Stefano Profumo

Dark matter and collider phenomenology of universal extra dimensions

Abstract We review the phenomenology of models with flat, compactified extra dimensions where all of the Standard Model fields are allowed to propagate in the bulk, known as Universal Extra Dimensions (UED). UED make for an interesting TeV-scale physics scenario, featuring a tower of Kaluza–Klein (KK) states approximately degenerate in mass at the scale set by the inverse size of the compactification radius. KK parity, the four-dimensional remnant of momentum conservation in the extra dimensions, implies two basic consequences: (1) contributions to Standard Model observables arise only at loop level, and KK states can only be pair-produced at colliders, and (2) the lightest KK particle (LKP) is stable, providing a suitable particle dark matter candidate. After a theoretical overview on extra dimensional models, and on UED in particular, we introduce the model particle spectrum and the constraints from precision electroweak tests and current colliders data. We then give a detailed overview of the LKP dark matter phenomenology, including the LKP relic abundance, and direct and indirect searches. We then discuss the physics of UED at colliders, with particular emphasis on the signatures predicted for the Large Hadron Collider and at a future Linear Collider, as well as on the problem of discriminating between UED and other TeV-scale new physics scenarios, particularly supersymmetry. We propose a set of reference benchmark models, representative of different viable UED realizations. Finally, we collect in the Appendix all the relevant UED Feynman rules, the scattering cross sections for annihilation and coannihilation processes in the early universe and the production cross section for strongly interacting KK states at hadron colliders.

On possible interpretations of the high energy electron–positron spectrum measured by the Fermi Large Area Telescope

The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. Here we discuss several interpretations of the Fermi results based either on a single large scale Galactic CRE component or by invoking additional electron–positron primary sources, e.g. nearby pulsars or particle dark matter annihilation. We show that while the reported Fermi-LAT data alone can be interpreted in terms of a single component scenario, when combined with other complementary experimental results, specifically the CRE spectrum measured by H.E.S.S. and especially the positron fraction reported by PAMELA between 1 and 100 GeV, that class of models fails to provide a consistent interpretation. Rather, we find that several combinations of parameters, involving both the pulsar and dark matter scenarios, allow a consistent description of those results. We also briefly discuss the possibility of discriminating between the pulsar and dark matter interpretations by looking for a possible anisotropy in the CRE flux.

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 m0 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 ΩCDMh2, BF(b→sγ) and (g−2)μ constraints. We have demonstrated that 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 β, while the higgsino dark matter annihilation regions can be reached for low values of m0. 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 (s)1/2 = 0.5−1 TeV e+e− linear collider. Novel possibilities include: very light R, R squark and L slepton masses as well as light charginos and neutralinos and H, A and H± Higgs bosons.

Singlet Higgs phenomenology and the electroweak phase transition

We study the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. We determine the conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe. We analyze the constraints on the potential parameters derived from Higgs boson searches at LEP and electroweak precision observables. For models that satisfy these constraints and that produce a strong first order phase transition, we discuss the prospective signatures in future Higgs studies at the Large Hadron Collider and a Linear Collider. We argue that such studies will provide powerful probes of phase transition dynamics in models with an extended scalar sector.

What mass are the smallest protohalos

We calculate the kinetic-decoupling temperature for weakly interacting massive particles (WIMPs) in supersymmetric (SUSY) and extra dimensional 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)M(+ in a circle) to 10(2)M(+ in a circle). 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 extra dimensions.

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 coannihilate with a charged or colored particle. Within a one-parameter extension of the mSUGRA model which includes nonuniversal 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.

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 cases with both shifts in the abundance at the per cent level, and enhancements as large as 106. We thoroughly analyse 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.

Discovery of a 3.5 keV line in the Galactic Centre and a critical look at the origin of the line across astronomical targets

We examine the claimed excess X-ray line emission near 3.5 keV including both a new analysis of XMM-Newtonobservations of the Milky Way center and a reanalysis of the data on M 31 and clusters. In no case do we find conclusive evidence for an excess. In the case of the Galactic center we show that known plasma lines, including in particular K XVIII lines at 3.48 and 3.52 keV, provide a satisfactory fit to the XMM data. We estimate the expected flux of the K XVIII lines and find that the measured line flux falls sq uarely within the predicted range based on the brightness of other well-measured lines in the energy range of interest and on detailed multi-temperature plasma models. We then re-assess the evidence for excess emission from clusters of galaxies, allowing for systematic uncertainty in the expected flux from known plasma lines and additional uncertainty due to potential variation in the abundances of different elements. We find that no conclusive excess line em ission can be advocated when considering systematic uncertainties in Perseus or in othe r clusters. We also re-analyze the XMM data for M 31 and find no statistically significant line emissi on near 3.5 keV to a level greater than one sigma. Finally, we analyze the Tycho supernova remnant, which shows similar plasma features to the sources above, but does not host any significant dark matter. We detect a 3.55 keV line from Tycho, which points to possible systematic effects in the flux determination of weak lines, or to relative elemental abundances vastly different from theoretical expectations.

Effective field theory approach to the Galactic Center gamma-ray excess

We explore the possibility of explaining a gamma-ray excess in the Galactic center, originally pointed out by Hooper, collaborators, and other groups, in an effective field theory framework. We assume that dark matter annihilation is mediated by particles heavy enough to be integrated out, and that such particles couple to all quark families. We calculate the effective coupling required to explain the annihilation signal in the Galactic center, and compare with bounds from direct detection, collider searches, and the requirement that the dark matter particle make up the appropriate fraction of the universal energy budget. We find that only a very small set of operators can explain the gamma-ray excess while being consistent with other constraints. Specifically, for scalar dark matter the viable options are one scalar-type coupling to quarks and one interaction with gluons, while for fermionic (Dirac) dark matter the viable options are two scalar-type dimension-7 operators or a dimension-6 vector-type operator. In all cases, future searches with the Large Hadron Collider should probe the relevant operators’ effective energy scale, while all viable interactions should escape direct detection experiments. 1 ar X iv :1 40 3. 50 27 v1 [ he pph ] 2 0 M ar 2 01 4

Statistical analysis of supersymmetric dark matter in the minimal supersymmetric standard model 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. PACS numbers: 12.60.Jv, 14.80.Ly, 95.35.+d