Rasmi Enrique Hajjar Muñoz

Predoctoral Researcher at the Instituto de Física Corpuscular (CSIC-UV)

— About me —

Hi everyone! I am a Predoctoral Researcher in Neutrino Physics within the Instituto de Física Corpuscular (IFIC), a mixed centre between the Consejo Superior de Investigaciones Científicas (CSIC) and the University of Valencia (UV). I am a member of the SOM (Sabor y Origen de la Materia) group, and I give lectures as part of the Department of Theoretical Physics of the University of Valencia. I obtained the degree in Physics and the Master in Advanced Physics with specialization in Theoretical Physics at the UV.

I am a neutrino physicist interested in the role that the neutrino particle plays in Cosmology and Astroparticle Physics, where we can use neutrinos to disentangle some unknowns of the Universe as well as the different natural neutrino sources in order to probe properties of the neutrino particle. This makes my work a combination of coding (of course I mean debbugging) plus pen and paper calculations in order to understand the physics behind. In order to work on this fascinating field it is required a lot of knowledge in Quantum Mechanics, Cosmology, Astrophysics, Particle Physics, Statistics and Computer Programming. I know how to code in Python, C++, C, Mathematica, LaTeX and I learned html to set up this webpage.

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Me in New York visiting my brother.
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A wonderful landscape in Casinos, with the town in the distance.

I am from a small town in Spain called Casinos (with 0 units of casinos to answer your question), near Valencia, where I spent my whole life before moving to Valencia during the University years and after. I have also lived in another countries like the UK, Germany, Italy, USA and Denmark ranging from some months up to a year, and I loved the experience of discovering new cities and cultures, even though I had to take some Vitamine D to compensate the sun difference with Spain.

During those years I had the opportunity to learn English and Italian apart from my two mothertongues Catalan and Spanish. Actually, my town is the westmost town in Valencia in which Catalan is the main language, and I received my education in Catalan up to the Masters Degree, that was taught in English and Spanish.

Outside of physics, I enjoy playing tennis and I am a huge tennis fan. Wherever I go I bring my racquet with me just in case. I also like biking and hiking. I have also received musical education and I play the trombone, although I am a little bit out of practice right now.

— CV —

Here you can download my complete CV: Rasmi Hajjar CV

Education

Instituto de Física Corpuscular (CSIC-UV)

Ph.D. Student with contract FPU19/03348 of the Spanish Ministry of Universities

September 2021 - PRESENT, Valencia, Spain

Scuola Superiore Meridionale

Cosmology, Space Science and Space Technologies fellowship

November 2020 - September 2021, Napoli, Italy

University of Valencia

Masters Degree (M.Sc.) in Advanced Physics: Theoretical Physics

September 2019 - July 2020, Valencia, Spain

University of Leeds

Erasmus+ Programme Fellowship

September 2017 - July 2018, Leeds, UK

University of Valencia

Degree (B.Sc.) in Physics

September 2015 - July 2019, Valencia, Spain

Secondments

Niels Bohr Institute - University of Copenhagen

Research Secondment associated with the FPU19/03348 mobility grant EST24/00309

October 2024 - December 2024, Copenhagen, Denmark

KAVLI IPMU - The University of Tokyo

Research Secondment associated with the ASYMMETRY fellowship

July 2024 - August 2024, Kashiwa, Japan

Fermilab - Fermi National Accelerator Laboratory

Research Secondment associated with the ASYMMETRY fellowship

July 2023 - August 2023, Batavia, Illinois, USA

Center for Cosmology and AstroParticle Physics - The Ohio State University

Research Secondment associated with the FPU19/03348 mobility grant EST23/00231

May 2023 - July 2023, Columbus, Ohio, USA

Università degli Studi di Napoli Federico II

Research Secondment associated with the UV mobility grant UV-RI_MID-2515765

February 2023 - May 2023, Napoli, Italy

Teaching

Mentoring

Supervision of Master Thesis of Pietro Ghedini (University of Bologna)

Title: Growth of structures in non-standard Dark Energy models.

Co-supervision with Olga Mena and Silvia Pascoli.

— Research —

I am a neutrino physicsist interested in neutrino properties and probing fundamental physics of the universe using neutrinos.

You can find a brief summary of my main research fields and my contributions in the following:

Neutrino properties Astrophysical neutrinos Cosmological neutrinos Dark matter

Neutrino properties

The knowledge we have gained in the neutrino sector over the last few decades has allowed us to identify the first signature of physics beyond the Standard Model: neutrino masses.

Therefore is very important to constrain the neutrino parameters, and using natural neutrino sources is a good way and has proved that for some parameters it can give the dominant measurement.

I have performed studies in order to address the problems concerning both mass splittings: finding out the mass hierarchy using atmospheric neutrinos and resolving the solar mass splitting tension adding a measurement in the solar sector from a galactic supernova.

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How a future galactic SN explosion could contribute to the \(\Delta m_{21}^2\) tension using the HK detector. Figure from arXiv:2303.09369 [hep-ph].
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Predicted event rates of a future galactic SN explosion for a particular SN model. From here we can see that the oscillation pattern can give us information of the electron density that the neutrinos travel through, allowing us to perform a tomography study. Figure from arXiv:2307.09509 [hep-ph].

Astrophysical neutrinos

There are different astrophysical sources that emit neutrinos like Supernovae or AGNs. These neutrinos have a wide range of energies that depend on the astrophysical phenomena that produce them. With the knowledge gained in the neutrino sector we can use the emitted neutrinos as cosmic messengers.

One can use astrophyisical neutrinos in order to constrain properties of astrophysical objects like the Earth. In this regard I have performed research in order to understand how well we can reconstruct the Earth interior if the SN neutrinos travel through the Earth before reaching the detector.

Cosmological neutrinos

The role of neutrinos in cosmology if of utmost importance and it helps shaping the Universe in the way we know it. Understanding how the different properties of the neutrinos affect the evolution of the Universe becomes a mandatory task now that there is an emerging tension between cosmological upper bounds and oscillation lower limits on the sum of neutrino masses.

I have conducted research in order to understand the robustness of the cosmological neutrino mass measurement. In our work we have focused in understanding the separation between the cosmological background and perturbation evolution of the neutrinos, leading to the conclusion that cosmology is sensitive to the average energy density of neutrinos.

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CMB temperature anisotropy map.
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Dark matter predicted fluxes for some benchmark decay channels and lifetime values. It can be compared with the expected sensitivities of the future neutrino radio telescopes, the current IceCube HESE measurement and some expected neutrino flux contributions. Figure from arXiv:2103.03254 [hep-ph].

Dark matter

One of the most significant problems in particle physics is the nature of dark matter. Although we have evidence of its existence through various gravitational effects, its nature remains unknown despite the immense effort made by the community over the past decades.

In this regard, we should try to search for this dark matter anywhere since it could have any mass. Following a phenomeno-logical approach, we can attempt to find hints of dark matter decay or annihilation in the different astrophysical fluxes that reach Earth.

Focusing on very heavy dark matter, I have conducted research on forecasting the performance of future radio neutrino detectors in constraining the lifetime of decaying dark matter. Also, using ultra-high-energy gamma-rays I obtained complementary constraints with current measurements.

List of publications

Origin of cosmological neutrino mass bounds: background versus perturbations

T. Bertólez-Martínez, I. Esteban, R. Hajjar, O. Mena and J. Salvado, arXiv:2411.14524 [astro-ph.CO]

Redshift-space distortions corner interacting dark energy

Shedding light on the \(\mathbf{\Delta m_{21}^2}\) tension with supernova neutrinos

R. Hajjar, S. Palomares-Ruiz and O. Mena, Phys.Lett.B 854 (2024) 138719, arXiv:2307.09509 [hep-ph]

Earth tomography with supernova neutrinos at future neutrino detectors

R. Hajjar, O. Mena and S. Palomares-Ruiz, Phys.Rev.D 108 (2023) 8, 083011, arXiv:2303.09369 [hep-ph]

Constraints on heavy decaying dark matter with current gamma-ray measurements

M. Chianese, D.F.G. Fiorillo, R. Hajjar, G. Miele, N. Saviano, JCAP 11 (2021), 035, arXiv:2108.01678 [hep-ph]

Heavy decaying dark matter at future neutrino radio telescopes

M. Chianese, D.F.G. Fiorillo, R. Hajjar, G. Miele, S. Morisi, N. Saviano, JCAP 05 (2021), 074, arXiv:2103.03254 [hep-ph]

Neutrino mass ordering at DUNE: An extra \(\mathbf{\nu}\) bonus

C.A. Ternes, S. Gariazzo, R. Hajjar, O. Mena, M. Sorel and M. Tórtola, Phys.Rev.D 100 (2019) 9, 093004, arXiv:1905.03589 [hep-ph]

Current research is being supported by the Spanish grant FPU19/03348 of MICIU, by the Spanish MCIN/AEI/10.13039/501100011033 grants PID2020-113644GB-I00, PID2023-148162NB-C22 and PID2023-151418NB-I00, also by the European ITN project HIDDeN (H2020-MSCA-ITN-2019/860881-HIDDeN) and SE project ASYMMETRY (HORIZON-MSCA-2021-SE-01/101086085-ASYMMETRY) and by the Generalitat Valenciana grants PROMETEO/2019/083 and CIPROM/2022/69.

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— Contact —

Visiting address

IFIC office B-1-0, Carrer del Catedrátic José Beltrán Martinez, 2, 46980 Paterna, València

Email

If you want to contact me you can send an email to: