arXiv subjects

Paolo Gondolo

Publications and source records attributed to Paolo Gondolo.

At least 127 records · Page 7Linked to original sources

arXiv2001

Detectability of a subdominant density component of cold dark matter

Here we examine the detectability of collisionless dark matter candidates that may constitute not all but only a subdominant component of galactic cold dark matter. We show that current axion searches are not suited for a subdominant component, while direct WIMP searches would not be severely affected by the reduced density. In fact, the direct detection rates of neutralinos stay almost constant even if neutralinos constitute 1% of the halo dark matter. Only for lower densities do the rates decrease with density. Even neutralinos accounting for only $10^{-4}$ of the local dark halo density are within proposed future discovery limits. We comment also on indirect WIMP searches.

hep-ph↗

arXiv2001

Binary events and extragalactic planets in pixel microlensing

Pixel microlensing, i.e. gravitational microlensing of unresolved stars, can be used to explore distant stellar systems, and as a bonus may be able to detect extragalactic planets. In these studies, binary-lens events with multiple high-magnification peaks are crucial. Considering only those events which exhibit caustic crossings, we estimate the fraction of binary events in several example pixel microlensing surveys and compare them to the fraction of binary events in a classical survey with resolved stars. We find a considerable enhancement of the relative rate of binary events in pixel microlensing surveys, relative to surveys with resolved sources. We calculate the rate distribution of binary events with respect to the time between caustic crossings. We consider possible surveys of M31 with ground-based telescopes and of M87 with HST and NGST. For the latter, a pixel microlensing survey taking one image a day may observe of order one dozen binary events per month.

astro-ph↗

arXiv2000

DarkSUSY - A numerical package for dark matter calculations in the MSSM

The question of the nature of the dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino. We here describe DarkSUSY, an advanced numerical FORTRAN package for supersymmetric dark matter calculations which we release for public use. With the help of this package, the masses and compositions of various supersymmetric particles can be computed, for given input parameters of the minimal supersymmetric extension of the Standard Model (MSSM). For the lightest neutralino, the relic density is computed, using accurate methods which include the effects of resonances, pair production thresholds and coannihilations. Accelerator bounds are checked to identify viable dark matter candidates. Finally, detection rates are computed for a variety of detection methods, such as direct detection and indirect detection through antiprotons, gamma-rays and positrons from the Galactic halo or neutrinos from the center of the Earth or the Sun.

astro-ph↗

arXiv2000

Measurement of the gluon PDF at small x with neutrino telescopes

We analyze the possibility that neutrino telescopes may provide an experimental determination of the slope lambda of the gluon distribution in the proton at momentum fractions x smaller than the accelerator reach. The method is based on a linear relation between lambda and the spectral index (slope) of the down-going atmospheric muon flux above 100 TeV, for which there is no background. Considering the uncertainties in the charm production cross section and in the cosmic ray composition, we estimate the error on the measurement of lambda through this method, excluding the experimental error of the telescopes, to be ~ +/- 0.2

hep-ph↗

arXiv2000

Neutralino dark matter vs galaxy formation

Neutralino dark matter may be incompatible with current cold dark matter models with cuspy dark halos, because excessive synchrotron radiation may originate from neutralino annihilations close to the black hole at the galactic center.

hep-ph↗

arXiv2000

Either neutralino dark matter or cuspy dark halos

We show that if the neutralino in the minimal supersymmetric standard model is the dark matter in our galaxy, there cannot be a dark matter cusp extending to the galactic center. Conversely, if a dark matter cusp extends to the galactic center, the neutralino cannot be the dark matter in our galaxy. We obtain these results considering the synchrotron emission from neutralino annihilations around the black hole at the galactic center.

hep-ph↗

arXiv2000

Dark Matter at the Galactic Center

Particle dark matter near the galactic center is accreted by the central black hole into a dense spike, strongly enhancing its annihilation rate. Searching for its annihilation products may give us information on the presence or absence of a central cusp in the dark halo profile. We summarize our paper Phys Rev Lett 83, 1719 (1999), and use an updated limit on the neutrino emission from the galactic center.

hep-ph↗

arXiv2000

Effects of CP-Violation in Neutralino Scattering and Annihilation

We summarize our paper hep-ph/9908390, where we find that in some regions of supersymmetric parameter space, CP violating effects that mix the CP-even and CP-odd Higgs bosons can enhance the neutralino annihilation rate by factors of 10^6, and reduce the neutralino scattering rate off nucleons by factors of 10^{-7}.

hep-ph↗

arXiv1999

Searching for extragalactic planets

Are there other planetary systems in our Universe? Indirect evidence has been found for planets orbiting other stars in our galaxy: the gravity of orbiting planets makes the star wobble, and the resulting periodic Doppler shifts have been detected for about a dozen stars. But are there planets in other galaxies, millions of light years away? Here we suggest a method to search for extragalactic planetary systems: gravitational microlensing of unresolved stars. This technique may allow us to discover planets in elliptical galaxies, known to be far older than our own Milky Way, with broad implications for life in the Universe.

astro-ph↗

arXiv1999

CP-Violating Effects in Neutralino Scattering and Annihilation

We show that in some regions of supersymmetric parameter space, CP violating effects that mix the CP-even and CP-odd Higgs bosons can enhance the neutralino annihilation rate, and hence the indirect detection rate of neutralino dark matter, by factors of 10^6. The same CP violating effects can reduce the neutralino scattering rate off nucleons, and hence the direct detection rate of neutralino dark matter, by factors of 10^{-7}. We study the dependence of these effects on the phase of the trilinear coupling A, and find cases in the region being probed by dark matter searches which are experimentally excluded when CP is conserved but are allowed when CP is violated.

hep-ph↗

arXiv1999

Dark matter annihilation at the galactic center

If cold dark matter is present at the galactic center, as in current models of the dark halo, it is accreted by the central black hole into a dense spike. Particle dark matter then annihilates strongly inside the spike, making it a compact source of photons, electrons, positrons, protons, antiprotons, and neutrinos. The spike luminosity depends on the density profile of the inner halo: halos with finite cores have unnoticeable spikes, while halos with inner cusps may have spikes so bright that the absence of a detected neutrino signal from the galactic center already places interesting upper limits on the density slope of the inner halo. Future neutrino telescopes observing the galactic center could probe the inner structure of the dark halo, or indirectly find the nature of dark matter.

astro-ph↗

arXiv1999

Indirect Detection of Dark Matter in km-size Neutrino Telescopes

Neutrino telescopes of kilometer size are currently being planned. They will be two or three orders of magnitude larger than presently operating detectors, but they will have a much higher muon energy threshold. We discuss the trade-off between area and energy threshold for indirect detection of neutralino dark matter captured in the Sun and in the Earth and annihilating into high energy neutrinos. We also study the effect of a higher threshold on the complementarity of different searches for supersymmetric dark matter.

astro-ph↗

arXiv1999

Prompt atmospheric neutrinos and muons: dependence on the gluon distribution function

We compute the next-to-leading order QCD predictions for the vertical flux of atmospheric muons and neutrinos from decays of charmed particles, for different PDF's (MRS-R1, MRS-R2, CTEQ-4M and MRST) and different extrapolations of these at small partonic momentum fraction x. We find that the predicted fluxes vary up to almost two orders of magnitude at the largest energies studied, depending on the chosen extrapolation of the PDF's. We show that the spectral index of the atmospheric leptonic fluxes depends linearly on the slope of the gluon distribution function at very small x. This suggests the possibility of obtaining some bounds on this slope in ``neutrino telescopes'', at values of x not reachable at colliders, provided the spectral index of atmospheric leptonic fluxes could be determined.

hep-ph↗

arXiv1999

Prompt atmospheric neutrinos and muons: NLO vs LO QCD predictions

We compare the leading and next-to-leading order QCD predictions for the flux of atmospheric muons and neutrinos from decays of charmed particles. We find that the full NLO lepton fluxes can be approximated to within 10% by the Born--level fluxes multiplied by an overall factor of 2.2-2.4, which depends slightly on the PDF. This supports the approach in Thunman, Ingelman, Gondolo (1996). We also find that their very low lepton fluxes are due to the mild slope they used for the gluon distribution function at small momentum fractions, and that substantially larger lepton fluxes result when the slope of the gluon distribution function at small momentum fractions is larger.

hep-ph↗

arXiv1998

Optical depth evaluation in pixel microlensing

We propose an estimator of the microlensing optical depth from pixel lensing data that involves only measurable quantities. In comparison to the only previously proposed estimator, it has the advantage of not being limited to events with large magnification at maximum, and it applies equally well to satellite and ground-based observations.

astro-ph↗

arXiv1998

Evidence for "sterile neutrino" dark matter?

I show that it may be possible to explain the present evidence for a gamma-ray emission from the galactic halo as due to halo WIMP annihilations. Not only the intensity and spatial pattern of the halo emission can be matched but also the relic density of the candidate WIMP can be in the cosmologically interesting domain. After a model-independent analysis to learn about the properties of a suitable candidate, I present a working model: a sterile neutrino in a model with an extended Higgs sector. Two examples indicate the existence of an interesting region in the model parameter space where present observational and experimental constraints are satisfied and the gamma-ray emission is reproduced.

hep-ph↗

arXiv1998

The Gamma-Ray Halo from Dark Matter Annihilations

A sophisticated analysis of EGRET data has found evidence for gamma-ray emission from the galactic halo. I entertain the possibility that part of the EGRET signal is due to WIMP annihilations in the halo. I show that a viable candidate with the required properties exists in a model with an extended Higgs sector. The candidate has a mass of 2--4 GeV, a relic density $Ω\sim 0.1$ (for a Hubble constant of 60 km/s/Mpc), and a scattering cross section off nucleons in the range $10^{-5}$--$10^{-1}$ pb. The model satisfies present observational and experimental constraints, and makes strict predictions on the gamma-ray spectrum of the halo emission.

astro-ph↗

arXiv1998

Limits on R-parity violation from cosmic ray antiprotons

We constrain the hadronic R-parity violating couplings in extensions to the minimal supersymmetric standard model. These interactions violate baryon and lepton number, and allow the lightest superpartner (LSP) to decay into standard model particles. The observed flux of cosmic ray antiprotons places a strong bound on the lifetime of the LSP in models where the lifetime is longer than the age of the universe. We exclude 10^-18<lambda''<10^-15 and 2x10^-18<lambda'<2x10^-15 except in the case of a top quark, where we can only exclude 4x10^-19<lambda'<4x10^-16.

hep-ph↗