LV11331
CMB Imprints of Pseudoscalar Waves in the Early Universe
Massless pseudoscalar fields, which change sign under the parity
transformation, are often predicted by theories of new phsics including
string theory. These fields can have interactions with normal matter
which are sufficiently weak as to render them undetectable using
conventional particle physics techniques. However, cosmology provides us
with another powerful laboratory. A period of inflation in the early
universe would induce fluctuations in these pseudoscalar fields, which
then leave their imprint on the cosmic microwave background (CMB) photons
now being observed with ever-greater precision. This
provides a novel and very sensitive probe for the presence
of these fields in nature. This Letter desribes in detail how
the mere presence of pseudoscalar fluctuations leads to a diffusion of
photon polarization, transferring power from the gradient-like E-mode to
the curl-like B-mode of the CMB. This computation also determines the
current sensitivity limits from upper bounds on the B-mode, which show
significant prospects for improvement in the near future.
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LB12394BR
"Melting" metamaterials
Metamaterials are built from meta-molecules (compact electromagnetic resonators) in the same way nature builds crystals from atoms or molecules with distinct resonance features. The changes to the optical properties of metamaterials upon melting (i.e. during transition to a disordered state) were ingeniously investigated in this work by randomizing the positions of metamolecules in initially perfectly regular metamaterial arrays. Two antipode families of metamaterials emerged, exhibiting electromagnetic properties that depend or do not depend on disorder. This far-reaching difference is linked to the way the metamolecules interact with one another: in a strongly interacting ensemble of meta-molecules the order matters, while if the interaction is insignificant, "melting" does not affect electromagnetic properties of the medium.
