The main goal of this project is to guarantee and strengthen the technological and scientific contributions of the IAC to LiteBIRD, a JAXAled space mission, currently in phase A and with launch planned for 2032. The ultimate goal of this mission is to constrain to unprecedented sensitivity levels (tensor-to-scalar ratio of r = 0.001) the expected B-mode signal in the polarization of the Cosmic Microwave Background produced by the background of gravitational waves produced during the inflation of the Universe. Detecting this signal is considered the most important challenge in Cosmology nowadays. Such a discovery would allow to confirm the inflationary scenario, one important piece of the LCDM model, and would open the door to investigate physical processes in an energy range (~10^16 GeV) orders of magnitude above the highest energies that can be reached in Earth-based laboratories like LHC. LiteBIRD aims to improve current constraints on the B-mode amplitude by a factor 10 and then is considered the flagship project in the field. Realizing its objective requires unprecedented detector sensitivity and also extraordinary control of systematics. This proposal will address some of the key issues needed to reach this scientific goal, in particular:
1) Development of the thermal monitoring and control system (TMCS) of the focal plane of the medium and high frequency telescopes (MHFTs). This work package, which falls under the responsibility of Spain, is essential to control to the required level gain variations driven by temperature fluctuations that would critically degrade the performance of the detectors. This project aims to continue, during the end of phase A and beginning of phase B, the activities that were funded by a previous project between October 2021 and March 2023. In particular:
* Consolidation of the technical requirements.
* Validation of the proposed temperature sensors and demonstration of the proposed key electronic functions of the TMCS by means of prototypes.
* Design of an electronic BreadBoard model implementing all the functionalities required to evaluate the performance of the temperature sensors.
* Consolidate the requirements of a cryogenic test-bench to validate the TMCS electronic models performance.
* Design of a cryogenic test-bench to demonstrate the performance of the TMCS development models.
2) Characterization and modelling of low-frequency Galactic foreground emission. Foreground emission is more intense and overshadows the primordial B-model signal, thence implying that a thorough modelling of their spectra is mandatory to be able to subtract and correct this signal. During this project we will make use of the recently released low-frequency QUIJOTE data, in combination with other datasets, to:
* Forecast the level of contamination introduced by polarized synchrotron emission in LiteBIRD data.
* Study the best methodology to correct this signal down to the required level.
* Forecast the ability of LiteBIRD data to deepen our understanding of the properties of the Anomalous Microwave Emission, in total intensity and in polarization.
3) Consolidation of the requirements on the calibration accuracy of different instrument parameters derived from top-level scientific requirements, and definition of the LiteBIRD on-sky calibration strategy of these parameters via realistic simulations of the telescope scanning strategy, noise and sky signals.
