We argue for the existence of bounds on the tensions of $\textit{p}$-branes in de Sitter space in terms of the Hubble rate and the strength of a class of Chern-Simons-like couplings. The world-volume couplings involve Abelian 1-form gauge fields in the bulk and possibly field strengths intrinsic to the brane. In many cases these couplings are the D-brane Chern-Simons terms present in string theory, while in other cases they are the interactions of axion domain walls with U(1) fields. Our arguments use the same logic and assumptions as the recent Festina Lente proposal (thus utilizing the properties of Nariai de Sitter black holes) and generalize it to extended objects, thereby providing a bottom-up set of constraints independent of any particular UV completion. We compare these bounds to the properties of (wrapped) D-branes in Type II string theory in the weak coupling limit, under the assumption that these properties are not modified significantly in de Sitter constructions. We find that all constraints are satisfied by D-branes, providing further evidence for the Festina Lente conjecture. For the particular case of 2-branes with Chern-Simons interactions we obtain a bound, which however can be evaded if the theory contains a light axion. Similarly, we find the bounds do not apply to axion domain walls due to the presence of the axion.

United Kingdom

Saquib Hassan

Georges Obied

John March-Russell

De Sitter space constraints on brane tensions and couplings

We study the dynamics and interactions of the solitonic domain walls that occur in realistic axion electrodynamics models including the Chern-Simons interaction, , between an axion ( ) of mass , and a massless U(1) gauge field, e.g. EM, interacting with strength = /4 with charged matter, e.g. electron-positron pairs. In particular, in the presence of a U(1) gauge-and-matter relativistic thermal plasma we study the friction experienced by the walls due to the Chern-Simons term. Utilizing the linear response method we include the collective effects of the plasma, as opposed to purely particle scattering across the wall (as is done in previous treatments) which is valid only in the thin wall regime that is rarely applicable in realistic cases. We show that the friction depends on the Lorentz- -factor-dependent inverse thickness of the wall in the plasma frame, ~ , compared to the three different plasma scales, the temperature , the Debye mass ~ $$ \sqrt{\alpha }T $$ , and the damping rate Γ ~ , and elucidate the underlying physical intuition for this behavior. (For friction in the thin-wall-limit we correct previous expressions in the literature.) We further consider the effects of long-range coherent magnetic fields that are possibly present in the early universe and compare their effect with that of thermal magnetic fields. We comment on the changes to our results that likely apply in the thermal deconfined phase of a non-Abelian gauge theory. Finally, we briefly discuss the possible early universe consequences of our results for domain wall motion and network decay, stochastic gravitational wave production from domain wall networks, and possible primordial black hole production from domain wall collapse, though a more complete discussion of these topics is reserved for a companion paper.

Gaurang Kane

Chern-Simons induced thermal friction on axion domain walls

We investigate the prospect of detecting the dark matter (DM) candidate in the three-loop radiative neutrino mass generation model extended with large electroweak multiplets of the Standard Model (SM) gauge group, at the future imaging atmospheric Cherenkov telescope known as the Cherenkov Telescope Array (CTA). We find that the addition of such large electroweak multiplets leads to a sizable Sommerfeld enhanced annihilation of the DM with an <math><mi>O</mi><mo>(</mo><mi>TeV</mi><mo>)</mo></math> mass, into the SM gauge bosons, which results in continuum- and line-like spectra of very high-energy (VHE) gamma rays, and therefore becomes observable for the CTA. We determine the viable models by setting the upper limit on the <math><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><msub><mo>)</mo><mi>L</mi></msub></math> isospin of the multiplets from the partial-wave unitarity constraints and the appearance of a low-scale Landau pole in the gauge coupling. Afterwards, by considering the continuum VHE gamma rays produced from the DM annihilation at the Galactic Center, we probe the parameter space of the model using the sensitivity reach of the CTA.

Bangladesh

Italy

Talal Ahmed Chowdhury

United States

Jahid Hossain

United Arab Emirates

Salah Nasri

Mahmud Ashraf Shamim

Probing the dark matter of a three-loop radiative neutrino mass generation model with the Cherenkov Telescope Array