Mariano Quirós

The group consists of Profs. Alex Pomarol and Eduard Masso, the postdoc Dr. Benedict von Harling and the IFAE researchers Dr. Oriol Pujolas and former ICREA Research Professor Mariano Quiros, now IFAE Emeritus Professor. The group activities are mainly in Beyond the Standard Model, Astro-Particle and Cosmology.

Generation of the baryon asymmetry in an extension of the Standard Model

M. Quiros, in collaboration with M. Carena (Fermilab and Enrico Fermi Institute and the University of Chicago) and Y. Zhang (Fermilab and Northwestern University) have explored the generation of the baryon asymmetry in an extension of the Standard Model where the lepton number is promoted to a $U(1)^\prime$ gauge symmetry with an associated $Z^\prime$ gauge boson. This is based on a novel electroweak baryogenesis mechanism first proposed by us in Ref. [1]. Extra fermionic degrees of freedom - including a fermionic dark matter $\chi$- are introduced in the dark sector for anomaly cancellation. Lepton number is spontaneously broken at high scale and the effective theory, containing the Standard Model, the $Z^\prime$ gauge boson, the fermionic dark matter, and an additional complex scalar field $S$, violates CP in the dark sector. The complex scalar field couples to the Higgs portal and is essential in enabling a strong first order phase transition. Dark CP violation is diffused in front of the bubble walls and creates a chiral asymmetry for $\chi$, which in turn creates a chemical potential for the Standard Model leptons. Weak sphalerons are then in charge of transforming the net lepton charge asymmetry into net baryon number. We explore the model phenomenology related to the leptophilic $Z^\prime$, the dark matter candidate, the Higgs boson and the additional scalar, as well as implications for electric dipole moments. We also discuss the interesting case when baryon number $U(1)_B$ is promoted to a gauge symmetry, and discuss electroweak baryogenesis and its corresponding phenomenology, for which the allowed parameter space is shown in Fig.~1.
Figure 1: Scan over the model parameters to find points that allow for successful EWBG (blue points). We show various experimental constraints by the correspondingly labeled shaded regions, in the gauged $U(1)_B$ model.

possibility that the existence of a (super) heavy Kaluza-Klein resonance could be detected at future gravitational interferometers as LISA and ET

M. Quiros, in collaboration with E. Megias (University of Granada) and G. Nardini (University of Stavanger, Norway) have considered the possibility that the existence of a (super) heavy Kaluza-Klein resonance could be detected at future gravitational interferometers as LISA and ET through the stochastic gravitational waves produced by the holographic radion confinement/deconfinement first order phase transition. We systematically study the holographic phase transition of the radion field in a five-dimensional warped model which includes a scalar potential with a power-like behavior. We consider Kaluza-Klein (KK) resonances with masses at the TeV scale or beyond. It turns out that the present and forthcoming gravitational wave observatories can probe scenarios where the KK resonances are very heavy. Current aLIGO data already rule out vector boson KK resonances with masses in the interval $\sim (1−10)\times 10^5$ TeV. Future gravitational experiments will be sensitive to resonances with masses $\sim 10^5$ TeV (LISA),$10^8$ TeV (aLIGO Design) and $10^9$ TeV (ET). The final results are summarized in Fig.~2.
Figure 2: Parameter reach in the plane for SGWBs in the regimes $\Omega_{\GW}^{\rm env}$ (regions inside dotted borders) and $\Omega_{\GW}^{\rm sw}$ (regions inside dashed borders). Diagonal strips are for $\rho = 1$,TeV (left set) and $\rho = 100$,TeV (right set). Regions inside the areas labeled aLIGO O2 and BBN are in tension with current data.

Other activities in 2020

M. Quiros and A. Delgado (University of Notre Dame, Indiana, USA) have explored the possibility, in the contextof the Minimal Supersymmetric extension of the Standard Model (MSSM), where the Higgsino plays the role of DM, in theories where supersymmetry breaking is transmitted by gravitational interactions at the unification scale $M\simeq 2×10^{16}$ GeV.We have focussed our work in the search of “light” supersymmetric spectra, which could be at reach of present and/or future colliders, in models with universal and non-universal Higgs and gaugino Majorana masses. The lightest supersymmetric particles of the spectrum are, by construction, two neutralinos and one chargino, almost degenerate, with a mass $\sim 1.1$ TeV, and a mass splitting of a few GeV. Depending on the particular scenario the gluino can be at its experimental mass lower bound $\sim 2.2$ TeV; in the squark sector, the lightest stop can be as light as $\sim 1.6$ TeV, and the lightest slepton, the right-handed stau, can have a mass as light as 1.2 TeV. The lightest neutralino can be found at the next generation of direct dark matter experimental searches. In the most favorable situation, the gluino, with some specific decay channels, could be found at the next run of the Large HadronCollider (LHC), and the lightest stop at the High-Luminosity LHC run.

B. von Harling, A. Pomarol and O. Pujolas showed that LIGO-Virgo observatories provide a novel probe of the QCD axion, through the gravitational wave background generated during the cosmological Peccei-Quinn transition. Indeed, first order phase transitions at a temperature around $10^9$GeV can be probed by LIGO-Virgo and we could identify several scenarios with sufficient supercooling that the signal is detectable. This motivates i) the search for these signals gravitational wave data and ii) a better understanding of the strong first order transition limit.

O. Pujolas with PhD student J. Olle have studied ‘oscillons’ - the non-topological solitons that appear quite generically in scalar theories with attractive self-interactions such as in axion models. Oscillons are localized bound states of many axions, with very large total mass concentrated in a few Compton radii, and their lifetime can be extremely large, up to $10^8$ oscillations, depending on the model. Moreover, they are attractor configurations in this type of models and they are spontaneously formed even if starting with a completely homogeneous but time-dependent axion background. We studied mainly two aspects of oscillons: i) their long lifetimes in well motivated axion ‘monodromy’ models and ii) their phenomenological impact in models ultra-light Dark Matter, where the effect of the scalar self interaction was neglected before.

O. Pujolas with PhD student V. Cancer-Castillo has studied the non-linear elastic response of solid materials from the perspective of modern field theory techniques. We used Effective Field Theory of solids to obtain very general constraints (bounds) among the observables that characterize the nonlinear response. We have also used AdS/CFT methods to study the special case presented by materials with scale invariance.

A. Pomarol, together with T. Gherghetta, V. V. Khoze and Y. Shirman, have calculated a new contribution to the axion mass arising from gluons propagating in a 5th dimension at high energies. This causes 5D small instantons to enhance the axion mass in a way that does not spoil the axion solution to the strong CP problem. Moreover this enhancement can be much larger than the usual QCD contribution from large instantons, although it requires the 5D gauge theory to be near the non-perturbative limit.

A. Pomarol, together with P. Baratella and C. Fernandez (PhD student of A. Pomarol), have used on-shell amplitude methods to derive a simple formula to obtain the anomalous dimensions of higher-dimensional operators from a product of tree-level amplitudes, with no need of loop calculations. They showed how this works for dimension-6 operators of the Standard Model, providing explicit examples of the simplicity, elegance and efficiency of the method. Many anomalous dimensions were calculated from the same Standard Model tree-level amplitude, displaying the attractive recycling aspect of the on-shell method. With this method, it was possible to relate anomalous dimensions that in the Feynman approach arise from very different diagrams, and obtain non-trivial checks of their relative coefficients.

B. von Harling, E. Mass'o and M. Quiros together with Ph.D. student Y. Cado, have shown that the baryon asymmetry of the Universe can be explained in models where the Higgs couples to the Chern-Simons term of the hypercharge group. This single framework makes use of the relaxation of the Higgs towards the minimum of its potential after inflation, the subsequent helical magnetic field production, and the chiral anomaly in the Standard Model.

B. von Harling, together with S. Bruggisser, O. Matsedonskyi and G. Servant have studied symmetry non-restoration in Composite Higgs models. New elementary fermions are introduced which linearly mix with operators of the Composite Higgs sector and lead in the confined phase to elementary-composite mixed states whose mass depends on the Higgs VEV. Some of these states become light for large Higgs VEVs. The thermal correction to the Higgs potential from these fermions then has a minimum around the Higgs VEV for which the fermion masses vanish. For n > O(few) new fermions, this thermal correction can dominate in the thermal Higgs potential, leading to a high-temperature minimum at a large Higgs VEV. Electroweak symmetry is then already broken for temperatures significantly above the electroweak scale. This in particular opens up parameter space for successful electroweak baryogenesis in Composite Higgs models.