arXiv subjects

C. Munoz

Publications and source records attributed to C. Munoz.

At least 55 records · Page 3Linked to original sources

arXiv2003

Theoretical Predictions for the Direct Detection of Supersymmetric Dark Matter

We compute the neutralino-nucleon cross section in several supersymmetric scenarios, taking into account all kind of experimental and astrophysical constraints. In addition, the constraints that the absence of dangerous charge and colour breaking minima imposes on the parameter space are also considered. This computation is relevant for the theoretical analysis of the direct detection of dark matter in current experiments. We discuss interesting supergravity and superstring scenarios.

hep-ph↗

arXiv2003

Neutralino-Nucleon Cross Section and Charge and Colour Breaking Constraints

We compute the neutralino-nucleon cross section in several supersymmetric scenarios, taking into account all kind of constraints. In particular, the constraints that the absence of dangerous charge and colour breaking minima imposes on the parameter space are studied in detail. In addition, the most recent experimental constraints, such as the lower bound on the Higgs mass, the $b\to sγ$ branching ratio, and the muon $g-2$ are considered. The astrophysical bounds on the dark matter density are also imposed on the theoretical computation of the relic neutralino density, assuming thermal production. This computation is relevant for the theoretical analysis of the direct detection of dark matter in current experiments. We consider first the supergravity scenario with universal soft terms and GUT scale. In this scenario the charge and colour breaking constraints turn out to be quite important, and $\tanβ\lsim 20$ is forbidden. Larger values of $\tanβ$ can also be forbidden, depending on the value of the trilinear parameter $A$. Finally, we study supergravity scenarios with an intermediate scale, and also with non-universal scalar and gaugino masses where the cross section can be very large.

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arXiv2003

Quark and Lepton Masses and Mixing Angles from Superstring Constructions

We show that the observed structure of quark and lepton masses and mixing angles can arise entirely geometrically from superstring constructions, at the renormalizable level. The model we consider is a $Z_3$ orbifold compactification of heterotic string with two Wilson lines, where three families of particles of $SU(3)_c\times SU(2)_L\times U(1)_Y$, including Higgses, are automatically present. In orbifold models, Yukawa couplings can be calculated explicitly, and it is known that they get exponential supression factors depending on the distance between the fixed points to which the fields are attached. We find that in the $Z_3$ case, the quark and charged-lepton mass hierarchies can easily be obtained for reasonable values of the three moduli determining the radii of the compactified space, $T_i\sim 1$. For the neutrinos, due to the smallness of their Dirac masses, the required scale for the see-saw mechanism to give the correct masses is found to be within reach of the electroweak scale. Finally, we find that one of the small number of possibilities for quark and lepton mass matrices yields consistent results for the mixing angles and the weak CP violation phase. Although our scheme relies on the mixing between fields due to Fayet-Iliopoulos breaking, it is considerably more predictive than alternative models of flavour.

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arXiv2002

Extra matter at low energy

Assuming that the Standard Model arises from the $E_8\times E_8$ Heterotic Superstring, we try to solve the discrepancy between the unification scale predicted by this theory ($\approx g_{GUT}\times 5.27\cdot 10^{17}$ GeV) and the value deduced from LEP experiments ($\approx 2\cdot 10^{16}$ GeV). This will allow us to predict the presence at low energies of three generations of supersymmetric Higgses and vector-like colour triplets.

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arXiv2002

Phenomenology of heterotic M-theory with five-branes

We analyze some phenomenological implications of heterotic M-theory with five-branes. Recent results for the effective 4-dimensional action are used to perform a systematic analysis of the parameter space, finding the restrictions that result from requiring the volume of the Calabi-Yau to remain positive. Then the different scales of the theory, namely, the 11-dimensional Planck mass, the compactification scale and the orbifold scale, are evaluated. The expressions for the soft supersymmetry-breaking terms are computed and discussed in detail for the whole parameter space. With this information we study the theoretical predictions for the supersymmetric contribution to the muon anomalous magnetic moment, using the recent experimental result as a constraint on the parameter space. We finally analyze the neutralino as a dark matter candidate in this construction. In particular, the neutralino-nucleon cross-section is computed and compared with the sensitivities explored by present dark matter detectors.

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arXiv2002

Experimental Constraints on the Neutralino-Nucleon Cross Section

In the light of recent experimental results for the direct detection of dark matter, we analyze in the framework of SUGRA the value of the neutralino-nucleon cross section. We study how this value is modified when the usual assumptions of universal soft terms and GUT scale are relaxed. In particular we consider scenarios with non-universal scalar and gaugino masses and scenarios with intermediate unification scale. We also study superstring constructions with D-branes, where a combination of the above two scenarios arises naturally. In the analysis we take into account the most recent experimental constraints, such as the lower bound on the Higgs mass, the $b\to sγ$ branching ratio, and the muon $g-2$.

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arXiv2002

Relic Neutralino Density in Scenarios with Intermediate Unification Scale

We analyse the relic neutralino density in supersymmetric models with an intermediate unification scale. In particular, we present concrete cosmological scenarios where the reheating temperature is as small as $\cal{O}$ $1 - 1000$ MeV). When this temperature is associated to the decay of moduli fields producing neutralinos, we show that the relic abundance increases considerably with respect to the standard thermal production. Thus the neutralino becomes a good dark matter candidate with $0.1\lsim Ωh^2 \lsim 0.3$, even for regions of the parameter space where large neutralino-nucleon cross sections, compatible with current dark matter experiments, are present. This is obtained for intermediate scales $M_I\sim 10^{11}-10^{14}$ GeV, and moduli masses $m_ϕ\sim 100-1000$ GeV. On the other hand, when the above temperature is associated to the decay of an inflaton field, the relic abundance is too small.

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arXiv2001

Large dark matter cross sections from supergravity and superstrings

We study the direct detection of supersymmetric dark matter in the light of recent experimental results. In particular, we show that regions in the parameter space of several scenarios with a neutralino-nucleon cross section of the order of $10^{-6}$ pb, i.e., where current dark matter detectors are sensitive, can be obtained. These are supergravity scenarios with intermediate unification scale, and superstring scenarios with D-branes.

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arXiv2001

A kind of prediction from superstring model building

Assuming that the Standard Model of particle physics arises from the $E_8\times E_8$ Heterotic String Theory, we try to solve the discrepancy between the unification scale predicted by this theory ($\approx g_{GUT}\times 5.27\cdot 10^{17}$ GeV) and the value deduced from LEP experiments ($\approx 2\cdot 10^{16}$ GeV). A crucial ingredient in our solution is the presence at low energies of three generations of supersymmetric Higgses and vector-like colour triplets. As a by-product our analysis gives rise to a strategy which might be useful when constructing realistic models.

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arXiv2001

Determination of the String Scale in D-Brane Scenarios and Dark Matter Implications

We analyze different phenomenological aspects of D-brane constructions. First, we obtain that scenarios with the gauge group and particle content of the supersymmetric standard model lead naturally to intermediate values for the string scale, in order to reproduce the value of gauge couplings deduced from experiments. Second, the soft terms, which turn out to be generically non universal, and Yukawa couplings of these scenarios are studied in detail. Finally, using these soft terms and the string scale as the initial scale for their running, we compute the neutralino-nucleon cross section. In particular we find regions in the parameter space of D-brane scenarios with cross sections in the range of $10^{-6}$--$10^{-5}$ pb, i.e. where current dark matter experiments are sensitive. For instance, this can be obtained for $\tanβ> 5$.

hep-ph↗

arXiv2001

Supersymmetric dark matter and neutralino-nucleon cross section

We review the direct detection of supersymmetric dark matter in the light of recent experimental results. In particular, we show that regions in the parameter space of several supergravity scenarios with a neutralino-nucleon cross section of order of $10^{-6}$ pb, i.e., where current dark matter detectors are sensitive, can be obtained. These are scenarios with large $\tan β$, with non-universal soft supersymmetry-breaking terms, with multi-TeV masses for scalar superpartners known as `focus point' supersymmetry, and finally scenarios with intermediate unification scale which appear naturally in some superstring constructions.

hep-ph↗

arXiv2001

Muon anomalous magnetic moment in supersymmetric scenarios with an intermediate scale and nonuniversality

We analyze the anomalous magnetic moment of the muon (a_μ) in supersymmetric scenarios. First we concentrate on scenarios with universal soft terms. We find that a moderate increase of a_μ can be obtained by lowering the unification scale M_{GUT} to intermediate values 10^{10-12} GeV. However, large values of \tan βare still favored. Then we study the case of non-universal soft terms. For the usual value M_{GUT}~10^{16} GeV, we obtain a_μ in the favored experimental range even for moderate \tan βregions \tanβ~ 5$. Finally, we give an explicit example of these scenarios. In particular, we show that in a D-brane model, where the string scale is naturally of order 10^{10-12} GeV and the soft terms are non universal, a_μ is enhanced with low \tanβ.

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arXiv2000

Initial Scales, Supersymmetric Dark Matter and Variations of Neutralino-Nucleon Cross Sections

The neutralino-nucleon cross section in the context of the MSSM with universal soft supersymmetry-breaking terms is compared with the limits from dark matter detectors. Our analysis is focussed on the stability of the corresponding cross sections with respect to variations of the initial scale for the running of the soft terms, finding that the smaller the scale is, the larger the cross sections become. For example, by taking $10^{10-12}$ GeV rather than $M_{GUT}$, which is a more sensible choice, in particular in the context of some superstring models, we find extensive regions in the parameter space with cross sections in the range of $10^{-6}$--$10^{-5}$ pb, i.e. where current dark matter experiments are sensitive. For instance, this can be obtained for $\tanβ\gsim 3$.

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arXiv1999

Effective Supergravity from Heterotic M-Theory and its Phenomenological Implications

In this talk I summarize several recent results concerning the four-dimensional effective supergravity obtained using a Calabi-Yau compactification of the $E_8\times E_8$ heterotic string from M-theory. A simple macroscopic study is provided expanding the theory in powers of two dimensionless variables. Higher order terms in the Kähler potential are identified and matched with the heterotic string corrections. In the context of this M-theory expansion, I discuss several phenomenological issues: universality of soft scalar masses, relations between the different scales of the theory (eleven-dimensional Planck mass, compactification scale and orbifold scale) in order to obtain unification at $3\times 10^{16}$ GeV or lower values, soft supersymmetry-breaking terms, and finally charge and colour breaking minima. The above analyses are also carried out in the presence of (non-perturbative) five-branes.

hep-th↗

arXiv1999

Phenomenology of Non-Standard Embedding and Five-branes in M-Theory

We study the phenomenology of the strong-coupling limit of $E_8\times E_8$ heterotic string obtained from M-theory, using a Calabi-Yau compactification. After summarizing the standard embedding results, we concentrate on non-standard embedding vacua as well as vacua where non-perturbative objects as five-branes are present. We analyze in detail the different scales of the theory, eleven-dimensional Planck mass, compactification scale, orbifold scale, and how they are related taking into account higher order corrections. To obtain the phenomenologically favored GUT scale is easier than in standard embedding vacua. To lower this scale to intermediate ($\approx 10^{11}$ GeV) or 1 TeV values or to obtain the radius of the orbifold as large as a millimetre is possible. However, we point out that these special limits are unnatural. Finally, we perform a systematic analysis of the soft supersymmetry-breaking terms. We point out that scalar masses larger than gaugino masses can easily be obtained unlike the standard embedding case and the weakly-coupled heterotic string.

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arXiv1997

"Soft" Phenomenology

A review of the soft supersymmetry-breaking parameters and the $μ$ term arising in superstring models is performed paying special attention to their phenomenological implications. In particular, the violation of the scalar mass universality which may lead to dangerous flavor changing neutral current phenomena and the existence of charge and color breaking minima are discussed. Finally, quadratically-divergent loop effects by pure supergravity interactions on soft parameters and the $μ$ term are also reviewed and applied to superstring models. They provide several new sources of the $μ$ term, naturally of order the weak scale, but also may lead to non--universal soft terms.

hep-ph↗

arXiv1996

An analysis of soft terms in Calabi-Yau compactifications

We perform an analysis of the soft supersymmetry-breaking terms arising in Calabi-Yau compactifications. The sigma-model contribution and the instanton correction to the Kähler potential are included in the computation. The existence of off-diagonal moduli and matter metrics gives rise to specific features as the possibility of having scalars heavier than gauginos or the presence of tachyons. Although non-universal soft terms is a natural situation, we point out that there is an interesting limit where universality is achieved. Finally, we compare these results with those of orbifold compactifications. Although they are qualitatively similar some features indeed change. For example, sum rules found in orbifold models which imply that on average the scalars are lighter than gauginos can be violated in Calabi-Yau manifolds.

hep-ph↗

arXiv1996

Some issues in soft SUSY-breaking terms from dilaton/moduli sectors

We study the structure of the soft SUSY-breaking terms obtained from some classes of 4-D strings under the assumption of dilaton/moduli dominance in the process of SUSY-breaking. We generalize previous analysis in several ways and in particular consider the new features appearing when several moduli fields contribute to SUSY breaking (instead of an overall modulus $T$). Some qualitative features indeed change in the multimoduli case.A general discussion for symmetric Abelian orbifolds as well as explicit examples are given. Certain general sum-rules involving soft terms of different particles are shown to apply to large classes of models. Unlike in the overall modulus $T$ case, gauginos may be lighter than scalars even at the tree-level. However, if one insists in getting that pattern of soft terms, these sum rules force some of the scalars to get negative mass$^2$. These tachyonic masses could be a problem for standard model 4-D strings but an advantage in the case of string-GUTs.We also discuss the possible effects of off-diagonal metrics for the matter fields which may give rise to flavour-changing neutral currents. Different sources for the bilinear $B$ soft term are studied. It is found that the Giudice-Masiero mechanism for generating a ``$μ$-term'', as naturally implemented in orbifolds, leads to the prediction $|tgβ|=1$ at the string scale, independently of the Goldstino direction.

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