arXiv subjects

Stefano Profumo

Publications and source records attributed to Stefano Profumo.

At least 253 records · Page 14Linked to original sources

arXiv2006

What mass are the smallest protohalos?

We calculate the kinetic-decoupling temperature for weakly interacting massive particles (WIMPs) in supersymmetric (SUSY) and universal-extra-dimension (UED) models that can account for the cold-dark-matter abundance determined from cosmic microwave background measurements. Depending on the parameters of the particle-physics model, a wide variety of decoupling temperatures is possible, ranging from several MeV to a few GeV. These decoupling temperatures imply a range of masses for the smallest protohalos much larger than previously thought -- ranging from 10^{-6} earth masses to 10^{2} earth masses. We expect the range of protohalos masses derived here to be characteristic of most particle-physics models that can thermally accommodate the required relic abundance of WIMP dark matter, even beyond SUSY and UED.

astro-ph↗

arXiv2006

Dark Matter and the CACTUS Gamma-Ray Excess from Draco

The CACTUS atmospheric Cherenkov telescope collaboration recently reported a gamma-ray excess from the Draco dwarf spheroidal galaxy. Draco features a very low gas content and a large mass-to-light ratio, suggesting as a possible explanation annihilation of weakly interacting massive particles (WIMPs) in the Draco dark-matter halo. We show that with improved angular resolution, future measurements can determine whether the halo is cored or cuspy, as well as its scale radius. We find the relevant WIMP masses and annihilation cross sections and show that supersymmetric models can account for the required gamma-ray flux. The annihilation cross section range is found to be not compatible with a standard thermal relic dark-matter production. We compute for these supersymmetric models the resulting Draco gamma-ray flux in the GLAST energy range and the rates for direct neutralino detection and for the flux of neutrinos from neutralino annihilation in the Sun. We also discuss the possibility that the bulk of the signal detected by CACTUS comes from direct WIMP annihilation to two photons and point out that a decaying-dark-matter scenario for Draco is not compatible with the gamma-ray flux from the Galactic center and in the diffuse gamma-ray background.

astro-ph↗

arXiv2005

Low energy antideuterons: shedding light on dark matter

Low energy antideuterons suffer a very low secondary and tertiary astrophysical background, while they can be abundantly synthesized in dark matter pair annihilations, therefore providing a privileged indirect dark matter detection technique. The recent publication of the first upper limit on the low energy antideuteron flux by the BESS collaboration, a new evaluation of the standard astrophysical background, and remarkable progresses in the development of a dedicated experiment, GAPS, motivate a new and accurate analysis of the antideuteron flux expected in particle dark matter models. To this extent, we consider here supersymmetric, universal extra-dimensions (UED) Kaluza-Klein and warped extra-dimensional dark matter models, and assess both the prospects for antideuteron detection as well as the various related sources of uncertainties. The GAPS experiment, even in a preliminary balloon-borne setup, will explore many supersymmetric configurations, and, eventually, in its final space-borne configuration, will be sensitive to primary antideuterons over the whole cosmologically allowed UED parameter space, providing a search technique which is highly complementary with other direct and indirect dark matter detection experiments.

astro-ph↗

arXiv2005

Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter

In supersymmetric models with non-universal gaugino masses, it is possible to have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the gaugino eigenstates experience little mixing so that the lightest SUSY particle remains either pure bino or pure wino. The neutralino relic density can only be brought into accord with the WMAP measured value when bino-wino co-annihilation (BWCA) acts to enhance the dark matter annihilation rate. We map out parameter space regions and mass spectra which are characteristic of the BWCA scenario. Direct and indirect dark matter detection rates are shown to be typically very low. At collider experiments, the BWCA scenario is typified by a small mass gap m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays of \tilde Z_2 are not allowed. However, in this case the second lightest neutralino has an enhanced loop decay branching fraction to photons. While the photonic neutralino decay signature looks difficult to extract at the Fermilab Tevatron, it should lead to distinctive events at the CERN LHC and at a linear e^+e^- collider.

hep-ph↗

arXiv2005

TeV gamma-rays and the largest masses and annihilation cross sections of neutralino dark matter

Motivated by the interpretation of the recent results on the TeV gamma radiation from the Galactic center, including the new 2004 HESS data, as a by-product of dark matter particles annihilations, we address the question of the largest possible neutralino masses and pair annihilation cross sections in supersymmetric models. Extending the parameter space of minimal models, such as the mSUGRA and the mAMSB scenarios, to general soft SUSY breaking Higgs masses gives access to the largest possible pair annihilation rates, corresponding to resonantly annihilating neutralinos with maximal gaugino-higgsino mixing. Adopting a model-independent approach, we provide analytical and numerical upper limits for the neutralino pair annihilation cross section. A possible loophole is given by the occurrence of non-perturbative electro-weak resonances, a case we also consider here. We then show that a thorough inclusion of QCD effects in gluino (co-)annihilations can, in extreme scenarios, make neutralinos with masses in the hundreds of TeV range, well beyond the s-wave unitarity bound, viable dark matter candidates. Finally, we outline the ranges of neutralino masses and cross sections for models thermally producing a WMAP relic abundance, thus providing reference values for ``best-case'' indirect SUSY dark matter detection rates.

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arXiv2005

Model Independent Approach to Focus Point Supersymmetry: from Dark Matter to Collider Searches

The focus point region of supersymmetric models is compelling in that it simultaneously features low fine-tuning, provides a decoupling solution to the SUSY flavor and CP problems, suppresses proton decay rates and can accommodate the WMAP measured cold dark matter (DM) relic density through a mixed bino-higgsino dark matter particle. We present the focus point region in terms of a weak scale parameterization, which allows for a relatively model independent compilation of phenomenological constraints and prospects. We present direct and indirect neutralino dark matter detection rates for two different halo density profiles, and show that prospects for direct DM detection and indirect detection via neutrino telescopes such as IceCube and anti-deuteron searches by GAPS are especially promising. We also present LHC reach prospects via gluino and squark cascade decay searches, and also via clean trilepton signatures arising from chargino-neutralino production. Both methods provide a reach out to m_{\tg}\sim 1.7 TeV. At a TeV-scale linear e^+e^- collider (LC), the maximal reach is attained in the \tz_1\tz_2 or \tz_1\tz_3 channels. In the DM allowed region of parameter space, a \sqrt{s}=0.5 TeV LC has a reach which is comparable to that of the LHC. However, the reach of a 1 TeV LC extends out to m_{\tg}\sim 3.5 TeV.

hep-ph↗

arXiv2005

Direct, Indirect and Collider Detection of Neutralino Dark Matter In SUSY Models with Non-universal Higgs Masses

In supersymmetric models with gravity-mediated SUSY breaking, universality of soft SUSY breaking sfermion masses m_0 is motivated by the need to suppress unwanted flavor changing processes. The same motivation, however, does not apply to soft breaking Higgs masses, which may in general have independent masses from matter scalars at the GUT scale. We explore phenomenological implications of both the one-parameter and two-parameter non-universal Higgs mass models (NUHM1 and NUHM2), and examine the parameter ranges compatible with Omega_CDM h^2, BF(b --> s,gamma) and (g-2)_mu constraints. In contrast to the mSUGRA model, in both NUHM1 and NUHM2 models, the dark matter A-annihilation funnel can be reached at low values of tan(beta), while the higgsino dark matter annihilation regions can be reached for low values of m_0. We show that there may be observable rates for indirect and direct detection of neutralino cold dark matter in phenomenologically aceptable ranges of parameter space. We also examine implications of the NUHM models for the Fermilab Tevatron, the CERN LHC and a Sqrt(s)=0.5-1 TeV e+e- linear collider. Novel possibilities include: very light s-top_R, s-charm_R squark and slepton_L masses as well as light charginos and neutralinos and H, A and H^+/- Higgs bosons.

hep-ph↗

arXiv2005

Mixed Wino Dark Matter: Consequences for Direct, Indirect and Collider Detection

In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass unification, the predicted relic abundance of neutralinos usually exceeds the strict limits imposed by the WMAP collaboration. One way to obtain the correct relic abundance is to abandon gaugino mass universality and allow a mixed wino-bino lightest SUSY particle (LSP). The enhanced annihilation and scattering cross sections of mixed wino dark matter (MWDM) compared to bino dark matter lead to enhanced rates for direct dark matter detection, as well as for indirect detection at neutrino telescopes and for detection of dark matter annihilation products in the galactic halo. For collider experiments, MWDM leads to a reduced but significant mass gap between the lightest neutralinos so that chi_2^0 two-body decay modes are usually closed. This means that dilepton mass edges-- the starting point for cascade decay reconstruction at the CERN LHC-- should be accessible over almost all of parameter space. Measurement of the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross sections as a function of beam polarization at the International Linear Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in the universe.

hep-ph↗

arXiv2005

Neutralino Cold Dark Matter in a One Parameter Extension of the Minimal Supergravity Model

Within the minimal supergravity model (mSUGRA) framework, the expectation for the relic density of neutralinos exceeds the WMAP determination unless neutralinos a) have a significant higgsino component, b) have a mass close to half that of a heavy Higgs boson, or c)can efficiently co-annihilate with a charged or colored particle. Within a 1-parameter extension of the mSUGRA model which includes non-universal Higgs masses, we show that agreement with the WMAP data can be obtained over a wide range of mSUGRA parameters for scenarios a) and b), so that the phenomenological implications may be much more diverse than in mSUGRA. We show that direct and/or indirect detection of neutralino dark matter should be possible at various current and planned facilities.

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arXiv2005

Neutralino Dark Matter Detection in Split Supersymmetry Scenarios

We study the phenomenology of neutralino dark matter within generic supersymmetric scenarios where the Gaugino and Higgsino masses are much lighter than the scalar soft breaking masses (Split Supersymmetry). We consider a low-energy model-independent approach and show that the guidelines in the definition of this general framework come from cosmology, which forces the lightest neutralino to have a mass smaller than 2.2 TeV. The testability of the framework is addressed by discussing all viable dark matter detection techniques. Current data on cosmic rays antimatter, gamma-rays and on the abundance of primordial 6Li already set significant constraints on the parameter space. Complementarity among future direct detection experiments, indirect searches for antimatter and with neutrino telescopes, and tests of the theory at future accelerators, such as the LHC and a NLC, is highlighted. In particular, we study in detail the regimes of Wino-Higgsino mixing and Bino-Wino transition, which have been most often neglected in the past. We emphasize that our analysis may apply to more general supersymmetric models where scalar exchanges do not provide the dominant contribution to annihilation rates.

hep-ph↗

arXiv2004

A Running Spectral Index in Supersymmetric Dark-Matter Models with Quasi-Stable Charged Particles

We show that charged-particles decaying in the early Universe can induce a scale-dependent or `running' spectral index in the small-scale linear and nonlinear matter power spectrum and discuss examples of this effect in minimal supersymmetric models in which the lightest neutralino is a viable cold-dark-matter candidate. We find configurations in which the neutralino relic density is set by coannihilations with a long-lived stau, and the late decay of staus partially suppresses the linear matter power spectrum. Nonlinear evolution on small scales then causes the modified linear power spectrum to evolve to a nonlinear power spectrum similar (but different in detail) to models parametrized by a constant running $α_{s}=d n_{s}/d{\rm ln} k$ by redshifts of 2 to 4. Thus, Lyman-$α$ forest observations, which probe the matter power spectrum at these redshifts, might not discriminate between the two effects. However, a measurement of the angular power spectrum of primordial 21-cm radiation from redshift $z \approx 30$--$200$ might distinguish between this charged-decay model and a primordial running spectral index. The direct production of a long-lived charged particle at future colliders is a dramatic prediction of this model.

astro-ph↗

arXiv2004

The Role of Antimatter Searches in the Hunt for Supersymmetric Dark Matter

We analyze the antimatter yield of supersymmetric (SUSY) models with large neutralino annihilation cross sections. We introduce three benchmark scenarios, respectively featuring bino, wino and higgsino-like lightest neutralinos, and we study in detail the resulting antimatter spectral features. We carry out a systematic and transparent comparison between current and future prospects for direct detection, neutrino telescopes and antimatter searches. We demonstrate that often, in the models we consider, antimatter searches are the only detection channel which already constrains the SUSY parameter space. Particularly large antiprotons fluxes are expected for wino-like lightest neutralinos, while significant antideuteron fluxes result from resonantly annihilating binos. We introduce a simple and general recipe which allows to assess the visibility of a given SUSY model at future antimatter search facilities. We provide evidence that upcoming space-based experiments, like PAMELA or AMS, are going to be, in many cases, the unique open road towards dark matter discovery.

hep-ph↗

arXiv2004

A Statistical Analysis of Supersymmetric Dark Matter in the MSSM after WMAP

We study supersymmetric dark matter in the general flavor diagonal MSSM by means of an extensive random scan of its parameter space. We find that, in contrast with the standard mSUGRA lore, the large majority of viable models features either a higgsino or a wino-like lightest neutralino, and yields a relic abundance well below the WMAP bound. Among the models with neutralino relic density within the WMAP range, higgsino-like neutralinos are still dominant, though a sizeable fraction of binos is also present. In this latter case, relic density suppression mechanisms are shown to be essential in order to obtain the correct neutralino abundance. We then carry out a statistical analysis and a general discussion of neutralino dark matter direct detection and of indirect neutralino detection at neutrino telescopes and at antimatter search experiments. We point out that current data exclude only a marginal portion of the viable parameter space, and that models whose thermal relic abundance lies in the WMAP range will be significantly probed only at future direct detection experiments. Finally, we emphasize the importance of relic density enhancement mechanisms for indirect detection perspectives, in particular at future antimatter search experiments.

hep-ph↗

arXiv2004

Neutralino Relic Density Enhancement in Non-Standard Cosmologies

The thermal relic abundance of species critically depends on the assumed underlying cosmological model. In the case of neutralinos, freeze-out takes place long before Big Bang Nucleosynthesis, which provides the strongest constraint on the evolution of the Hubble parameter in the Early Universe. We show that non-standard cosmologies, such as models featuring a quintessential scalar field or primordial anisotropies, can lead to large enhancements in the neutralino relic abundance, up to six orders of magnitudes. Within these scenarios, supersymmetric models with large neutralino annihilation cross sections may account for the whole inferred amount of cold dark matter, yielding on the other hand large indirect detection rates.

astro-ph↗

arXiv2003

Non-Universal Gaugino Masses and the Fate of mu -> e gamma

We study charged lepton flavor violating processes in the context of supersymmetric models with non-universal gaugino masses. We consider the generic case of free gaugino masses, as well as specific models based on gaugino mediation and SU(5) GUTs. Under the assumption that the main source of lepton flavor violation resides in the off-diagonal elements of the left handed slepton mass matrix, we show that BR(mu->e gamma) strongly depends on gaugino non-universality. When M_1 and M_2 have opposite signs, cancellations occurring between the neutralino and the chargino contributions can suppress, even completely, the branching ratio of charged lepton flavor violating decays. Moreover, we find that for M_3> M_2,M_1, BR(mu->e gamma) is an increasing function of M_3.

hep-ph↗

arXiv2003

SUSY Dark Matter and Quintessence

We investigate the enhancement of neutralino relic density in the context of a realistic cosmological scenario with Quintessence. The accurate relic density computation we perform allows us to be sensitive to both cases with shifts in the abundance at the percent level, and to enhancements as large as 10^6. We thoroughly analyze the dependence on the supersymmetric spectrum and on the mass and composition of the lightest neutralino. We point out that supersymmetric models yielding a wino or higgsino-like lightest neutralino become cosmologically appealing in the presence of Quintessence.

hep-ph↗

arXiv2003

Neutralino relic density in supersymmetric GUTs with no-scale boundary conditions above the unification scale

We investigate SU(5) and SO(10) GUTs with vanishing scalar masses and trilinear scalar couplings at a scale higher than the unification scale. The parameter space of the models, further constrained by b-τYukawa coupling unification, consists of a common gaugino mass and of \tanβ. We analyze the low energy phenomenology, finding that A-pole annihilations of neutralinos and/or coannihilations with the lightest stau drive the relic density within the cosmologically preferred range in a significant region of the allowed parameter space. Implications for neutralino direct detection and for CERN LHC experiments are also discussed.

hep-ph↗

arXiv2003

Neutralino Dark Matter, b-tau Yukawa Unification and Non-Universal Sfermion Masses

We study the implications of minimal non-Universal Boundary Conditions in the sfermion Soft SUSY Breaking (SSB) masses of mSUGRA. We impose asymptotic b-tau Yukawa coupling Unification and we resort to a parameterization of the deviation from Universality in the SSB motivated by the multiplet structure of SU(5) GUT. A set of cosmo-phenomenological constraints, including the recent results from WMAP, determines the allowed parameter space of the models under consideration. We highlight a new coannihilation corridor where neutralino-sbottom and neutralino-tau sneutrino-stau coannihilations significantly contribute to the reduction of the neutralino relic density.

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