arXiv subjects

C. Muñoz

Publications and source records attributed to C. Muñoz.

At least 37 records · Page 2Linked to original sources

arXiv2013

The Gaia-ESO Survey: Reevaluation of the parameters of the open cluster Trumpler 20 using photometry and spectroscopy

Trumpler 20 is an old open cluster (OC) located toward the Galactic centre, at about 3 kpc from the Sun and $\sim$7 kpc from the Galactic centre. Its position makes this cluster particularly interesting in the framework of the chemical properties of the Galactic disc because very few old OCs reside in the inner part of the disc. For this reason it has been selected as a cluster target of the Gaia-ESO Survey, and spectra of many stars in the main sequence and red clump phases are now available. Moreover, although it has been studied by several authors in the past, no consensus on the evolutionary status of Tr 20 has been reached. The heavy contamination of field stars (the line of sight of Tr 20 crosses the Carina spiral arm) complicates a correct interpretation. Another interesting aspect of the cluster is that it shows a broadened main-sequence turn-off and a prominent and extended red-clump, characteristics that are not easily explained by classical evolutionary models. Exploiting both spectroscopic information from the Gaia-ESO Survey (and the ESO archive) and literature photometry, we obtain a detailed and accurate analysis of the properties of the cluster. We make use of the first accurate metallicity measurement ever obtained from several spectra of red clump stars, and of cluster membership determination using radial velocities. According to the evolutionary models adopted, we find that Tr 20 has an age in the range 1.35-1.66 Gyr, an average reddening $E(B-V)$ in the range 0.31-0.35 mag, and a distance modulus $(m-M)_0$ between 12.64 and 12.72 mag. The spectroscopic metallicity is [Fe/H]=+0.17 dex. We discuss the structural properties of the object and constrain possible hypotheses for its broadened upper main sequence by estimating the effect of differential reddening and its extended red clump.

astro-ph.SR↗

arXiv2013

The Origin and Chemical Evolution of the Exotic Globular Cluster NGC3201

NGC3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extraGalactic origin. Our aims are to study NGC3201 in the context of multiple populations (MPs), hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. We present a detailed chemical abundance analysis of eight red giant branch (RGB) stars using high resolution spectroscopy. We measured 29 elements and found [Fe/H]=-1.53+/-0.01, we cannot rule out a metallicity spread of ~0.12 dex, and an alpha-enhancement typical of halo GCs. However significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC3201 appears likely to have had an extraGalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.

astro-ph.GA↗

arXiv2008

Optimal quantum state reconstruction for cold trapped ions

We study the physical implementation of an optimal tomographic reconstruction scheme for the case of determining the state of a multi-qubit system, where trapped ions are used for defining qubits. The protocol is based on the use of mutually unbiased measurements and on the physical information described in H. Häffner \emph{et. al} [Nature \textbf{438}, 643-646 (2005)]. We introduce the concept of physical complexity for different types of unbiased measurements and analyze their generation in terms of one and two qubit gates for trapped ions.

quant-ph↗

arXiv1999

Aspects of Type I String Phenomenology

We study different phenomenological aspects of compact, D=4, N=1 Type IIB orientifolds considered as models for unification of the standard model and gravity. We discuss the structure of the compactification, string and unification scales depending on the different possible D-brane configurations. It is emphasized that in the context of Type I models the $M_W/M_{Planck}$ hierarchy problem is substantially alleviated and may be generated by geometrical factors. We obtain the effective low-energy supergravity Lagrangian and derive the form of soft SUSY-breaking terms under the assumption of dilaton/moduli dominance. We also discuss the role of anomalous U(1)'s and of twisted moduli in this class of theories. A novel mechanism based on the role of singularities is suggested to achieve consistency with gauge coupling unification in low string scale models.

hep-ph↗

arXiv1998

Phenomenological viability of string and M-theory scenarios

We analyze the constraints that a correct phenomenology and the absence of dangerous charge and color breaking (CCB) minima or unbounded from below (UFB) directions impose on the parameter space of different superstring and M-theory scenarios. Namely, we analyze in detail the case where supersymmetry (SUSY) breaking is driven by non-vanishing dilaton and/or moduli F-terms in weakly and strongly coupled strings, and the specific case where the mechanism of SUSY breaking is gaugino condensation with or without the participation of non-perturbative contributions to the K{ä}hler potential. The results indicate that, only in some small windows of the parameter space all the previous tests are succesfully passed. We also discuss the impact of non-universality of the soft breaking terms on CCB/UFB bounds.

hep-ph↗

arXiv1998

String Phenomenology

Following Dyson's analogy between the quantum field theory and the 19th-century chemistry-both explain how but not why-one could also establish an analogy between atomic physics and string theory. Atomic physics was needed to answer the question why in chemistry, string theory is trying to answer the question why in the standard model. This attempt is very briefly reviewed in this talk. After discussing the phenomenological aspects of string theory, the study of soft terms is emphasized as a possible connection between theory and experiment. Special attention is paid to the issues of flavor changing neutral currents, loop effects, charge and color breaking minima, and M-theory versus weakly coupled string theory.

hep-ph↗

arXiv1997

Soft supersymmetry-breaking terms from supergravity and superstring models

We review the origin of soft supersymmetry-breaking terms in N=1 supergravity models of particle physics. We first consider general formulae for those terms in general models with a hidden sector breaking supersymmetry at an intermediate energy scale. The results for some simple models are given. We then consider the results obtained in some simple superstring models in which particular assumptions about the origin of supersymmetry breaking are made. These are models in which the seed of supersymmetry breaking is assumed to be originated in the dilaton/moduli sector of the theory.

hep-ph↗

arXiv1996

Orbifold-induced $μ$ term and electroweak symmetry breaking

It is known that a Higgs $μ$ term can be naturally generated through the Kähler potential in orbifold string models in which one of the three compactified complex planes has order two. In this class of models explicit expressions for both the $μ$ parameter and the soft SUSY-breaking parameters can be obtained under the assumption that the goldstino is an arbitrary linear combination of the fermionic partners of the dilaton $S$ and all the moduli $T_i,U_i$. We apply this picture to the MSSM and explore the consistency of the obtained boundary conditions with radiative gauge symmetry breaking. We find that consistency with the measured value of the top-quark mass can only be achieved if the goldstino has a negligible dilatino component and relevant components along the $T_3,U_3$ moduli associated to the order-two complex plane.

hep-ph↗

arXiv1996

Some Implications of Charge and Color Breaking in the MSSM

We examine some physically relevant implications of potentially dangerous charge and color breaking minima for supersymmetric models. First, we analyze the stability of the corresponding constraints with respect to variations of the initial scale for the running of the soft breaking terms, finding that the larger the scale is, the stronger the bounds become. In particular, by taking $M_P$ rather than $M_X$ for the initial scale, which is a more sensible election, we find substantially stronger and very important constraints. Second, we find general bounds on the universal gaugino mass, the universal scalar mass, $m\geq 55$ GeV, and the Higgs bilinear coefficient, $|B|\simlt 3m$. Finally, we study the infrared fixed point solution of the top quark mass. Again, the constraints on the parameter space turn out to be very important, including the analytically derivable bound $\left|M/m\right|\simlt 1$.

hep-ph↗

arXiv1996

Problems for Supersymmetry Breaking by the Dilaton in Strings from Charge and Color Breaking

The general constraints on the parameter space of soft-breaking terms, in order to avoid dangerous charge and color breaking minima, are applied to the four-dimensional string scenario where the dilaton is the source of supersymmetry breaking (dilaton-dominated limit). The results indicate that the whole parameter space is excluded on these grounds after imposing the present experimental data on the top mass. The inclusion of a non-vanishing cosmological constant does not improve essentially the prospects. Possible way-outs to this situation are briefly discussed.

hep-ph↗

arXiv1996

Soft Terms from Strings

We study the structure of the soft SUSY-breaking terms obtained from 4-D Strings under the assumption of dilaton/moduli dominance in the process of SUSY breaking. We first analyze in detail the dilaton-dominated limit because of its finiteness properties and phenomenological predictivity, and second, we consider the new features appearing when several moduli fields contribute to SUSY breaking. In particular, we discuss in detail the case of symmetric Abelian orbifolds. Although some qualitative features indeed change in the multimoduli case with respect to the dilaton dominance one, the most natural mass relations at low-energy, $m_l < m_q \simeq M_g$, are still similar. Only in some very specific limits these relations might be reversed. We also study the presence of tachyons pointing out that their possible existence may be, in some cases, an interesting advantage in order to break extra gauge symmetries. Finally, we compute explicitly the $μ$ and $B$ parameters in the context of the mechanism for generating a ``$μ$-term'' by the Kähler potential, as naturally implemented in orbifolds. It leads to the prediction $|tgβ|=1$ at the String scale, independently of the Goldstino direction. It is worth noticing that in this squeme the dilaton-dominated case, where there is no free parameters, is excluded since it is not consistent with the measured value of the top-quark mass. In this connection, low-energy charge and color breaking minima are also discussed.

hep-ph↗

arXiv1995

Soft Terms from Dilaton/Moduli sectors

We study the structure of the soft SUSY-breaking terms obtained from large classes of 4-D Strings under the assumption of dilaton/moduli dominance in the process of SUSY-breaking. In particular, we first analyze in detail the dilaton-dominated limit because of its finiteness properties and phenomenological predictivity, and second, we consider the new features appearing when several moduli fields contribute to SUSY breaking. Although some qualitative features indeed change in the multimoduli case with respect to the dilaton dominance one, the most natural mass relations at low-energy $m_l < m_q \simeq M_g$ are still similar. We also study the presence of tachyons pointing out that their possible existence may be, in some cases, an interesting advantage in order to break extra gauge symmetries. Finally, we find that the mechanism for generating a ``$μ$-term'' by the Kähler potential, as naturally implemented in orbifolds, leads to the prediction $|tgβ|=1$ at the String scale, independently of the Goldstino direction. In this connection, it is worth noticing that in the dilaton-dominated case we obtain the remarkable result that the whole SUSY spectrum is completely determined with no free parameters.

hep-ph↗

arXiv1995

Strong Constraints on the Parameter Space of the MSSM from Charge and Color Breaking Minima

A complete analysis of all the potentially dangerous directions in the field-space of the minimal supersymmetric standard model is carried out. They are of two types, the ones associated with the existence of charge and color breaking minima in the potential deeper than the realistic minimum and the directions in the field-space along which the potential becomes unbounded from below. The corresponding new constraints on the parameter space are given in an analytic form, representing a set of necessary and sufficient conditions to avoid dangerous directions. They are very strong and, in fact, there are extensive regions in the parameter space that become forbidden. This produces important bounds, not only on the value of $A$, but also on the values of $B$ and $M_{1/2}$. Finally, the crucial issue of the one-loop corrections to the scalar potential has been taken into account in a proper way.

hep-ph↗

arXiv1995

Soft Supersymmetry-breaking terms and the μproblem

The connection between Supergravity and the low-energy world is analyzed. In particular, the soft Supersymmetry-breaking terms arising in Supergravity, the $μ$ problem and various solutions proposed to solve it are reviewed. The soft terms arising in Supergravity theories coming from Superstring theory are also computed and the solutions proposed to solve the $μ$ problem, which are naturally present in Superstrings, are also discussed. The $B$ soft terms associated are given for the different solutions. Finally, the low-energy Supersymmetric-spectra, which are very characteristic, are obtained.

hep-th↗

arXiv1995

Towards a Theory of Soft Terms for the Supersymmetric Standard Model

We perform a systematic analysis of the soft supersymmetry-breaking terms arising from four-dimensional strings. The analysis does not assume any specific supersymmetry-breaking mechanism but provides a means of parametrizing our ignorance in a way consistent with some known properties of four-dimensional strings. We introduce a {\it goldstino angle} parameter $θ$ which says where the source of supersymmetry-breaking resides, either predominantly in the dilaton sector ($sin θ=1$ limit) or in the rest of the chiral fieds, notably the moduli ($sinθ=0$ limit). All formulae for soft parameters take particularly simple forms when written in terms of this angle. The $sinθ=1$ limit is (up to small corrections) universal. As $sinθ$ decreases, the model dependence increases and the resulting soft terms may or may not be universal, depending on the model. General expressions for the soft terms as functions of $θ$ for generic four-dimensional strings are provided. For each {\it given} string model, one trades the four soft parameters ($M,m,A,B$) of the minimal supersymmetric standard model by the two parameters $m_{3/2}$ (gravitino mass) and $sinθ$. The role of complex phases and the associated constraints from limits on the electric dipole moment of the neutron are discussed. It is also emphasized the importance of treating the problem of the cosmological constant in a self-consistent manner.

hep-ph↗

arXiv1992

Dynamical supersymmetry breaking with a large internal dimension

Supersymmetry breaking in string perturbation theory predicts the existence of a new dimension at the TeV scale. The simplest realization of the minimal supersymmetric Standard Model in the context of this mechanism has two important consequences: (i) A natural solution to the $μ$-problem; (ii) The absence of quadratic divergences in the cosmological constant, which leads to a dynamical determination of the supersymmetry breaking and electroweak scale. We present an explicit example in which the whole particle spectrum is given as a function of the top quark mass. A generic prediction of this mechanism is the existence of Kaluza-Klein excitations for gauge bosons and higgses. In particular the first excitation of the photon could be accessible to future accelerators and give a clear signal of the proposed mechanism.

hep-ph↗

arXiv1992

Soft SUSY Breaking Terms in Stringy Scenarios: Computation and Phenomenological Viability

We calculate the soft SUSY breaking terms arising from a large class of string scenarios, namely symmetric orbifold constructions, and study its phenomenological viability. They exhibit a certain lack of universality, unlike the usual assumptions of the minimal supersymmetric standard model. Assuming gaugino condensation in the hidden sector as the source of SUSY breaking, it turns out that squark and slepton masses tend to be much larger than gaugino masses. Furthermore, we show that these soft breaking terms can be perfectly consistent with both experimental and naturalness constraints (the latter comes from the absence of fine tuning in the $SU(2)\times U(1)_Y\rightarrow U(1)_{em}$ breaking process). This is certainly non--trivial and in fact imposes interesting constraints on measurable quantities. More precisely, we find that the gluino mass ($M_3$) and the chargino mass ($M_{χ^{\pm}}$) cannot be much higher than their present experimental lower bounds ($M_3\stackrel{<}{{}_\sim}285\ $GeV ; $M_{χ^\pm}\stackrel{<}{{}_\sim}80\ $GeV), while squark and slepton masses must be much larger ($\stackrel{>}{{}_\sim} 1\ $TeV). This can be considered as an observational signature of this kind of stringy scenarios. Besides, the top mass is constrained to be within a range ($80\ $GeV$\stackrel{<}{{}_\sim}m_t\stackrel{<}{{}_\sim}165\ $GeV)

hep-ph↗

arXiv1992

Fitting the Quark and Lepton Masses in String Theories

The capability of string theories to reproduce at low energy the observed pattern of quark and lepton masses and mixing angles is examined, focusing the attention on orbifold constructions, where the magnitude of Yukawa couplings depends on the values of the deformation parameters which describe the size and shape of the compactified space. A systematic exploration shows that for $Z_3$, $Z_4$, $Z_6$--I and possibly $Z_7$ orbifolds a correct fit of the physical fermion masses is feasible. In this way the experimental masses, which are low--energy quantities, select a particular size and shape of the compactified space, which turns out to be very reasonable (in particular the modulus $T$ defining the former is $T=O(1)$). The rest of the $Z_N$ orbifolds are rather hopeless and should be discarded on the assumption of a minimal $SU(3)\times SU(2)\times U(1)_Y$ scenario. On the other hand, due to stringy selection rules, there is no possibility of fitting the Kobayashi--Maskawa parameters at the renormalizable level, although it is remarked that this job might well be done by non--renormalizable couplings.

hep-th↗