Projects

Fundamental Symmetries

The reason why the Universe we observe today is dominated by matter over antimatter is still unknown and represents one of the big questions of modern physics. A tiny amount of combined charge conjugation (C) and parity (P) symmetry breaking must have driven the evolution of the Universe to the way we observe it today. The mystery though is that the fundamental interactions of particle physics do not contain enough CP-violation to explain the asymmetry we observe today. This observation points towards the existence of new physics containing new sources of CP-violation. Intrinsic electric dipole moments are a signature for CP-violation and the neutron provides an ideal system both experimentally and theoretically. After 65 years of attempts though we still have no experimental evidence of a neutron electric dipole moment and at the same time we still lack a precise theoretical determination.

The focus of this research thrust is to provide a precise calculation from first principles of the neutron electric dipole moment induced by new sources of CP-violation. To reach such a goal we are going to solve non-perturbatively the theory of strong interactions, Quantum Chromodynamics (QCD), defining it on a space-time lattice. To overcome the technical and conceptual difficulties that have hampered in the past this calculation, we will use a combination of innovative tools, such as the gradient flow to renormalize the CP- violating sources, and a novel QCD discretization, Stabilized Wilson Fermions, to control continuum limit and chiral extrapolation. The combination of these new ideas and technical developments will allow a precise calculation of the neutron electric dipole moment stemming from new CP-violating source, thus providing the theoretical result for the interpretation of future experimental measurements and a key step in the explanation of why the Universe is currently dominated by matter.

Θ-term

The so-called θ-term is a CP-violating contribution to the dynamics of the strong interactions. The parameter θ measure the amount of CP-violation. A non-vanishing θ can induce a contribution to the neutron electric dipole moment. The current experimental bounds restrict its value to be of the order of |θ| ∼ 10^-10, thus unnaturally small. This is the famous strong CP-problem: why is the θ-term so small? One possible answer comes from the existence of another particle, yet undiscovered, called the axion that could provide a dynamical explanation as to why θ vanishes.

BSM contributions to the EDM

The SM of particle physics predicts a neutron electric dipole moment (nEDM) 5-6 orders of magnitude smaller than the current experimental bound, but many beyond-the-Standard-Model (BSM) theories could potentially induce larger values for the nEDM still being consistent with the current experimental limit. Thus, the nEDM provides a unique window over BSM physics, that might explain the observed matter-antimatter asymmetry in the Universe.

Hadron Structure

Quantum Chromodynamics (QCD), the theory of strong interactions, comprehensively describes the interactions between quarks and gluons across a broad energy spectrum, including the binding mechanisms between these elementary particles. QCD is non-perturbative at low energies, presenting a challenge in applying perturbative methods for the analysis of hadron structures.
The study of hadron structure relies on the parton picture, where the dynamics of quarks and gluons are characterized by parton distribution functions (PDF).

The precision of QCD calculations is intricately tied to the accuracy of these PDFs, and this connection plays a crucial role in current measurements at the LHC. It will continue to be essential for future investigations at the EIC, HL-LHC, and LHeC. The current and future search for new physics depends heavily on the precision of the comparison between experimental data and theoretical predictions. This underscores the importance of a precise determination of PDFs.

The understanding of collider processes based on QCD factorization allows for the study of hadron structure using PDFs. Going beyond PDFs, generalized parton distributions (GPDs), and transverse-momentum-dependent distributions (TMDs) complement the 3-D description of hadrons. Although all the distribution functions are not directly measurable, they can be determined by factorizing the hard and soft parts of the cross-section of the process of interest.

Lattice QCD can offer a theoretical input for the determination of the PDFs and their evolution. The direct calculation of PDFs using lattice QCD poses particular challenges due to the Euclidean geometry and the light-cone dominance of the kinematics. The connection between PDFs and hadronic matrix elements, which are calculable in lattice QCD, is established through the moments of the PDFs.

In this research thrust, we propose a method that addresses both the theoretical and numerical challenges faced in the past, which hindered the calculation of moments of any order from lattice QCD.

Non singlet twist-2 operators

QCD factorization relates the moments of the structure functions and the moments of the parton distribution functions. The moments of structure functions are linear combinations of hadronic matrix elements of certain local operators with coefficients calculable in perturbation theory. The hadronic matrix elements are proportional to the moments of PDFs. In the context of deep inelastic scattering (DIS) kinematics, the leading contribution arises from local operators with the lowest twist, τ = d_O – n =2, where d_O is the physical dimension of the local operator and n is its spin. The calculation of the hadronic matrix elements have been restricted to just the first few moments because of theoretical and numerical challenges related to the breaking of rotational symmetry in a discrete lattice. The method we propose solves all these challenges and promises the possibility to a full reconstruction of the PDFS.

Graphic Design

Logos, merchandise and more. Anyone can create nice graphics. We think it’s better to create memorable ones.

Web Design

Custom web design for small businesses, we help you capture new audiences and increase your sales.

Content Creation

Want to attract people to your website? You have to have the best content in the world. That’s what we do.

About 95% of the observable mass in the Universe is a result of quarks binding into nucleons through the strong interactions of quantum chromodynamics (QCD). The slight mass difference (approximately 0.07%) between protons and neutrons is attributed to isospin symmetry breaking in the Standard Model. This breaking is due to differences in the masses and electric charges of down and up quarks. Despite the small magnitude of these effects, they play a crucial role in our comprehension of the Universe. For instance, the early Universe’s primordial abundance of light nuclear elements is highly sensitive to the neutron’s excess mass compared to the proton. Lattice QCD (LQCD) offers a fundamental approach to assess isospin-breaking effects in hadronic and nuclear processes. Several LQCD calculations have been conducted on the strong contribution to nucleon mass splitting, as well as electromagnetic corrections. While incorporating electromagnetism into Lattice QCD (LQCD) is theoretically uncomplicated, it poses practical challenges due to the long-range characteristics of electromagnetic (QED) interactions. In particular, these interactions result in finite-volume (FV) corrections following power-law patterns. Removing these corrections through extrapolation involves computationally demanding simulations conducted across multiple volumes. An analytical comprehension of the power-law finite-volume effects within such configurations has facilitated dependable extrapolations of the single hadron spectrum.

QEDM: massive photons on the lattice

Despite the effective use of existing techniques, there are compelling reasons to explore new methods. Achieving control over finite-volume (FV) modifications to light nuclear binding energies often necessitates exceptionally large volumes. Beyond the spectrum, precise knowledge of Quantum Electrodynamics (QED) modifications is essential for various quantities, such as corrections to hadronic matrix elements and charged particle scattering, both facing challenges in the infrared (IR) range. While Lattice QCD (LQCD) calculations employ multiple ultraviolet (UV) regulators, offering valuable checks on the continuum extrapolation of crucial quantities, incorporating multiple IR regulators is crucial for LQCD calculations involving QED. However, only a few formulations have been explored to date, with only one constructed using a local quantum field theory. Additionally, having computationally efficient methods to account for IR effects is desirable not only for lattice QCD+QED but also in scenarios where long-range Coulomb interactions are present. Motivated by these considerations, we illustrate the feasibility of an alternative IR regulator for lattice QCD+QED simulations: specifically, introducing a photon mass, denoted as m_γ.