formula: see text]. Together with an extra top conserving [Formula: see text] coupling [Formula: see text], one has an enhanced [Formula: see text] coupling alongside the familiar [Formula: see text] coupling, where [Formula: see text] is the charged Higgs boson. The main processes we advocate are [Formula: see text], [Formula: see text] (same-sign top and triple-top), and [Formula: see text]. We also discuss some related processes such as [Formula: see text], [Formula: see text] that depend on [Formula: see text] being nonzero, comment briefly on [Formula: see text] resonant production and touch upon the [Formula: see text] coupling.

Resonant Production of an Ultrarelativistic Electron–Positron Pair at the Gamma Quantum Scattering by a Field of the X-ray Pulsar

The process of a resonant production of an ultrarelativistic electron–positron pair in the process of gamma-quantum scattering in the X-ray field of a pulsar is theoretically studied. This process has two reaction channels. Under resonant conditions, an intermediate electron (for a channel A) or a positron (for a channel B) enters the mass shell. As a result, the initial second-order process of the fine-structure constant in the X-ray field effectively splits into two first-order processes: the X-ray field-stimulated Breit–Wheeler process and the the X-ray field-stimulated Compton effect on an intermediate electron or a positron. The resonant kinematics of the process is studied in detail. It is shown that for the initial gamma quantum there is a threshold energy, which for the X-ray photon energy (1–102) keV has the order of magnitude (103–10) MeV. In this case, all the final particles (electron, positron, and final gamma quantum) fly in a narrow cone along the direction of the initial gamma quantum momentum. It is important to note that the energies of the electron–positron pair and the final gamma quantum depend significantly on their outgoing angles. The obtained resonant probability significantly exceeds the non-resonant one. The obtained results can be used to explain the spectrum of positrons near pulsars.

Resonant production of electron-positron pairs by a hard gamma-ray on a nucleus in an external electromagnetic field

The resonant production of electron-positron pairs by a hard gamma-ray on nucleus in an external electromagnetic field is studied theoretically. The main property of this process is that the initial process of the second order in the fine structure constant in an external field effectively splits into two successive processes of the first order due to the fact that in resonant conditions intermediate virtual electron (positron) becomes a real particle. One of these processes is a single-photoproduction of electron-positron pair in a laser field (laser-stimulated Breit-Wheeler process) another is a laser-assisted scattering of electron (positron) on nucleus (laser-assisted Mott scattering). It is shown that the resonances are possible only for the energies of the initial hard gamma-ray more than the characteristic threshold energy. Resonant differential cross section of this process is obtained. It is shown that the resonant differential cross section can significantly exceed the corresponding cross section without an external field. The obtained results may be experimentally verified using the facilities of pulsed laser radiation (SLAC, FAIR, XFEL, ELI, XCELS).

Search for Excited u and d Quarks in Dijet Final States at Future pp Colliders

Resonant production of excited u and d quarks at the Future Circular Collider and Super Proton-Proton Collider has been researched. Dominant jet-jet decay mode has been considered. It is shown that FCC and SppC have great potential for discovery of excited u (d) quark: up to 44.1 (36.3) and 58.4 (47.8) TeV masses, respectively. For degenerate case (Mu⋆ = Md⋆), these values are 45.9 and 60.9 TeV, respectively. This discovery will also afford an opportunity to determine the compositeness scale up to multi-PeV level.