1,535 research outputs found
CB damping of primordial gravitational waves and the fine-tuning of the CB temperature anisotropy
Damping of primordial gravitational waves due to the anisotropic stress
contribution owing to the cosmological neutrino background (CB) is
investigated in the context of a radiation-to-matter dominated Universe.
Besides its inherent effects on the gravitational wave propagation, the
inclusion of the CB anisotropic stress into the dynamical equations also
affects the tensor mode contribution to the anisotropy of the cosmological
microwave background (CB) temperature. Given that the fluctuations of
the CB temperature in the (ultra)relativistic regime are driven by a
multipole expansion, the mutual effects on the gravitational waves and on the
CB are obtained through a unified prescription for a
radiation-to-matter dominated scenario. The results are confronted with some
preliminary results for the radiation dominated scenario. Both scenarios are
supported by a simplified analytical framework, in terms of a scale independent
dynamical variable, , that relates cosmological scales, , and the
conformal time, . The background relativistic (hot dark) matter
essentially works as an effective dispersive medium for the gravitational waves
such that the damping effect is intensified for the Universe evolving to the
matter dominated era. Changes on the temperature variance owing to the
inclusion of neutrino collision terms into the dynamical equations result into
spectral features that ratify that the multipole expansion coefficients
's die out for .Comment: 24 pages, 8 figure
-symmetric effects in measurement-based quantum thermal machines
Measurement-based quantum thermal machines are fascinating models of
thermodynamic cycles where measurement protocols play an important role in the
performance and functioning of the cycle. Despite theoretical advances,
interesting experimental implementations have been reported. Here we move a
step further by considering in this class of cycle -symmetric
non-Hermitian Hamiltonians and their implications in quantum thermal machines
fueled by generalized measurements. We present theoretical results indicating
that -symmetric effects and measurement protocols are related
along the cycle. Furthermore, tuning the parameters suitably it is possible to
improve the power output (engine configuration) and the cooling rate
(refrigerator configuration), operating in the Otto limit, in a finite-time
cycle that satisfies the quantum adiabatic theorem. Our model also allows
switching the configuration of the cycle, engine, or refrigerator, depending on
the strength of the measurement protocol
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