# BSM-Astro/Cosmo

## The group consists of Profs. Alex Pomarol, and Eduard Masso, the Beatriz Galindo Distinguished Researcher Diego Blas, the IFAE researchers Dr. Oriol Pujolas and former ICREA Research Professor Mariano Quiros, now IFAE Emeritus Professor as well as the postdocs Dr. Ricardo Z. Ferreira, Dr. Benedict von Harling, Dr. L. delle Rose, Dr. Evangelos Sfakianakis, Dr. Ville Vaskonen, Dr. R. Vicente, Dr. G. Zahariade. The group activities are mainly in Beyond the Standard Model, Astro-Particle and Cosmology.

M. Quiros, in collaboration with A. Delgado (University of Notre Dame, Indiana, USA), E. Arganda and R. A. Morales (IFT/CSIC/UAM, Madrid) have considered the experimental detection at the LHC of gluinos [3,5] and squarks [1] in the cases where the Higgsino is the Lightest Supersymmetric Particle and constitutes the main, or part of the, component of Dark Matter.

M. Quiros, in a collaboration with A. Delgado [10] has explored the possibility of a $\sim$1 TeV Higgsino Dark Matter in the MSSM, consistently with the correct prediction of the Higgs mass and a correct electroweak symmetry breaking. The MSSM parameter space is considerably narrowed.

M. Quiros, in collaboration with E. Megias (University of Granada, Spain) has considered a solution to the hierarchy problem, based on a five-dimensional theory, where new physics are not isolated resonances but instead a continuum of states with masses starting from a TeV mass gap. This solution can easily evade many negative results from experimental detection. This line of research gave rise to the publications in Refs. [2,4,6,12].

M. Quiros, in collaboration with R. Escribano, M. Mendizabal and E. Royo (IFAE/AUB) has considered the possibility that new physics is constitued by broad resonances, for which experimental detections loose sensitivity, Ref. [9]. This case has been exemplified with the Randall Sundrum theory where KK gluons are very broad, stemming from a top sector very much localized toward the IR brane, where the KK modes are localized too, and thus with enhanced couplings.

M. Quiros, in collaboration with E. Megias and G. Nardini (University of Stavanger, Norway, and LISA Cosmology Working Group) have considered the predictions for detection of heavy KK resonances, by means of the Stochastic Background of Gravitational Waves generated at the confinement/deconfinement first order phase transition of the radion/dilaton. The bottom line, Refs. [7,12], is that resonances much above the TeV scale could be detected at the interferometers aLIGO Design, LISA and ET.

D. Blas, in collaboration with A. Jenkins (King’s College London, KCL) proposed a novel method to detect gravitational waves in a band hardly accessible by any other observation in [13,14]. Furthermore, this band, between LISA and PTA frequency bands, is full of possible signals from the early universe, whose study is possible only by the methods proposed in [13,14].

D. Blas, in collaboration with J. Alvey (U. Amsterdam), N. Sabti (King’s College London, KCL), M. Escudero (TUM) and M. Fairbairn updated their bounds on MeV dark matter using the recent results by the experiment LUNA [15].

D. Blas participated in the study of the Science Interpretation Working Group of the LISA mission [16] where it was determined the implication of the different proposed configurations for the LISA mission (a ESA/NASA mission to search for gravitational waves in space) for fundamental physics. Our results show that even if all configurations will access new interesting phenomena, the most ambitious one out-stands in terms of scientific return.

D. Blas, in collaboration with L. Badurina (KCL) and C. McCabe (KCL) studied the realistic bounds of current atom interferometers in the search of dark matter of ultralight mass [17]. In particular, they corrected previous estimates by taking into account the proper approximations for current detectors, not clarified before. The results are the first realistic prospects for these detectors, which will still be able to explore a new area of dark matter parameter space.

D. Blas, in collaboration with his PhD student N. Sabti (KCL) and his collaborator J. B. Mu~noz suggested a new observable to study the composition of the universe at times and scales currently hard to access [18,19]. With this method, they were able to measure cosmological parameters, as the typical size of overdensities at Mpc scale for the first time with precision. Since many models of dark matter alter this observable, the expectation is that further data and developments will make of this new observable a robust method to explore the universe.

D. Blas, in collaboration with a team of 6 more colleagues, determined how to use superconducting radiofrequency cavities to look for gravitational waves of frequencies in the GHz band [20]. These signals are of wavelengths which do not affect standard detectors, and their search represents a challenging problem. Our results show how to recycle experiments looking for dark matter for this purpose.

D. Blas, in collaboration with a team of 8 more colleagues, used the data of polarization of pulsars from PPTA and the Quijote experiment (lead by some of the authors) and performed the most detailed and constraining analysis to search for ultra-light dark matter pseudo-scalar particles through their effect on the polarization of the pulsar signal. The results are the first robust bound with this observable and rule out a significant region of dark matter at ultra light masses.

A. Pomarol in collaboration with T. Gherghetta has studied small instantons in weakly-gauged holographic models. They have found non-trivial UV localized instanton-anti-instanton solutions of the Yang-Mills equations where the topological charges annihilate in the AdS bulk. These analytic solutions arise from a 5D conformal transformation of the uplifted 4D instanton. This analysis has revealed unexpected nonperturbative configurations of Yang-Mills theories when they interact with strongly-coupled CFTs.

A. Pomarol in collaboration with Joan Elias Miro, Clara Fernandez and Mehmet Asim Gumus have analyzed lepton flavor violating processes generated via dimension-six operator mixing up to the two-loop level. They have used on-shell amplitude techniques, which make transparent many selection rulesand allow to calculate anomalous dimensions of SM EFT operators from the product of tree-level amplitudes, even for two-loop renormalization group mixings. They illustrate the importance of the EFT approach in models with extra vector-like fermions.

A. Pomarol in collaboration with Luigi Delle Rose and Benedict von Harling have showed how to calculate the contributions to Wilson Coefficients using On-Shell methods. They have applied these techniques to the one-loop calculation of g−2 and Hγγ showing how finite contributions can be obtained from the product of tree-level amplitudes. In certain cases, due to a parity symmetry of these amplitudes, the total contribution adds up to zero, as previously found in the literature. The method allows to search for new natural zeros, as well as to obtain non-zero contributions in a straightforward way.

O. Pujolas in collaboration with J. Olle and F. Rompineve have examined the longevity of oscillons, the bound states that appear in scalar theories with attractive self-interactions. The features of the scalar potential behind enhanced lifetimes were identified. A new numerical method was introduced to simulate time evolution for extremely long times. Our work shows that oscillons formed in the early Universe can be stable on cosmological time scales and thus are relevant for dark matter.

O. Pujolas in collaboration with M. Lewicki (Warsaw U.) and V. Vaskonen have shown that in models with strong supercooling, thermal inflation generically can end either by bubble nucleation and percolation or simply by the growth of quantum fluctuations. The stochastic gravitational wave background generated in either case provides an observable signal in almost the entire parameter space, and the shape of the gravitational wave spectrum can be used to distinguish which of the two escape mechanisms took place.

O. Pujolas in collaboration with V. Vaskonen and H. Veermäe have study the prospects of future GW detectors to probe Primordial Black Holes (PBHs), paying particular attention to subsolar mass PBHs. We considered GW signals from individual PBH binaries, the stochastic GW background generated by unresolvable binaries and nearly monochromatic continuous GWs from PBH binaries within the Milky Way DM halo. Across a broad mass range, future GW interferometers will probe the PBH abundance with higher sensitivity than any currently existing experiment.

O. Pujolas in collaboration with A. Romero-Rodriguez, M. Martinez, M. Sakellariadou (King’s Coll. London) and V. Vaskonen have performed a Bayesian search for the stochastic gravitational wave background induced by large enough scalar perturbations in the LIGO-Virgo third observing run. We find no evidence for such a background in the data. This places upper limits on the amplitude of curvature power spectrum that are more stringent than those arising from BBN or the CMB. Constraints from LIGO and Virgo, at their design sensitivity, and from the Einstein Telescope will compete with those arising from the abundance of PBHs.

R.Z. Ferreira in collaboration with A. Notari and F. Rompineve have performed for the first time a dedicated analysis of the cosmological constraints on the DFSZ axion. Using the latest Planck and BAO data they studied how the constraints on the axion mass depend on the axion coupling to pions and pointed out the importance of the coupling to leptons, which has not been considered in previous studies. They have also excluded part of the parameter space that was able to explain the recent excess seen in the Xenon 1T experiment.

R.Z. Ferreira in collaboration with C. Heissenberg have shown how the presence of asymptotic symmetries, supertranslations and superrotations, affect non-trivially the Bogolyubov coefficients associated with Hawking’s radiation. This study corrected the previous literature on supertranslations and expanded the analysis to superrotations for the first time. It also provided raised some interesting questions about the role of these symmetries in the black hole evaporation process.

R.Z Ferreira in collaboration with F. Arias-Aragon, F. D’Eramo, L. Merlo and A. Notari, completed the study of thermal axion production across the electroweak scale by providing a smooth and continuous treatment through the two phases. They have focused on both flavor conserving and violating couplings to third generation quarks and have shown that the correction to the effective number of relativistic degrees of freedom is within the sensitivity of future CMB-S4 surveys.