arXiv subjects

D. Hadjimichef

Publications and source records attributed to D. Hadjimichef.

At least 19 recordsLinked to original sources

arXiv2025

Brazilian Report on Dark Matter 2024

One of the key scientific objectives for the next decade is to uncover the nature of dark matter (DM). We should continue prioritizing targets such as weakly-interacting massive particles (WIMPs), Axions, and other low-mass dark matter candidates to improve our chances of achieving it. A varied and ongoing portfolio of experiments spanning different scales and detection methods is essential to maximize our chances of discovering its composition. This report paper provides an updated overview of the Brazilian community's activities in dark matter and dark sector physics over the past years with a view for the future. It underscores the ongoing need for financial support for Brazilian groups actively engaged in experimental research to sustain the Brazilian involvement in the global search for dark matter particles

hep-ph↗

arXiv2023

Internal heating mechanisms in neutron stars

The cooling of neutron stars (hereafter NS) has the potential to reveal important features of superdense matter. Their surface temperatures are known for a fair sample of NS with ages $\leq 10^{6} \, {\it{yr}}$, and with a few exceptions, can be accommodated by standard cooling mechanisms (neutrino+photon emission without internal heating). However, for the older objects it is necessary to consider some internal heating to explain surface temperatures higher than expected. We revisit in this paper the kinetic heating by fermionic dark matter, rotochemical heating and magnetic field decay. We found that NS slightly older than $\sim 10^{6} \, {\it{yr}}$ can be explained by them, but the older ``black widow'' systems are much hotter than the values predicted by these three mechanisms, pointing towards a yet unknown heating factor for old NS.

astro-ph.HE↗

arXiv2021

Pushing the limits of time beyond the Big Bang singularity: The branch cut universe

In this article we follow a previously developed theoretical approach, based in the tools of the singular semi-Riemannian geometry, to push the limits of time beyond the primordial spacetime singularity. By complexifying the Friedmann-Lemaître-Robertson-Walker (FLRW) metric and Friedmann's equations we model a branch cut universe, in which the cosmic FLRW metric scale factor is analytically continued to the complex plane, and becomes equivalent from a conceptual point of view of describing a hypothetical general metric of maximally symmetric and homogeneous superposed multiple universes.

gr-qc↗

arXiv2021

Pushing the limits of time beyond the Big Bang singularity: Scenarios for the branch cut universe

In this contribution we identify two scenarios for the evolutionary branch cut universe. In the first scenario, the universe evolves continuously from the negative complex cosmological time sector, prior to a primordial singularity, to the positive one, circumventing continuously a branch cut, and no primordial singularity occurs in the imaginary sector, only branch points. In the second scenario, the branch cut and branch point disappear after the realisation of the imaginary component of the complex time by means of a Wick rotation, which is replaced by the thermal time. In the second scenario, the universe has its origin in the Big Bang, but the model contemplates simultaneously a mirrored parallel evolutionary universe going backwards in the cosmological thermal time negative sector. A quantum formulation based on the WDW equation is sketched and preliminary conclusions are drawn.

gr-qc↗

arXiv2020

Matter-antimatter asymmetry and non-inertial effects

We investigate non-inertial effects on $CP$-violating processes using a model, based on the framework of quantum field theory in curved spacetimes, devised to account for the decay of accelerated particles. We show that the $CP$ violation parameter for the decay of accelerated kaons into two pions decreases very slightly as very high accelerations are achieved, implying decreased asymmetry between matter and antimatter in this regime. We discuss the relationship between these results and cosmological processes surrounding matter-antimatter asymmetry and argue that, due to the connection between non-inertial and thermal phenomena established by the Unruh effect, this kind of computation may prove useful in furthering the understanding of thermodynamical effects in curved spacetimes.

gr-qc↗

arXiv2020

Non-inertial effects on CP-violating systems

An analysis of accelerated kaon decays based on the Unruh effect shows a slight decrease in a CP-violation parameter for very high accelerations, as a consequence of the previously know increase in decay rates for non-inertial systems. Its consequences on the understanding of the relation between thermal and non-inertial phenomena are briefly discussed.

hep-ph↗

arXiv2020

Charmonium decay in the C3P0 Model

In this work, we use the $C^3P_{\,0}$ model to calculate the decay widths of the low lying charmonium $J^{PC}=1^{--}$ states, nominally $J/ψ(1S)$ and $ψ(2S)$, in the following common channels: $ρ\,π$, $ω\,η$, $ω\,η^\prime$, $K^{\ast +}\,K^-$, $K^{\ast 0}\,\bar{K}^0$, $ϕ\,η$, $ϕ\,η^\prime$.

hep-ph↗

arXiv2020

Ground Level Muon Flux Variation in a Cosmic Rays Simulation

The oscillatory movements of atmospheric air masses has been claimed to be the origin of the muon flux variation measured at the ground level. Using a cosmic ray toolkit (CORSIKA), we simulate cascade scenarios in a time scale of a year and show the dependence of the muon flux pattern with a proposed oscillatory model atmosphere.

hep-ph↗

arXiv2020

QCD effective charges and the structure function $F_{2}$ at small-$x$: Higher twist effects

We consider the effect of higher twist operators of the Wilson operator product expansion in the structure function $F_{2}(x,Q^{2})$ at small-$x$, taking into account QCD effective charges whose infrared behavior is constrained by a dynamical mass scale. The higher twist corrections are obtained from the renormalon formalism. Our analysis is performed within the conventional framework of next-to-leading order, with the factorization and renormalization scales chosen to be $Q^{2}$. The infrared properties of QCD are treated in the context of the generalized double-asymptotic-scaling approximation. We show that the corrections to $F_{2}$ associated with twist-four and twist-six are both necessary and sufficient for a good description of the deep infrared experimental data.

hep-ph↗

arXiv2020

Strong decays of strange quarkonia in a corrected 3P0 model

Extensively applied to both light and heavy meson decay and standing as one of the most successful strong decay models is the $^{3}P_{0}$ model, in which $q\bar{q}$ pair production is the dominant mechanism. In this paper we evaluate strong decay amplitudes and partial widths of strange $S$ and $D$ state mesons, namely $ ϕ(1020)$, $ϕ(1680) $, $ ϕ(2050) $, $ϕ_1 (1850) $, $ϕ_2 (1850) $ and $ ϕ_3 (1850) $, in the bound-state corrected $^{3}P_{0}$ decay model (C$^{3}P_{0}$). The C$^{3}P_{0}$ model is obtained in the context of the Fock-Tani formalism, which is a mapping technique.

hep-ph↗

arXiv2019

Brazilian Community Report on Dark Matter

This white paper summarizes the activities of the Brazilian community concerning dark matter physics and highlights the importance of financial support to Brazilian groups that are deeply involved in experimental endeavours. The flagships of the Brazilian dark matter program are the Cherenkov Telescope Array, DARKSIDE, SBN and LHC experiments, but we emphasize that smaller experiments such as DAMIC and CONNIE constitute important probes to dark sectors as well and should receive special attention. Small experimental projects showing the potential to probe new regions of parameter space of dark matter models are encouraged. On the theoretical and phenomenological side, some groups are devoted to astrophysical aspects such as the dark matter density profile while others explore the signature of dark matter models at colliders, direct and indirect detection experiments. In summary, the Brazilian dark matter community that was born not long ago has grown tremendously in the past years and now plays an important role in the hunt for a dark matter particle.

hep-ph↗

arXiv2017

Fine-tuning in scalar meson decay with bound-state corrections

The glueball-quarkonia mixture decay amplitude has been evaluated, in the literature, by diagrammatic techniques for drawing quark lines and the quark-gluon vertex. In this paper we use an alternative approach which consists in a mapping technique, the Fock-Tani formalism, in order to obtain an effective Hamiltonian starting from microscopic interactions. An extra effect is present in this formalism associated to the extended nature of mesons: bound-state corrections, which introduces an additional decay amplitude and sets a fine-tuning procedure for general meson decay calculations. The $f_0(1500) \to ππ$ channel shall be considered as numerical example of the procedure.

hep-ph↗

arXiv2015

Astrophysical aspects of milli-charged dark matter in a Higgs-Stueckelberg model

An extension of the Standard Model is studied, in which two new vector bosons are introduced, a first boson $Z'$ coupled to the SM by the usual minimal coupling, producing an enlarged gauge sector in the SM. The second boson $A'$ field, in the dark sector of the model, remains massless and originates a dark photon $γ'$. A hybrid mixing scenario is considered based on a combined Higgs and Stueckelberg mechanisms. In a Compton-like process a photon scattered by a WIMP is converted into a dark photon. This process is studied, in an astrophysical application obtaining an estimate of the impact on stellar cooling of white dwarfs and neutron stars.

hep-ph↗

arXiv2014

On the possibility of a 130 GeV gamma-ray line from annihilating singlet fermionic dark matter

There is evidence for a spectral line at $E_γ\approx 130$ GeV in the Fermi-LAT data that can be explained as dark mater particles annihilating into photons. We review a well known dark matter model that consists in a singlet Dirac fermion and a singlet scalar. The scalar implements spontaneous symmetry breaking in the dark sector, and is responsible for the communication between dark matter and Standard Model particles through a coupling to the Higgs. These interactions are supressed by the mixing between the scalar and the Higgs. Therefore, the singlet fermionic dark matter is naturally a weakly interacting massive particle (WIMP) and can explain the observed relic density. We show that this model cannot produce the signal identified in the Fermi-LAT data. Thus, we propose a modification in the model by introducing a new scalar multiplet that carries electric charge and couples to the singlet scalar. It enhances the annihilation into two photons and succeeds in producing the observed signal. We also discuss the resulting increase of the branching ratio of the $h\rightarrowγγ$ process, which is consistent with measurements from the CMS experiments.

hep-ph↗

arXiv2014

CP Violation in Dual Dark Matter

In this paper we study the consequences of extending dual symmetry (DuSy) to include a generic $C_μ$ vector field as a dual partner of the photon $A_μ$. A new combined field, the complex $Z^\prime_μ$, is obtained from $C_μ$ and $A_μ$. The promotion of dual symmetry to a local symmetry for $Z^\prime_μ$ implies in the inclusion of an extra complex vector field $W_μ$ with a complex gauge transformation. A dual dark matter (DM) Lagrangian ${\cal L}_{\rm DDM}$ is obtained from the general DuSy invariant Lagrangian ${\cal L}_{\rm DuSy}$. Our tentative conjecture is to interpret $W_μ$ as the actual weak interaction charged gauge boson $W^{\pm}_μ$, which leads us to speculate about a possible extra CP violation scenarios for future calculations.

hep-ph↗

arXiv2014

Effective Field Theory for Neutron Stars with Genuine Many-body Forces

The aim of our contribution is to shed some light on open questions facing the high density nuclear many-body problem. We focus our attention on the conceptual issue of naturalness and its role for the baryon-meson coupling for nuclear matter at high densities. As a guideline for the strengths of the various couplings the concept of naturalness has been adopted. In order to encourage possible new directions of research, we discuss relevant aspects of a relativistic effective theory for nuclear matter with natural parametric couplings and genuine many-body forces. Among other topics, we discuss in this work the connection of this theory with other known effective Quantum Hadrodynamics (QHD) models found in literature and how we can potentially use our approach to describe new physics for neutron stars. We also show some preliminary results for the equation of state, population profiles and mass-radius relation for neutron stars assuming local charge neutrality and beta equilibrium.

astro-ph.SR↗

arXiv2012

Searching for a dark matter coupling to the Standard Model with a Stueckelberg extension

We investigate a double extension to the Standard Model (SM). A first extension introduces, via minimal coupling, a massive $Z'$ boson. This enlarged SM is coupled to a dark matter sector through the Stueckelberg mechanism by a $A'$ boson. However, the $A'$ boson does not interact directly with the SM fermions. In our study, we found that the $A'$ is a massless photon-like particle in dark sector. Constraints on the mass for $Z'$ and corrections to $Z$ mass are obtained.

hep-ph↗

arXiv2012

Glueball-glueball potential in a constituent gluon model

In this work we use a mapping technique to derive in the context of a constituent gluon model an effective Hamiltonian that involves explicit gluon degrees of freedom. We study glueballs with two gluons using the Fock-Tani formalism. In the present work we calculate the glueball-glueball potential, in the context of the constituent gluon model, with gluon interchange.

hep-ph↗