*Maurizio Consoli (INFN, Sezione di Catania, Italy)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: Wednesday, November 30, 2021

Time: 16h00

Abstract:

Spontaneous symmetry breaking is an essential ingredient of the Standard Model. While Goldstone bosons are well understood, still the ultimate dynamical origin of the phenomenon is not entirely clear. Given this uncertainty, one may wonder about the present view that the Higgs-field propagator has only one pole at 125 GeV. In fact, depending on the description of symmetry breaking, the effective potential, besides the mass scale describing its quadratic shape at the minima, could exhibit another mass scale associated with the zero-point energy, which determines its depth. Lattice simulations of the propagator are consistent with this two-mass structure and can be used to predict a new resonance around 700 GeV. In spite of its large mass, however, the heavier state would couple to longitudinal Ws with the same typical strength of the low-mass state and thus represent a relatively narrow resonance. In this way, such a hypothetical resonance would naturally fit with some excess of 4-lepton events observed by ATLAS around 680 GeV. Available CMS data in the same region, when grouped in bins of 30 GeV as done by ATLAS, are also consistent with this interpretation. Implications of this two-mass structure for radiative corrections will also be discussed.

References:

1) M. Consoli, Contribution to Veltman Memorial Volume,

Acta.Phys.Pol. B52 (2021) 763; arXiv:2106.06543 [hep-ph].

2) M. Consoli, L. Cosmai, Int. J. Mod. Phys. A35 (2020) 2050103;

arXiv:2006.15378 [hep-ph]

*Iveta Pimentel (Faculdade de Ciências – ULisboa)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: Wednesday, November 24, 2021

Time: 16h30

Abstract:

The Nobel Prize in Physics 2021, rewarded Giorgio Parisi for his revolutionary contributions to the understanding of complex systems. In his original work, he studied spin glasses which are magnetic systems with disorder and frustration. He developed a new method, using the replica trick, which describes complex systems and reveals hidden patterns. His discoveries have had great impact in physics, with the study of many different materials and phenomena, and in other different areas, such as biology, neuroscience, mathematics and computer science. In this seminar, I will present the study of spin glasses.

*Nuno Cardoso (CeFEMA)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: Wednesday, November 3, 2021

Time: 16h30

Abstract:

We study $I=0$ quarkonium resonances decaying into pairs of heavy-light mesons using static-static-light-light potentials from lattice QCD. To achieve this, we solve a coupled channel Schr\”odinger equation with a confined quarkonium channel and channels with a heavy-light meson pair to compute phase shifts and the poles for the lightest decay channel. We discuss our results for $S$, $P$, $D$ and $F$ wave states in the context of corresponding experimental results, in particular for $\Upsilon(10753)$ and $\Upsilon(10860)$.

*Hugo Terças (IPFN/IST)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: October 13, 2021

Time: 16h30

Abstract:

Axions are hypothetical particles, proposed as an extension of the Standard Model in an attempt to solve the strong CP problem in QCD. The Peccei-Quinn mechanism restores the CP symmetry by promoting the CP angle to a dynamical field – the axion – which is a pseudo-scalar field coupling to the theory. Because of their very long decay time (which is a consequence of the smallness of the CP angle), axions interact very weakly with electromagnetic fields. For that reason, axions are also very good candidates for dark matter, an issue that has attracted a great deal of attention recently. Experimental searches of axion and axion-like particles (ALPs) are based on the conversion between axions and photons. In vacuum, the amplitude of this process is extremely small, rendering detection schemes extremely ineffective. We argue that, in plasmas, the conversion probability increases by several orders of magnitude, as a consequence of the resonance in the axion-plasmon propagator. This fact makes enables the design of experimental configurations with projected sensitivities for a wide range of parameters. We also discuss some interesting in axion phenomenology in astrophysical and cosmological situations.

*Pedro Bicudo (CeFEMA)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: July 13th, 2021

Time: 15h00

Abstract:

We show how to compute from scratch, using undergraduate quantum mechanics techniques, the energy spectrum of the open (with Dirichlet boundary conditions) bosonic string with transverse degrees of freedom (the Nambu-Goto string) in the large distance case.

*José Emílio Ribeiro (CeFEMA)*

Place: Physics Seminar Room – Physics Building – 2nd flour

and Online(Zoom)

Date: June 28th, 2021

Time: 14h00

Abstract:

Equação de Dirac com conexões de spin, Vierbeins e Christoffel symbols: uma digressão com contas

*José Emílio Ribeiro (CeFEMA)*

Place: Online – Zoom

Date: Wednesday, October 21th, 2020

Time: 14h00

Abstract:

A metastable phase for QCD has important physical implications, since it may form vacuum bubbles that live enough so to be detectable experimentally, whereas an unstable vacuum instantly explodes.

As it is well known, due to chiral symmetry breaking, that there are at least two very different QCD vacua. At T=0, and in the true vacuum, the scalar and pseudo-scalar, or the vector and axial vector are not degenerate, and in the chiral limit, the pseudoscalar ground states become Goldstone bosons. As for the chiral invariant vacuum, it is unstable, decaying through an infinite number of scalar and pseudo-scalar tachyons.

On the contrary, QCD vacuum replicas, an infinite tower of finite volume, excited vacuum-like solutions, with energy densities lying between the true vacuum and the chiral invariant vacuum, have been predicted due to the non-linearity of the mass gap equation with a confining interaction. They possess real masses. We show the spectrum of quark-antiquark systems, studied both for the true vacuum and for the two first excited QCD replicas. The mass gap equation for the vacua and the Salpeter-RPA equation for mesons are solved for a simple chiral invariant and confining quark model approximating QCD in the Coulomb gauge.

We find their masses to be real, thus showing the QCD replicas in our approach may be indeed metastable.

Based on the publication: https://doi.org/10.1016/j.physletb.2020.135730

*Nikolai Scheuring (Institute of Organic Chemistry, University of Würzburg)*

Place: Online – Zoom

Date: Wednesday, July 29th, 2020

Time: 16h00-16h30

Abstract:

Recently, a board-shaped lead structure to obtain the biaxial nematic phase have been discovered with a promising aspect ratio and a broad nematic phase range. X-ray diffraction exhibited a scattering pattern which appeared to originate only from a rectangular form factor and solid-state NMR (relaxometry) revealed small biaxial clusters to be present in the nematic phase.[1] However, the material did not show any uniform alignment, even not in the electric field and consequently the biaxial phase could not be confirmed by Conoscopy.

This contribution will highlight the versatile synthesis of board shaped mesogens with a library of different peripheral decorations to optimize the aspect ratio, the alignment, the thermal stability and the interaction along the minor director. The nematogens are investigated by polarized optical microscopy, differential scanning calorimetry, X-ray scattering and Conoscopy. Preliminary results confirm the alignment of the nematogens in induced real biaxial nematic phases.

[1] M. Lehmann, S. Maisch, N. Scheuring, J. Carvalho, C. Cruz, P. J. Sebastião, R. Y. Dong, Soft Matter 2019, 15, 8496-8511.

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