We propose a thesis for the study of the scientific potential and technical feasibility of a Lunar Seismic and Gravitational Antenna (LSGA). LSGA is a response to the call of ideas of ESA for a Lunar Lander. It concerns the deployment of an engineered fiber distributed acoustic sensor system (EFDAS) on the lunar surface, in complementarity and projected increase of sensitivity, to the Very Broad Band VBBZ Farside Seismic Suite (VBBZ-FSS). The LSGA network will pursue in parallel a) geoscience goals (subsurface structure of the moon) b) a gravitational wave (GW) detection program, using the moon as detection body whose normal mode vibrations by GW are detected through a strain registering network c) a thermal and acoustic follow-up of the lunar surface and subsurface.
The proposal works in synergy and collaboration with two other proposals submitted to the ESA and NASA calls[1]. The responsibles of the thesis together with the coordinators of the 2 other proposals are currently organizing the large attendance, 1st International Workshop on Gravitational Wave detection at the Moon, at the European Gravitational Observatory (Pisa, Italy, 14-15 October)[2]. There are three structural advantages of deploying a GW network at the Moon: a) the moon has 3 orders of magnitude less seismicity than the Earth; b) the longer distance of moon to earth, and/or the parallax opportunities of the moon w.r.t earth, or the sun offers high resolution triangulation possibilities, for early warning of multimessenger events; c) The multi-band analysis of an inspiral/merger event will permit a much better precision of the inspiral/merger parameters. The LSGA detector concept is based on the scientific and technological potential of Engineered Fiber optic Distributed Acoustic Sensors (EFDAS), based on the phase shift of Rayleigh backscattered laser of a the EFDAS to detect induced strains from e.g. seismic, GW and acoustic waves, on chosen ("gauge") lengths of e.g. 10m, forming thus a large multi-sensor network. We propose the deployment of an antenna consisting of two 10 km long EFDAS fiber cables disposed in an L form interrogated by a central interrogator unit, using a narrowband laser light source. The main observable will be strain displacement along the horizontal axis, it will be thus complementary to the VBBZ deployment. It would be complemented with a temperature sensing (DTS) network. This configuration could exhibit one to two orders of magnitude better sensitivities from previous lunar deployments. The sensibilities of the fiber network will be compared to these of a passive Laser Reflector System, deployed at the edges of the L, detecting gravitational waves directly and not using the moon as a detection body, facing different but complementary systematics.

The thesis, would include:

1. a theoretical analysis part, a) using existing codes of the moon response and multiplication factor with respect to gravitational waves (Dyson, Ben-Menahem, Majstorovic)[3] updating them with new observations, including these of FSS; b) complementing and analyzing in detail studies on the sensitivities, directional acceptance and horizon distances of the LSGA deployment.

2. an experimental part studying the LSGA noise curves and sensitivity in an earth environment, parallel to Virgo/EGO at Cascina and also in comparison to an underground laser strainmeter (Kamioka Japan).

3. a technical part on the adaptation of the laser flight prototype of LISA-Pathfinder, and its instrumental and electronics accompaniments as well as the study of deployment issues of the fiber with a space rover or rocket and thermal protection of the fibers from moon temperature variations, including the search for an optimal site of deployment (e.g. close to Lunar Permanently Shadowed Regions)

Among the above themes, the work that will be finally included in the thesis will be discussed and agreed upon according to the knowledge and expertise of the candidate.

[1] Karan Jani and Abraham Loeb, arXiv:2007.08550v1 [gr-qc] 16 Jul 2020 and Jan Harms et al. The Astrophysical Journal, 910:1 (22pp), 2021 March 20

[2] https://indico.ego-gw.it/event/263/

[3] Freeman-Dyson (1969), 156:529– 540, 24. A. Ben-Menahem. (1983) II, Nuovo Cimento C, 6(1):49–71, 1983, J. Majstorovic et al. PHYSICAL REVIEW D 100, 044048 (2019)