Description
Chair: Savvas Nesseris
Quantum fluctuations created during cosmic inflation act as seeds of all structure in the universe. The strongest fluctuations lead to the formation of primordial black holes, a dark matter candidate. I present a study where these fluctuations are analyzed numerically within the framework of stochastic inflation. This method allows us to probe nonperturbative effects and include backreaction...
We revisit the two real singlet extension of the Standard Model with a $Z_2\times Z_2^\prime$ symmetry. One of the singlet scalars $S_2$, by virtue of an unbroken $Z_2^\prime$ symmetry, plays the role of a stable dark matter candidate. The other scalar $S_1$, with spontaneously broken $Z_2$-symmetry, mixes with the SM Higgs boson and acts as the scalar mediator. We analyze the model by putting...
Pulsar magnetospheres admit non-stationary vacuum gaps that are characterized by non-vanishing $\bf {E \cdot B}$. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy is set by the gap oscillation frequency. The density of axions produced in a gap can be several orders of magnitude greater than the...
Axions are a natural consequence of the Peccei-Quinn mechanism, the most compelling solution to the strong-CP problem. Similar axion-like particles (ALPs) also appear in a number of possible extensions of the Standard Model, notably in string theories. Both axions and ALPs are very well motivated candidates for Dark Matter, and in addition, they would be copiously produced at the sun’s core. A...
In this talk I will discuss a simple model of maximal axion misalignment. Maximally-misaligned axions with masses larger than 10^{-22} eV constitute an attractive DM candidate with interesting phenomenology. On the other hand, maximally-misaligned axions with masses m=O(1-100)H_0 generically behave as dark energy with a decay constant that can take values well below the Planck scale, avoiding...
In Twin Higgs models which contain the minimal particle content required to address the little hierarchy problem (i.e. fraternal models), the twin tau has been identified as a promising candidate for dark matter. In this class of scenarios, however, the elastic scattering cross section of the twin tau with nuclei exceeds the bounds from XENON1T and other recent direct detection experiments. In...
We revise cosmological mass bounds on hadronic axions in low-reheating cosmological scenarios, with a reheating temperature $T_{\rm RH}\le 100$ MeV, in light of the latest cosmological observations. In this situation, the neutrino decoupling would be unaffected, while the thermal axion relic abundance is suppressed. Moreover, axions are colder in low-reheating temperature scenarios, so that ...