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Carlos Munoz

Publications and source records attributed to Carlos Munoz.

At least 37 records · Page 2Linked to original sources
arXiv2015

Hunting physics beyond the standard model with unusual $W^\pm$ and $Z$ decays

Nonstandard on-shell decays of $W^\pm$ and $Z$ bosons are possible within the framework of extended supersymmetric models, i.e., with singlet states and/or new couplings compared to the minimal supersymmetric standard model. These modes are typically encountered in regions of the parameter space with light singlet-like scalars, pseudoscalars, and neutralinos. In this letter we emphasize how these states can lead to novel signals at colliders from $Z$- or $W^\pm$-boson decays with prompt or displaced multileptons/tau jets/jets/photons in the final states. These new modes would give distinct evidence of new physics even when direct searches remain unsuccessful. We discuss the possibilities of probing these new signals using the existing LHC run-I data set. We also address the same in the context of the LHC run-II, as well as for the future colliders. We exemplify our observations with the "$μ$ from $ν$" supersymmetric standard model, where three generations of right-handed neutrino superfields are used to solve shortcomings of the minimal supersymmetric standard model. We also extend our discussion for other variants of supersymmetric models that can accommodate similar signatures.

hep-ph↗
arXiv2014

Probing the $μν$SSM with light scalars, pseudoscalars and neutralinos from the decay of a SM-like Higgs boson at the LHC

The "$μ$ from $ν$" supersymmetric standard model ($μν$SSM) can accommodate the newly discovered Higgs-like scalar boson with a mass around 125 GeV. This model provides a solution to the $μ$-problem and simultaneously reproduces correct neutrino physics by the simple use of right-handed neutrino superfields. These new superfields together with the introduced $R$-parity violation can produce novel and characteristic signatures of the $μν$SSM at the LHC. We explore the signatures produced through two-body Higgs decays into the new states, provided that these states lie below in the mass spectrum. For example, a pair produced light neutralinos depending on the associated decay length can give rise to displaced multi-leptons/taus/jets/photons with small/moderate missing transverse energy. In the same spirit, a Higgs-like scalar decaying to a pair of scalars/pseudoscalars can produce final states with prompt multi-leptons/taus/jets/photons.

hep-ph↗
arXiv2014

Search for 100 MeV to 10 GeV gamma-ray lines in the Fermi-LAT data and implications for gravitino dark matter in the $μν$SSM

Dark matter decay or annihilation may produce monochromatic signals in the gamma-ray energy range. In this work we argue that there are strong theoretical motivations for studying these signals in the framework of gravitino dark matter decay and we perform a search for gamma-ray spectral lines from 100\,MeV to 10\,GeV with Fermi-LAT data. In contrast to previous line searches at higher energies, the sensitivity of the present search is dominated by systematic uncertainties across most of the energy range considered. We estimate the size of systematic effects by analysing the flux from a number of control regions, and include the systematic uncertainties consistently in our fitting procedure. We have not observed any significant signals and present model-independent limits on gamma-ray line emission from decaying and annihilating dark matter. We apply the former limits to the case of the gravitino, a well-known dark matter candidate in supersymmetric scenarios. In particular, the $R$-parity violating "$μ$ from $ν$" Supersymmetric Standard Model ($μν$SSM) is an attractive scenario in which including right-handed neutrinos solves the $μ$ problem of the Minimal Supersymmetric Standard Model while simultaneously explaining the origin of neutrino masses. At the same time, the violation of $R$-parity renders the gravitino unstable and subject to decay into a photon and a neutrino. As a consequence of the limits on line emission, $μν$SSM gravitinos with masses larger than about 5\,GeV, or lifetimes smaller than about $10^{28}$\,s, are excluded at 95% confidence level as dark matter candidates.

astro-ph.HE↗
arXiv2013

Constraints on WIMP Annihilation for Contracted Dark Matter in the Inner Galaxy with the Fermi-LAT

We derive constraints on parameters of generic dark matter candidates by comparing theoretical predictions with the gamma-ray emission observed by the Fermi-LAT from the region around the Galactic Center. Our analysis is conservative since it simply requires that the expected dark matter signal does not exceed the observed emission. The constraints obtained in the likely case that the collapse of baryons to the Galactic Center is accompanied by the contraction of the dark matter are strong. In particular, we find that for bb and τ+τ- or W+W- dark matter annihilation channels, the upper limits on the annihilation cross section imply that the thermal cross section is excluded for a Weakly Interacting Massive Particle (WIMP) mass smaller than about 700 and 500 GeV, respectively. For the μ+ μ- channel, where the effect of the inverse Compton scattering is important, depending on models of the Galactic magnetic field the exclusion of the thermal cross-section is for a WIMP mass smaller than about 150 to 400 GeV. The upper limits on the annihilation cross section of dark matter particles obtained are two orders of magnitude stronger than without contraction. In the latter case our results are compatible with the upper limits from the Galactic halo analysis reported by the Fermi-LAT collaboration for the case in which the same conservative approach without modeling of the astrophysical background is employed.

astro-ph.HE↗
arXiv2013

Probing the "$μ$ from $ν$" supersymmetric standard model with displaced multileptons from the decay of a Higgs boson at the LHC

The "$μ$ from $ν$" supersymmetric standard model ($μν$SSM) cures the $μ$-problem and concurrently reproduces measured neutrino data by using a set of usual right-handed neutrino superfields. Recently, the LHC has revealed the first scalar boson which naturally makes it tempting to test $μν$SSM in the light of this new discovery. We show that this new scalar while decaying to a pair of unstable long-lived neutralinos, can lead to a distinct signal with non-prompt multileptons. With concomitant collider analysis we show that this signal provides an unmistakable signature of the model, pronounced with light neutralinos. Evidence of this signal is well envisaged with sophisticated displaced vertex analysis, which deserves experimental attention.

hep-ph↗
arXiv2012

The $μν$SSM with an extra U(1)

The $μν$SSM solves the $μ$ problem of the MSSM and generates correct neutrino masses by simply using right-handed neutrinos. This mechanism implies that only dimensionless trilinear terms, breaking R-parity, are present in the superpotential. We present an extension of the $μν$SSM with an extra U(1) gauge symmetry. We use the extra U(1) charges of the matter fields to forbid the presence in the superpotential of renormalizable and non-renormalizable baryon number violating operators, the trilinear operator producing a domain wall problem, and bilinear operators such as the $μ$ term and the Majorana masses. We apply the anomaly cancellation conditions associated to the extra U(1), to constrain the values of the U(1) charges. We find that six assignments of the U(1) charges to the matter fields are viable, once extra matter is introduced. In particular, three generations of vector-like color triplets and $SU(2)_L$ doublets, as well as six Standard Model singlets are necessary. Electroweak symmetry breaking is viable in the model, with wide regions of the parameter space fulfilling the experimental constraints on the existence of a new gauge boson $Z'$. Neutrinos and the extra gaugino mix with the MSSM neutralinos, producing a generalized see-saw matrix that can reproduce the experimental results on neutrino masses. Finally, we have estimated the tree-level upper bound on the lightest Higgs mass, finding that it can be as large as about 120 GeV.

hep-ph↗
arXiv2012

Indirect Dark Matter Searches and Models

Indirect dark matter searches are briefly reviewed. Current experimental data from satellites and Cherenkov telescopes searching for antimatter and gamma rays in galactic and extragalactic regions, are compared with predictions from theoretical models of dark matter. The analysis is focused on WIMPs such as the neutralino and the sneutrino, and a superWIMP such as the gravitino, in several interesting supersymmetric models. In particular, the discussion is carried out in the context of R-parity conserving models such as the MSSM, the NMSSM, and an extended NMSSM, and the R-parity violating model $μν$SSM.

hep-ph↗
arXiv2011

The Higgs sector of the munuSSM and collider physics

The $μν$SSM is a supersymmetric standard model that accounts for light neutrino masses and solves the $μ$ problem of the MSSM by simply using right-handed neutrino superfields. Since this mechanism breaks R-parity, a peculiar structure for the mass matrices is generated. The neutral Higgses are mixed with the right- and left-handed sneutrinos producing 8$\times$8 neutral scalar mass matrices. We analyse the Higgs sector of the $μν$SSM in detail, with special emphasis in possible signals at colliders. After studying in general the decays of the Higges, we focus on those processes that are genuine of the $μν$SSM, and could serve to distinguish it from other supersymmetric models. In particular, we present viable benchmark points for LHC searches. For example, we find decays of a MSSM-like Higgs into two lightest neutralinos, with the latter decaying inside the detector leading to displaced vertices, and producing final states with 4 and 8 $b$-jets plus missing energy. Final states with leptons and missing energy are also found.

hep-ph↗
arXiv2010

Gamma-ray detection from gravitino dark matter decay in the $μν$SSM

The $μν$SSM provides a solution to the $μ$-problem of the MSSM and explains the origin of neutrino masses by simply using right-handed neutrino superfields. Given that R-parity is broken in this model, the gravitino is a natural candidate for dark matter since its lifetime becomes much longer than the age of the Universe. We consider the implications of gravitino dark matter in the $μν$SSM, analyzing in particular the prospects for detecting gamma rays from decaying gravitinos. If the gravitino explains the whole dark matter component, a gravitino mass larger than 20 GeV is disfavored by the isotropic diffuse photon background measurements. On the other hand, a gravitino with a mass range between 0.1-20 GeV gives rise to a signal that might be observed by the FERMI satellite. In this way important regions of the parameter space of the $μν$SSM can be checked.

hep-ph↗
arXiv2009

The $μν$SSM and gravitino dark matter

We consider the phenomenological implications of gravitino dark matter in the context of the $μν$SSM. The latter is an R-parity breaking model which provides a solution to the $μ$-problem of the MSSM and explains the origin of neutrino masses by simply using right-handed neutrino superfields. In particular, we analyze the prospects for detecting gamma rays from decaying gravitinos. Gravitino masses larger than 20 GeV are disfavored by the isotropic diffuse photon background measurements, but a gravitino with a mass range between $0.1 - 20$ GeV gives rise to a signal that might easily be observed by the FERMI satellite. Through this kind of analysis important regions of the parameter space of the $μν$SSM can be checked.

hep-ph↗
arXiv2008

Analysis of the parameter space and spectrum of the $μν$SSM

The $μν$SSM is a supersymmetric standard model that solves the $μ$ problem of the MSSM using the R-parity breaking couplings between the right-handed neutrino superfields and the Higgses in the superpotential, $λ_{i} \hat ν^c_i \hat H_d \hat H_u$. The $μ$ term is generated spontaneously through sneutrino vacuum expectation values, $μ=λ_i < \tilde ν^c_i>$, once the electroweak symmetry is broken. In addition, the couplings $κ_{ijk} \hat ν^c_i\hat ν^c_j\hat ν^c_k$ forbid a global U(1) symmetry avoiding the existence of a Goldstone boson, and also contribute to spontaneously generate Majorana masses for neutrinos at the electroweak scale. Following this proposal, we have analysed in detail the parameter space of the $μν$SSM. In particular, we have studied viable regions avoiding false minima and tachyons, as well as fulfilling the Landau pole constraint. We have also computed the associated spectrum, paying special attention to the mass of the lightest Higgs. The presence of right and left-handed sneutrino vacuum expectation values leads to a peculiar structure for the mass matrices. The most important consequence is that neutralinos are mixed with neutrinos, and neutral Higgses with sneutrinos.

hep-ph↗
arXiv2005

More about soft terms and FCNC in realistic string constructions

In realistic four-dimensional string constructions the presence of anomalous U(1)'s is generic. In addition, the associated Fayet-Iliopoulos contribution to the D-term can break the extra gauge symmetries. As a consequence, physical particles can appear combined with other states. We show that even if a three-generation standard-like model has originally flavour-independent soft scalar masses, the particle mixing contribution may generate non-universality among them. Thus FCNC effects which were apparently absent reappear. We also discuss the size of these contributions in an explicit model, and how they can be suppressed.

hep-ph↗
arXiv2004

Dark Matter Detection in the Light of Recent Experimental Results

The existence of dark matter was suggested, using simple gravitational arguments, seventy years ago. Although we are now convinced that most of the mass in the Universe is indeed some non-luminous matter, we still do not know its composition. The problem of the dark matter in the Universe is reviewed here. Particle candidates for dark matter are discussed with particular emphasis on Weakly Interacting Massive Particles (WIMPs). Experiments searching for these relic particles, carried out by many groups around the world, are also reviewed, paying special attention to their direct detection by observing the elastic scattering on target nuclei through nuclear recoils. Finally, we concentrate on the theoretical models predicting WIMPs, and in particular on supersymmetric extensions of the standard model, where the leading candidate for WIMP, the neutralino, is present. There, we compute the cross section for the direct detection of neutralinos, and compare it with the sensitivity of detectors. We mainly discuss supergravity, superstring and M-theory scenarios.

hep-ph↗
arXiv2003

Desperately Seeking the Standard Model

In the mid eighties string phenomenology started. Since then, its main objective, the search of the standard model, has not been accomplished yet. In this talk, on the ocassion of the 2nd International Conference on String Phenomenology in 2003, I will review this crucial issue.

hep-ph↗
arXiv2001

The Enigma of the Dark Matter

One of the great scientific enigmas still unsolved, the existence of dark matter, is reviewed. Simple gravitational arguments imply that most of the mass in the Universe, at least 90%, is some (unknown) non-luminous matter. Some particle candidates for dark matter are discussed with particular emphasis on the neutralino, a particle predicted by the supersymmetric extension of the Standard Model of particle physics. Experiments searching for these relic particles, carried out by many groups around the world, are also discussed. These experiments are becoming more sensitive every year and in fact one of the collaborations claims that the first direct evidence for dark matter has already been observed.

hep-ph↗
arXiv1997

Four-Dimensional Effective Supergravity and Soft Terms in M-Theory

We provide a simple macroscopic analysis of the four-dimensional effective supergravity of the Hořava-Witten M-theory which is expanded in powers of $κ^{2/3}/ρV^{1/3}$ and $κ^{2/3}ρ/V^{2/3}$ where $κ^2$, $V$ and $ρ$ denote the eleven-dimensional gravitational coupling, the Calabi-Yau volume and the eleventh length respectively. Possible higher order terms in the Kähler potential are identified and matched with the heterotic string corrections. In the context of this M-theory expansion, we analyze the soft supersymmetry-breaking terms under the assumption that supersymmetry is spontaneously broken by the auxiliary components of the bulk moduli superfields. It is examined how the pattern of soft terms changes when one moves from the weakly coupled heterotic string limit to the M-theory limit.

hep-th↗
arXiv1997

Supergravity Radiative Effects on Soft Terms and the $μ$ Term

We compute quadratically divergent supergravity one-loop effects on soft supersymmetry-breaking parameters and the $μ$ term in generic hidden sector supergravity models. These effects can significantly modify the matching condition for soft parameters at the Planck scale and also provide several new sources of the $μ$ term which are naturally of order the weak scale. We also discuss some phenomenological implications of these effects, particularly the violation of the scalar mass universality which may lead to dangerous FCNC phenomena, and apply the results to superstring effective supergravity models.

hep-ph↗