arXiv subjects

Clara Murgui

Publications and source records attributed to Clara Murgui.

35 records · Page 2Linked to original sources

arXiv2021

Baryonic Higgs and Dark Matter

We discuss the correlation between dark matter and Higgs decays in gauge theories where the dark matter is predicted from anomaly cancellation. In these theories, the Higgs responsible for the breaking of the gauge symmetry generates the mass for the dark matter candidate. We investigate the Higgs decays in the minimal gauge theory for Baryon number. After imposing the dark matter density and direct detection constraints, we find that the new Higgs can have a large branching ratio into two photons or into dark matter. Furthermore, we discuss the production channels and the unique signatures at the Large Hadron Collider.

hep-ph↗

arXiv2020

The role of right-handed neutrinos in $b \to c τ\barν$ anomalies

Motivated by the persistent anomalies reported in the $b\to cτ\barν$ data, we perform a general model-independent analysis of these transitions, in the presence of light right-handed neutrinos. We adopt an effective field theory approach and write a low-energy effective Hamiltonian, including all possible dimension-six operators. The corresponding Wilson coefficients are determined through a numerical fit to all available experimental data. In order to work with a manageable set of free parameters, we define eleven well-motivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements. The data exhibit a clear preference for new-physics contributions, and good fits to the data are obtained in several cases. However, the current measurement of the longitudinal $D^*$ polarization in $B\to D^*τ\barν$ cannot be easily accommodated within its experimental $1σ$ range. A general analysis of the three-body $B\to D τ\barν$ and four-body $B\to D^*(\to Dπ)τ\barν$ angular distributions is also presented. The accessible angular observables are studied in order to assess their sensitivity to the different new physics scenarios. Experimental information on these distributions would help to disentangle the dynamical origin of the current anomalies.

hep-ph↗

arXiv2020

The Higgs and Leptophobic Force at the LHC

The Higgs boson could provide the key to discover new physics at the Large Hadron Collider. We investigate novel decays of the Standard Model (SM) Higgs boson into leptophobic gauge bosons which can be light in agreement with all experimental constraints. We study the associated production of the SM Higgs and the leptophobic gauge boson that could be crucial to test the existence of a leptophobic force. Our results demonstrate that it is possible to have a simple gauge extension of the SM at the low scale, without assuming very small couplings and in agreement with all the experimental bounds that can be probed at the LHC.

hep-ph↗

arXiv2019

Axion Dark Matter, Proton Decay and Unification

We discuss the possibility to predict the QCD axion mass in the context of grand unified theories. We investigate the implementation of the DFSZ mechanism in the context of renormalizable SU(5) theories. In the simplest theory, the axion mass can be predicted with good precision in the range $m_a = (2-16)$ neV, and there is a strong correlation between the predictions for the axion mass and proton decay rates. In this context, we predict an upper bound for the proton decay channels with antineutrinos, $τ(p\to K^+ \barν) \lesssim 4 \times 10^{37} \text{ yr}$ and $τ(p \to π^+ \barν) \lesssim 2 \times 10^{36}\text{ yr}$. This theory can be considered as the minimal realistic grand unified theory with the DFSZ mechanism and it can be fully tested by proton decay and axion experiments.

hep-ph↗

arXiv2019

Gamma Lines from the Hidden Sector

We discuss the visibility of gamma lines from dark matter annihilation. We point out a class of theories for dark matter which predict the existence of gamma lines with striking features. In these theories, the final state radiation processes are highly suppressed and one could distinguish easily the gamma lines from the continuum spectrum. We discuss the main experimental bounds and show that one could test the predictions for gamma lines in the near future in the context of simple gauge theories for dark matter.

hep-ph↗

arXiv2019

The QCD Axion and Unification

The QCD axion is one of the most appealing candidates for the dark matter in the Universe. In this article, we discuss the possibility to predict the axion mass in the context of a simple renormalizable grand unified theory where the Peccei-Quinn scale is determined by the unification scale. In this framework, the axion mass is predicted to be in the range $m_a \simeq (3 - 13) \times 10^{-9} \ \rm{eV}$. We study the axion phenomenology and find that the ABRACADABRA and CASPEr-Electric experiments will be able to fully probe this mass window.

hep-ph↗

arXiv2019

Global fit to $b \to c τν$ transitions

We perform a general model-independent analysis of $b \to c τ\barν_τ$ transitions, including measurements of $\mathcal{R}_D$, $\mathcal{R}_{D^*}$, their $q^2$ differential distributions, the recently measured longitudinal $D^*$ polarization $F_L^{D^*}$, and constraints from the $B_c \to τ\barν_τ$ lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected $b \to cτ\barν_τ$ observables, such as the baryonic transition $Λ_b \to Λ_c τ\barν_τ$, the ratio $\mathcal{R}_{J/ψ}$, the forward-backward asymmetries ${\cal A}_\text{FB}^{D^{(*)}}$, the $τ$ polarization asymmetries $\mathcal{P}_τ^{D^{(*)}}$, and the longitudinal $D^*$ polarization fraction $F_L^{D^*}$. The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary $\mathcal{R}_{D^{(*)}}$ measurement by the Belle collaboration.

hep-ph↗

arXiv2019

Neutrino-Dark Matter Connections in Gauge Theories

We discuss the connection between the origin of neutrino masses and the properties of dark matter candidates in the context of gauge extensions of the Standard Model. We investigate minimal gauge theories for neutrino masses where the neutrinos are predicted to be Dirac or Majorana fermions. We find that the upper bound on the effective number of relativistic species provides a strong constraint in the scenarios with Dirac neutrinos. In the context of theories where the lepton number is a local gauge symmetry spontaneously broken at the low scale, the existence of dark matter is predicted from the condition of anomaly cancellation. Applying the cosmological bound on the dark matter relic density, we find an upper bound on the symmetry breaking scale in the multi-TeV region. These results imply we could hope to test simple gauge theories for neutrino masses at current or future experiments.

hep-ph↗

arXiv2019

On Anomaly-Free Dark Matter Models

We investigate the predictions of anomaly-free dark matter models for direct and indirect detection experiments. We focus on gauge theories where the existence of a fermionic dark matter candidate is predicted by anomaly cancellation, its mass is defined by the new symmetry breaking scale, and its stability is guaranteed by a remnant symmetry after the breaking of the gauge symmetry. We find an upper bound on the symmetry breaking scale by applying the relic density and perturbative constraints. The anomaly-free property of the theories allows us to perform a full study of the gamma lines from dark matter annihilation. We investigate the correlation between predictions for final radiation processes and gamma lines. Furthermore, we demonstrate that the latter can be distinguished from the continuum gamma ray spectrum.

hep-ph↗

arXiv2019

Leptophobic Dark Matter and the Baryon Number Violation Scale

We discuss the possible connection between the scale for baryon number violation and the cosmological bound on the dark matter relic density. A simple gauge theory for baryon number which predicts the existence of a leptophobic cold dark matter particle candidate is investigated. In this context, the dark matter candidate is a Dirac fermion with mass defined by the new symmetry breaking scale. Using the cosmological bounds on the dark matter relic density we find the upper bound on the symmetry breaking scale around 200 TeV. The properties of the leptophobic dark matter candidate are investigated in great detail and we show the prospects to test this theory at current and future experiments. We discuss the main implications for the mechanisms to explain the matter and antimatter asymmetry in the Universe.

hep-ph↗

arXiv2018

Dark Matter and The Seesaw Scale

We discuss the possibility to find an upper bound on the seesaw scale using the cosmological bound on the cold dark matter relic density. We investigate a simple relation between the origin of neutrino masses and the properties of a dark matter candidate in a simple theory where the new symmetry breaking scale defines the seesaw scale. Imposing the cosmological bounds, we find an upper bound of order multi-TeV on the lepton number violation scale. We investigate the predictions for direct and indirect detection dark matter experiments, and the possible signatures at the Large Hadron Collider.

hep-ph↗

arXiv2018

Seesaw Scale, Unification, and Proton Decay

We investigate a simple realistic grand unified theory based on the $SU(5)$ gauge symmetry which predicts an upper bound on the proton decay lifetime for the channels $p \to K^+ \barν$ and $p \to π^+ \barν$, i.e. $τ(p \to K^+ \barν) \lesssim 3.4 \times 10^{35}$ and $τ(p \to π^+ \barν) \lesssim 1.7 \times 10^{34}$ years, respectively. In this context, the neutrino masses are generated through the type I and type III seesaw mechanisms, and one predicts that the field responsible for type III seesaw must be light with a mass below 500 TeV. We discuss the testability of this theory at current and future proton decay experiments.

hep-ph↗

arXiv2017

Sterile Neutrinos and B-L Symmetry

We revisit the relation between the neutrino masses and the spontaneous breaking of the B-L gauge symmetry. We discuss the main scenarios for Dirac and Majorana neutrinos and point out two simple mechanisms for neutrino masses. In this context the neutrino masses can be generated either at tree level or at quantum level and one predicts the existence of very light sterile neutrinos with masses below the eV scale. The predictions for lepton number violating processes such as mu to e and mu to e gamma are discussed in detail. The impact from the cosmological constraints on the effective number of relativistic degree of freedom is investigated.

hep-ph↗

arXiv2017

Lepton Flavour Violation in Left-Right Theory

We investigate the predictions for lepton flavour number violating processes in the context of a simple left-right symmetric theory. In this context neutrinos are Majorana fermions and their masses are generated at the quantum level through the Zee mechanism using the simplest Higgs sector. We show that the right handed neutrinos are generically light and can give rise to large lepton number violating contributions to rare processes. We discuss the correlation between the collider constrains and the predictions for lepton number violating processes. We find that using the predictions for mu to e gamma and mu to e conversion together with the collider signatures one could test this theory in the near future.

hep-ph↗

arXiv2016

Renormalizable SU(5) Unification

We propose a simple renormalizable grand unified theory based on the $SU(5)$ gauge symmetry where the neutrino masses are generated at the quantum level through the Zee mechanism. In this model the same Higgs needed to correct the mass relation between charged leptons and down-type quarks plays a crucial role to generate neutrino masses. We show that in this model one can satisfy the constrains coming from the unification of gauge couplings and the mechanism for neutrino masses is discussed in detail. The predictions for proton decay are discussed in order to understand the testability at current and future experiments such as Hyper-Kamiokande. This simple theory predicts a light colored octet which could give rise to exotic signatures at the LHC.

hep-ph↗

arXiv2016

Simple Left-Right Theory: Lepton Number Violation at the LHC

We propose a simple left-right symmetric theory where the neutrino masses are generated at the quantum level. In this context the neutrinos are Majorana fermions and the model has the minimal degrees of freedom in the scalar sector needed for symmetry breaking and mass generation. We discuss the lepton number violating signatures with two charged leptons of different flavor and missing energy at the Large Hadron Collider in order to understand the testability of the theory.

hep-ph↗

arXiv2015

Pattern Formation in Populations with Density-Dependent Movement and Two Interaction Scales

We study the spatial patterns formed by a system of interacting particles where the mobility of any individual is determined by the population crowding at two different spatial scales. In this way we model the behavior of some biological organisms (like mussels) that tend to cluster at short ranges as a defensive strategy, and strongly disperse if there is a high population pressure at large ranges for optimizing foraging. We perform stochastic simulations of a particle-level model of the system, and derive and analyze a continuous density description (a nonlinear diffusion equation). In both cases we show that this interplay of scale-dependent-behaviors gives rise to a rich formation of spatial patterns ranging from labyrinths to periodic cluster arrangements. In most cases these clusters have the very peculiar appearance of ring-like structures, i.e., organisms arranging in the perimeter of the clusters, that we discuss in detail.

cond-mat.stat-mech↗