arXiv subjects

J. D. Vergados

Publications and source records attributed to J. D. Vergados.

At least 91 records · Page 5Linked to original sources

arXiv2004

Exploring Novel Signatures for Direct Neutralino Searches

Since the expected rates for neutralino-nucleus scattering are expected to be small, one should exploit all the characteristic signatures of this reaction. Such are: (i) In the standard recoil measurements the modulation of the event rate due to the Earth's motion. (ii) In directional recoil experiments the correlation of the event rate with the sun's motion. One now has both modulation, which is much larger and depends not only on time, but on the direction of observation as well, and a large forward-backward asymmetry. (iii) In non recoil experiments gamma rays following the decay of excited states populated during the Nucleus-LSP collision. Branching ratios of about 6 percent are possible %and (ii) Direct detection of ionization electrons %with branching ratio with respect to the standard recoil of about 10 per cent. (iv) novel experiments in which one observes the electrons produced during the collision of the LSP with the nucleus. Branching ratios of about 10 per cent are possible.

astro-ph↗

arXiv2004

Dark Matter in the Cosmos - Its Direct Detection and the Role Of Nuclear Physics

Exotic dark matter together with dark energy or cosmological constant seem to dominate in the Universe. An even higher density of such matter seems to be gravitationally trapped in our Galaxy. The nature of dark matter can be unveiled only, if it is detected in the laboratory. Thus the accomplishment of this task is central to physics and cosmology. Current fashionable supersymmetric models provide a natural dark matter candidate, which is the lightest supersymmetric particle (LSP). Since the LSP is much heavier than the proton, while its average energy is in the keV region, the most likely possibility for its direct detection is via its elastic scattering with a nuclear target. In order to evaluate the event rate one needs the nuclear structure (form factor and/or spin response function) for the special nuclear targets of experimental interest. Since the expected rates for neutralino-nucleus scattering are expected to be small, one should exploit all the characteristic signatures of this reaction. Such are: (i) In the standard recoil measurements the modulation of the event rate due to the Earth's motion. (ii) In directional recoil experiments the correlation of the event rate with the sun's motion. One now has both modulation, which is much larger and depends not only on time, but on the direction of observation as well, and a large forward-backward asymmetry. (iii) In non recoil experiments gamma rays following the decay of excited states populated during the Nucleus-LSP collision. Branching ratios of about 6 percent are possible. (iv) novel experiments in which one observes the electrons prodused during the collisionof the LSP with the nucleus. Branching ratios of about 10 per cent are possible.

nucl-th↗

arXiv2004

Some Issues Related to the Direct Detection of SUSY Dark Matter Detection

hep-ph↗

arXiv2004

Direct detection of supersymmetric dark matter- Theoretical rates for transitions to excited states

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). Thus the direct dark matter detection is central to particle physics and cosmology. Most of the research on this issue has hitherto focused on the detection of the recoiling nucleus. In this paper we study transitions to the excited states, focusing on the first excited state at 50 keV of Iodine A=127. We find that the transition rate to this excited state is about 10 percent of the transition to the ground state. So, in principle, the extra signature of the gammai ray following its de-excitation can be exploited experimentally.

hep-ph↗

arXiv2004

Neutrinoless Double Beta Decay in Theories Beyond the Standard Model

Neutrinoless double beta decay pops up almost in any extension of the standard model. It is perhaps the only process, which can unambiguously determine whether the massive neutrinos are Majorana or Dirac type particles. In addition from the lifetime of this decay, combined with sufficient knowledge of the relevant nuclear matrix elements, one can set a constraint involving the neutrino masses. Furthemore, if one incorporates the recent results of the neutrino oscillation experiments, one can determine or set a stringent limit on the neutrino mass scale. In addition one may obtain usefull information regarding the presence of right handed currents and the right handed neutrino mass scale. One can also constrain the parameters of supersymmetry and, in particular, set limits in of R-parity violating couplings as well as get information about extra dimensions.

hep-ph↗

arXiv2004

Direct SUSY dark matter detection-Theoretical rates due to the spin

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Thus the direct dark matter detection, consisting of detecting the recoiling nucleus, is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). The relevant cross sections arise out of two mechanisms: i) The coherent mode, due to the scalar interaction and ii) The spin contribution arising from the axial current. In this paper we will focus on the spin contribution, which is expected to dominate for light targets. For both modes it is possible to obtain detectable rates, but in most models the expected rates are much lower than the present experimental goals. So one should exploit two characteristic signatures of the reaction, namely the modulation effect and, in directional experiments, the correlation of the event rates with the sun's motion. In standard non directional experiments the modulation is small, less than two per cent. In the case of the directional event rates we like to suggest that the experiments exploit two features, of the process, which are essentially independent of the SUSY model employed, namely: 1) The forward-backward asymmetry, with respect to the sun's direction of motion, is very large and 2) The modulation is much larger, especially if the observation is made in a plane perpendicular to the sun's velocity. In this case the difference between maximum and minimum can be larger than 40 per cent and the phase of the Earth at the maximum is direction dependent.

hep-ph↗

arXiv2004

Searching for Dark Matter-Can it be directly detected?

In this paper we review the theoretical issues involved in the direct detection of supersymmetric (SUSY) dark matter. After a brief discussion of the allowed SYSY parameter space we focus on the determination of the traditional neutralino detection rates, in experiments which measure the energy of the recoiling nucleus, such as the coherent and spin induced rates and the dependence of the rate on the motion of the Earth (modulation effect). Then we examine the novel features appearing in directional experiments, which detect the recoiling nucleus in a given direction. Next we estimate the branching ratios for transitions to accessible excited nuclear levels. Finally we comment on the event rates leading to the atom ionization and subsequent detection of the outgoing electrons.

astro-ph↗

arXiv2004

Some issues related to the direct detection of dark matter

We briefly review some theoretical issues involved in the direct detection of supersymmetric (SUSY) dark matter. After a brief discussion of the allowed SYSY parameter space we focus on the determination of the traditional neutralino detection rates, in experiments which measure the energy of the recoiling nucleus, such as the coherent and spin induced rates and the dependence of the rate on the motion of the Earth (modulation effect). Then we examine the novel features appearing in directional experiments, which detect the recoiling nucleus in a given direction. Next we estimate the branching ratios for transitions to accessible excited nuclear levels. Finally we estimate the event rates leading to the atom ionization and subsequent detection of the outgoing electrons.

hep-ph↗

arXiv2003

Neutrinos in a spherical box

In the present paper we study some neutrino properties as they may appear in the low energy neutrinos emitted in triton decay with maximum neutrino energy of 18.6 keV. The technical challenges to this end can be achieved by building a very large TPC capable of detecting low energy recoils, down to a a few tenths of a keV, within the required low background constraints. More specifically We propose the development of a spherical gaseous TPC of about 10-m in radius and a 200 Mcurie triton source in the center of curvature. One can list a number of exciting studies, concerning fundamental physics issues, that could be made using a large volume TPC and low energy antineutrinos: 1) The oscillation length involving the small angle of the neutrino mixing matrix, directly measured in this disappearance experiment, is fully contained inside the detector. Measuring the counting rate of neutrino-electron elastic scattering as a function of the distance of the source will give a precise and unambiguous measurement of the oscillation parameters free of systematic errors. In fact first estimates show that even with a year's data taking a sensitivity of a few percent for the measurement of the above angle will be achieved. 2) The low energy detection threshold offers a unique sensitivity for the neutrino magnetic moment which is about two orders of magnitude beyond the current experimental limit. 3) Scattering at such low neutrino energies has never been studied and any departure from the expected behavior may be an indication of new physics beyond the standard model. In this work we mainly focus on the various theoretical issues involved including a precise determination of the Weinberg angle at very low momentum transfer.

hep-ph↗

arXiv2003

Neutrino Properties Studied with a Triton Source Using Large TPC Detectors

The purpose of the present paper is to study the neutrino properties as they may appear in the low energy neutrinos emitted in triton decay, with maximum neutrino energy of 18.6 KeV. The technical challenges to this end can be summarized as building a very large TPC capable of detecting low energy recoils, down to a few 100 eV, within the required low background constraints. More specifically We propose the development of a spherical gaseous TPC of about 10-m in radius and a 200 Mcurie triton source in the center of curvature. One can list a number of exciting studies, concerning fundamental physics issues, that could be made using a large volume TPC and low energy antineutrinos:1) The oscillation length involving the small mixing angle in the electronic neutrino disappearancei experiment is comparable to the length of the detector. Measuring the counting rate of neutrino-electron elastic scattering will give a precise measurement of the oscillation parameters free of systematic errors. First estimations show that a sensitivity of a few percent for the measurement of the above angle. 2) The low energy detection threshold offers a unique sensitivity for the neutrino magnetic moment which is about two orders of magnitude beyond the current experimental limit. 3) Scattering at such low neutrino energies has never been studied and any departure from the expected behavior may be an indication of new physics beyond the standard model. We present results of theoretical calculation and studies of possible measurements.

hep-ex↗

arXiv2003

Theoretical Directional and Modulated Rates for Direct SUSY Dark Matter Detection

Exotic dark matter together with the vacuum energy (cosmological constant) seem to dominate in the flat Universe. Thus direct dark matter detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). It is possible to obtain detectable rates, but realystically they are expected to be much lower than the present experimental goals. So one should exploit two characteristic signatures of the reaction, namely the modulation effect and the correlation with the sun's motion in directional experiments. In standard non directional experiments the modulation is small, less than two per cent. In the case of the directional experiments, the main subject of this paper, we find two novel features, which are essentially independent of the SUSY model employed, namely: 1) The forward-backward asymmetry, with respect to the sun's direction of motion, is very large and 2) The modulation observed in a plane perpendicular to the sun's motion can be higher than 20 per cent and is direction dependent.

hep-ph↗

arXiv2003

New Velocity Distribution in the Context of the Eddington Theory

Exotic dark matter together with the vacuum energy (associated with the cosmological constant) seem to dominate the Universe. Thus its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and velocity distribution of the LSP. The detection rate is proportional to this density in our vicinity. Furthermore, since this rate is expected to be very low, one should explore the two characteristic signatures of the process, namely the modulation effect, i.e. the dependence of the event rate on the Earth's motion and the correlation of the directional rate with the motion of the sun. Both of these crucially depend on the LSP velocity distribution. In the present paper we study simultaneously density profiles and velocity distributions based on the Eddington theory.

astro-ph↗

arXiv2002

Neutrinoless double beta decay from a modern perspective

Neutrinoless double beta decay is a very important process both from the particle and nuclear physics point of view. From the elementary particle point of view it pops up in almost every model. giving rise, among others, to the following mechanisms: a) The traditional contributions like the light neutrino mass mechanism . b) The exotic R-parity violating supersymmetric (SUSY) contributions. Similar considerations apply to its sister lepton and muon number violating muon to positron conversion. The observation of neutrinoless double beta decay will signal that the neutrinos are massive Majorana particles. For nuclear physics it is challenging, because: 1) The nuclei, which can undergo double beta decay, have complicated structure. 2) The energetically allowed transitions are suppressed. 3) One must cope with the short distance behavior of the transition operators. Thus novel effects (decay of pions in flight between nucleons etc) have to be considered. 4) One has to take into account possible momentum dependent terms of the nucleon current. For light neutrinos such modifications of the nucleon current reduce the nuclear matrix elements by about 25 per cent. In the case of heavy neutrino the effect is much larger and model dependent. With the above effects the nuclear matrix elements for all interesting nuclei A = 76, 82, 96, 100, 116, 128, 130, 136 and 150 are discussed. Some have been obtained in the shell model but most in QRPA. Thus we have extracted new limits on the various lepton violating parameters. We find an average neutrino mass of about 0.5eV and, for reasonable choices of the parameters of SUSY models, we get a stringent limit on the R-parity violating parameter less than 0.00068.

hep-ph↗

arXiv2002

Theoretical Directional and Modulated Rates for Direct SUSY Dark Matter Detection

Exotic dark matter together with the vacuum energy (cosmological constant) seem to dominate in the flat Universe. Thus direct dark matter detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). Furthermore from the knowledge of the density and velocity distribution of the LSP, the quark substructure of the nucleon and the nuclear structure (form factor and/or spin response function), one is able to evaluate the event rate for LSP-nucleus elastic scattering. The thus obtained event rates are, however, very low. So it is imperative to exploit the two signatures of the reaction, namely the modulation effect, i.e. the dependence of the event rate on the Earth's motion, and the directional asymmetry, i.e. the dependence of the rate on the the relative angle between the direction of the recoiling nucleus and the sun's velocity. These two signatures are studied in this paper employing various velocity distributions and a supersymmetric model with universal boundary conditions at large tan(beta).

hep-ph↗

arXiv2002

The exotic double-charge exchange muon positron conversion in nuclei

The formalism for the neutrinoless muon positron conversion is investigated in detail and the relevant nuclear matrix elements for light intermediate neutrinos in the case of the experimentally interesting A=27 system are calculated. The nucleus is going to be used as a stopping target in the MECO experiment at Brookhaven, one of the most sensitive probes expected to reach a sensitivity in the branching ratio within the next few years, which will be an improvement of three orders of magnitude. The relevant transition operators are constructed utilizing a variety of mechanisms present in current gauge theories, with emphasis on the intermediate neutrinos, both light and heavy, and heavy SUSY particles. The nuclear wave functions, both for the initial state and all excited final states are obtained in the framework of 1s-0d shell model employing the well-known and tested Wildenthal realistic interaction. In the case of the light intermediate neutrinos the transition rates to all excited final states up to 25 MeV in energy are calculated. We find that the imaginary part of the amplitude is dominant. The total rate is calculated by summing over all these partial transition strengths. We also find that the rate due to the real part of the amplitude is much smaller than the corresponding quantity found previously by the closure approximation.

nucl-th↗

arXiv2002

Theoretical Rates for Direct Detection of SUSY Dark Matter

Exotic dark matter together with the vacuum energy (associated with the cosmological constant) seem to dominate in the Universe. Thus its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). Furtheremore from the knowlegde of the density and velocity distribution of the LSP, the quark substructure of the nucleon and the nuclear structure (form factor and/or spin response function), one is able to evaluate the event rate for LSP-nucleus elastic scattering. The thus obtained event rates are, however, very low. So it is imperative to exploit the modulation effect, i.e. the dependence of the event rate on the Earth's motion and the directional signature, i.e. the dependence of the rate on the direction of the recoiling nucleus. In this paper we study such experimental signatures employng a supersymmetric model with universal boundary conditions at large tangent beta.

astro-ph↗

arXiv2002

SUSY Dark Matter in the Universe- Theoretical Direct Detection Rates

Exotic dark matter together with the vacuum energy or cosmological constant seem to dominate in the Universe. An even higher density of such matter seems to be gravitationally trapped in the Galaxy. Thus its direct detection is central to particle physics and cosmology. Current supersymmetric models provide a natural dark matter candidate which is the lightest supersymmetric particle (LSP). Such models combined with fairly well understood physics like the quark substructure of the nucleon and the nuclear structure (form factor and/or spin response function), permit the evaluation of the event rate for LSP-nucleus elastic scattering. The thus obtained event rates are, however, very low or even undetectable. So it is imperative to exploit the modulation effect, i.e. the dependence of the event rate on the earth's annual motion. Also it is useful to consider the directional rate, i.e its dependence on the direction of the recoiling nucleus. In this paper we study such a modulation effect both in non directional and directional experiments. We calculate both the differential and the total rates using both isothermal, symmetric as well as only axially asymmetric, and non isothermal, due to caustic rings, velocity distributions. We find that in the symmetric case the modulation amplitude is small. The same is true for the case of caustic rings. The inclusion of asymmetry, with a realistic enhanced velocity dispersion in the galactocentric direction, yields an enhanced modulation effect, especially in directional experiments.

hep-ph↗

arXiv2001

SUSY Dark Matter Detection, The Directional Rate and the Modulation effect

The detection of the theoretically expected dark matter is central to particle physics and cosmology. Current fashionable supersymmetric models provide a natural dark matter candidate which is the lightest supersymmetric particle (LSP). Such models combined with fairly well understood physics like the quark substructure of the nucleon and the nuclear structure (form factor and/or spin response function), permit the evaluation of the event rate for LSP-nucleus elastic scattering. The thus obtained event rates are, however, very low or even undetectable. So it is imperative to exploit the modulation effect, i.e. the dependence of the event rate on the earth's annual motion. Also it is useful to consider the directional rate, i.e its dependence on the direction of the recoiling nucleus. In this paper we study such a modulation effect both in non directional and directional experiments. We calculate both the differential and the total rates using both isothermal, symmetric as well as only axially asymmetric, and non isothermal, due to caustic rings, velocity distributions. We find that in the symmetric case the modulation amplitude is small. The same is true for the case of caustic rings. The inclusion of asymmetry, with a realistic enhanced velocity dispersion in the galactocentric direction, yields an enhanced modulation effect, especially in directional experiments.

hep-ph↗