arXiv subjects

Pran Nath

Publications and source records attributed to Pran Nath.

At least 145 records · Page 8Linked to original sources

arXiv2006

Probing a Very Narrow $Z'$ Boson with CDF and D0 Data

The CDF and D0 data of nearly 475 $\text{pb}^{-1}$ in the dilepton channel is used to probe a recent class of models, Stueckelberg extensions of the Standard Model (StSM), which predict a $Z'$ boson whose mass is of topological origin with a very narrow decay width. A Drell-Yan analysis for dilepton production via this $Z'$ shows that the current data put constraints on the parameter space of the StSM. With a total integrated luminosity of $8 $ $\text{fb}^{-1}$, the very narrow $Z'$ can be discovered up to a mass of about 600 GeV. The StSM $Z'$ will be very distinct since it can occur in the region where a Randall-Sundrum graviton is excluded.

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arXiv2006

The Stueckelberg Z Prime at the LHC: Discovery Potential, Signature Spaces and Model Discrimination

An analysis is given of the capability of the LHC to detect narrow resonances using high luminosities and techniques for discriminating among models are discussed. The analysis is carried out with focus on the $U(1)_X$ Abelian (Higgless) Stueckelberg extension of the Standard Model (StSM) gauge group which naturally leads to a very narrow $Z'$ resonance. Comparison is made to another class of models, i.e., models based on the warped geometry which also lead to a narrow resonance via a massive graviton ($G$). Methods of distinguishing the StSM $Z'$ from the massive graviton at the LHC are analyzed using the dilepton final state in the Drell-Yan process $pp\to Z'\to l^+l^-$ and $pp\to G \to l^+l^-$. It is shown that the signature spaces in the $σ\cdot Br(l^+l^-) $-resonance mass plane for the $Z$ prime and for the massive graviton are distinct. The angular distributions in the dilepton C-M system are also analyzed and it is shown that these distributions lie high above the background and are distinguishable from each other. A remarkable result that emerges from the analysis is the observation that the StSM model with $Z'$ widths even in the MeV and sub-MeV range for $Z'$ masses extending in the TeV region can produce detectable cross section signals in the dilepton channel in the Drell-Yan process with luminosities accessible at the LHC. While the result is derived within the specific StSM class of models, the capability of the LHC to probe models with narrow resonances in this range may hold more generally.

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arXiv2005

Couplings of Vector-Spinor Representation for SO(10) Model Building

Higgs multiplet in the vector-spinor representations of SO(10), i.e., the $144+\bar{144}$ multiplet can break the SO(10) gauge symmetry spontaneously in one step down to the Standard Model gauge group symmetry $SU(3)_C\times SU(2)_L\times U(1)_Y$ and a recent analysis has used such vector-spinors for building a new class of SO(10) grand unification models (hep-ph/0506312) . Here we discuss the techniques for the computation of several classes of vector-spinor couplings using the Basic Theorem on the SO(2N) vertex expansion developed by the authors. The computations include the cubic couplings of the vector-spinors with SO(10) tensors, quartic self-couplings of the vector-spinors, and couplings of the vector-spinors with spinor representations of SO(10). The last set include couplings of vector-spinors with the 16-plets of quarks and lepton and with the 16 and $\bar{16}$ of Higgs. These couplings provide a crucial tool for further development of the SO(10) grand unification using vector-spinor representations. These include study of quark-lepton masses, analysis of dimension five operators including baryon and lepton number violating operators, and study of neutrino masses and mixings. Illustrative examples are given for their computation using a sample of vector-spinor couplings.

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arXiv2005

Aspects of the Stueckelberg Extension

A detailed analysis of a Stueckelberg extension of the electro-weak gauge group with an extra U(1) factor is presented for the Standard Model as well as for the MSSM. The extra gauge boson gets massive through a Stueckelberg type coupling to a pseudo-scalar, instead of a Higgs effect. This new massive neutral gauge boson Z' has vector and axial vector couplings uniquely different from those of conventional extra abelian gauge bosons, such as appear e.g. in GUT models. The extended MSSM furthermore contains two extra neutralinos and one extra neutral CP-even scalar, the latter with a mass larger than that of the Z'. One interesting scenario that emerges is an LSP that is dominantly composed out of the new neutralinos, leading to a possible new superweak candidate for dark matter. We investigate signatures of the Stueckelberg extension at a linear collider and discuss techniques for the detection of the expected sharp Z' resonance. It turns out that the substantially modified forward-backward asymmetry around the Z' pole provides an important signal. Furthermore, we also elaborate on generalizations of the minimal Stueckelberg extension to an arbitrary number of extra U(1) gauge factors.

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arXiv2005

A Unified Framework for Symmetry Breaking in SO(10)

A new SO(10) unified model is proposed based on a one step breaking of SO(10) to the Standard Model gauge group $SU(3)\times SU(2)\times U(1)_Y$ using a single 144 of Higgs. The symmetry breaking occurs when the SU(5) 24-plet component of 144 develops a vacuum expectation value. Further, it is possible to obtain from the same 144 a light Higgs doublet necessary for electro-weak symmetry breaking using recent ideas of string vacua landscapes and fine tuning. Thus the breaking of SO(10) down to $SU(3)_C\times U(1)_{em}$ can be accomplished with a single Higgs. We analyze this symmetry breaking pattern in the nonsupersymmetric as well as in the supersymmetric SO(10) model.In this scenario masses of the quarks and leptons arise via quartic couplings. We show that the resulting mass pattern is consistent with experimental data, including neutrino oscillations. The model represents an alternative to the currently popular grand unified scenarios.

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arXiv2005

WMAP Dark Matter Constraints and Yukawa Unification in SUGRA models with CP Phases

The compatibility of producing the observed amount of dark matter, as indicated by the WMAP data, through the relic abundance of neutralinos with Yukawa unification and with the measured rate of $b\to s γ$ is analyzed in mSUGRA and extended SUGRA unified models with the inclusion of CP phases. The CP phases affect the analysis in several ways, e.g., through the threshold corrections to the b-quark mass, via their effects on the neutralino relic density and through the SUSY contribution to the BR($b\to s γ$) which is sensitive to the CP phases. We present some specific models with large SUSY phases, which can accommodate the fermion electric dipole moment constraints and give a neutralino relic density in agreement with observations as well as with the b-$τ$ unification constraint. The possibility of achieving WMAP relic density constraints with full Yukawa unification is also explored.

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arXiv2004

How Stueckelberg Extends the Standard Model and the MSSM

Abelian vector bosons can get massive through the Stueckelberg mechanism without spontaneous symmetry breaking via condensation of Higgs scalar fields. This appears very naturally in models derived from string theory and supergravity. The simplest scenarios of this type consist of extensions of the Standard Model (SM) or the minimal supersymmetric standard model (MSSM) by an extra U(1)_X gauge group with Stueckelberg type couplings. For the SM, the physical spectrum is extended by a massive neutral gauge boson Z' only, while the extension of the MSSM contains a CP-even neutral scalar and two extra neutralinos. The new gauge boson Z' can be very light compared to other models with U(1)' extensions. Among the new features of the Stueckelberg extension of the MSSM, the most striking is the possibility of a new lightest supersymmetric particle (LSP) chi_{St}^0 which is mostly composed of Stueckelberg fermions. In this scenario the LSP of the MSSM chi_1^0 is unstable and decays into chi_{St}^0. Such decays alter the signatures of supersymmetry and have impact on searches for supersymmetry in accelerator experiments. Further, with R-parity invariance, chi_{St}^0 is the new candidate for dark matter.

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arXiv2004

Upper limits on sparticle masses from WMAP dark matter constraints with modular invariant soft breaking

An analysis of dark matter within the framework of modular invariant soft breaking is given. In such scenarios inclusion of the radiative electroweak symmetry breaking constraint determines $\tanβ$ which leads to a more constrained analysis. It is shown that for $μ$ positive for this constrained system the WMAP data leads to upper limits on sparticle masses that lie within reach of the LHC with also the possibility that some sparticles may be accessible at RUNII of the Tevatron.

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arXiv2004

Hierarchically Split Supersymmetry with Fayet-Iliopoulos D-terms in String Theory

We show that in string theory or supergravity with supersymmetry breaking through combined F-terms and Fayet-Iliopoulos D-terms, the masses for charged scalars and fermions can be hierarchically split. The mass scale for the gauginos and higgsinos of the MSSM is controlled by the gravitino mass m_{3/2}, as usual, while the scalars get extra contributions from the D-terms of extra abelian U(1) factors, which can make them much heavier. The vanishing of the vacuum energy requires that their masses lie below {m_{3/2} M_{Pl}}^{1/2}, which for m_{3/2}=O(TeV) sets a bound of 10^{10-13} GeV. Thus, scalars with non-vanishing U(1) charges typically become heavy, while others remain light, producing a spectrum of scalars with masses proportional to their charges, and therefore non-universal. This is a modification of the split supersymmetry scenario, but with a light gravitino. We discuss how Fayet-Iliopoulos terms of this size can arise in orientifold string compactifications with D-branes. Furthermore, within the frame work of D-term inflation, the same vacuum energy that generates the heavy scalar masses can be responsible for driving cosmological inflation.

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arXiv2004

Effective Lagrangian for $\bar q\tilde q'_iχ^+_j$, $\bar q\tilde q'_iχ^0_j$ interactions and Fermionic Decays of the Squarks with CP Phases

The one loop corrected effective Lagrangian for the quark-squark-chargino and quark-squark-neutralino interactions is computed. The effective Lagrangian takes into account the loop corrections arising from the exchange of the gluinos, charginos, neutralinos, W, Z, the charged Higgs, and the neutral Higgs. We further analyze the squark decays into charginos and neutralinos and discuss the effect of the loop corrections on them. The analysis takes into account CP phases in the soft parameters. It is found that the loop corrections to the stop decay widths into chargino and neutralinos can be as much as thirty percent or even larger. Further, the stop decay widths show a strong dependence on the CP phases. These results are of relevance in the precision predictions of squark decays in the context of specific models of soft breaking in supergravity and string based models.

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arXiv2004

MSUGRA Dark Matter and the b Quark Mass

We extend the commonly used mSUGRA framework to allow complex soft terms. We show how these phases can induce large changes of the SUSY threshold corrections to the b quark mass and affect the neutralino relic density predictions of the model. We present some specific models with large SUSY phases which can accommodate the fermion electric dipole moment constraints and a neutralino relic density within the WMAP bounds.

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arXiv2004

A Supersymmetric Stueckelberg U(1) Extension of the MSSM

A Stueckelberg extension of the MSSM with only one abelian vector and one chiral superfield as an alternative to an abelian extension with Higgs scalars is presented. The bosonic sector contains a new gauge boson Z' which is a sharp resonance, and a new CP-even scalar, which combines with the MSSM Higgs bosons to produce three neutral CP-even massive states. The neutral fermionic sector has two additional fermions which mix with the four MSSM neutralinos to produce an extended 6x6 neutralino mass matrix. For the case when the LSP is composed mostly of the Stueckelberg fermions, the LSP of the MSSM will be unstable, which leads to exotic decays of sparticles with many leptons in final states. Prospects for supersymmetry searches and for dark matter are discussed.

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arXiv2004

Effective Action and Soft Supersymmetry Breaking for Intersecting D-brane Models

We consider a generic scenario of spontaneous breaking of supersymmetry in the hidden sector within N=1 supersymmetric orientifold compactifications of type II string theories with D-branes that support semi-realistic chiral gauge theories. The soft breaking terms in the visible sector of the models are computed in a standard way without specifying the breaking mechanism, which leads to expressions that generalize those formerly known for heterotic or type I string models. The elements of the effective tree level supergravity action relevant for this, such as the Kahler metric for the matter fields, the superpotential of the visible sector and the gauge kinetic functions, are specified by dimensional reduction and duality arguments. As phenomenological applications we argue that gauge coupling unification can only occur in special regions of the moduli space; we show that flavor changing neutral currents can be suppressed sufficiently for a wide range of parameters, and we briefly address the issues of CP violation, electric dipole moments and dark matter, as well.

hep-th↗

arXiv2004

Modular Invariant Soft Breaking, WMAP, Dark Matter and Sparticle Mass Limits

An analysis of soft breaking under the constraint of modular invariance is given. The role of dilaton and moduli dependent front factors in achieving a modular invariant $V_{soft}$ is emphasized. Further, it is shown that in string models $\tanβ$ is no longer a free parameter but is determined in terms of $α_{string}$ and the other soft parameters by the constraints of modular invariance and radiative electroweak symmetry breaking. The above framework is then used to analyze the neutralino relic density consistent with the WMAP data at self dual points in the Kahler and complex structure moduli. One finds that the combined set of constraints arising from modular invariant soft breaking, radiative electroweak symmetry breaking and WMAP lead to upper limits on sparticle masses for $μ>0$. These limits are investigated for a class of models and found to lie within reach of the Tevatron and of the Large Hadron Collider (LHC). Further, an analysis of the neutralino-proton cross section shows that dark matter in these models can be explored in CDMS (Soudan), GENIUS and ZEPLIN. While the analysis is carried out within the general framework of heterotic strings, the possibility that the results of the analysis may extend to a broader class of string models, such as models based on intersecting D branes, is also discussed.

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arXiv2004

Probing mSUGRA via the Extreme Universe Space Observatory

An analysis is carried out within mSUGRA of the estimated number of events originating from upward moving ultra-high energy neutralinos that could be detected by the Extreme Universe Space Observatory (EUSO). The analysis exploits a recently proposed technique that differentiates ultra-high energy neutralinos from ultra-high energy neutrinos using their different absorption lengths in the Earth's crust. It is shown that for a significant part of the parameter space, where the neutralino is mostly a Bino and with squark mass $\sim 1$ TeV, EUSO could see ultra-high energy neutralino events with essentially no background. In the energy range 10^9 GeV < E < 10^11 GeV, the unprecedented aperture of EUSO makes the telescope sensitive to neutralino fluxes as low as 1.1 \times 10^{-6} (E/GeV)^{-1.3} GeV^{-1} cm^{-2} yr^{-1} sr^{-1}, at the 95% CL. Such a hard spectrum is characteristic of supermassive particles' $N$-body hadronic decay. The case in which the flux of ultra-high energy neutralinos is produced via decay of metastable heavy particles with uniform distribution throughout the universe is analyzed in detail. The normalization of the ratio of the relics' density to their lifetime has been fixed so that the baryon flux produced in the supermassive particle decays contributes to about 1/3 of the events reported by the AGASA Collaboration below 10^{11} GeV, and hence the associated GeV gamma-ray flux is in complete agreement with EGRET data. For this particular case, EUSO will collect between 4 and 5 neutralino events (with 0.3 of background) in ~ 3 yr of running. NASA's planned mission, the Orbiting Wide-angle Light-collectors (OWL), is also briefly discussed in this context.

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arXiv2004

Effective Lagrangian for $χ^+_iχ_j^0H^-$ Interaction in the MSSM and Charged Higgs Decays

We extend previous analyses of the supersymmetric loop correction to the charged Higgs couplings to include the coupling $H^{\pm}χ^{\mp}χ^0$. The analysis completes the previous analyses where similar corrections were computed for $H^+\bar t b$ ($H^-t\bar b$), and for $H^+τ^- \barν_τ$ ($H^- τ^+ ν_τ$) couplings within the minimal supersymmetric standard model. The effective one loop Lagrangian is then applied to the computation of the charged Higgs decays. The sizes of the supersymmetric loop correction on branching ratios of the charged Higgs $H^+(H^-)$ into the decay modes $t\bar b$ ($\bar t b$), $\barτν_τ$ ($τ\bar ν_τ$), and $χ_i^+χ_j^0(χ_i^-χ_j^0)$ (i=1,2; j=1-4) are investigated and the supersymmetric loop correction is found to be significant, i.e., in the range 20-30% in significant regions of the parameter space. The loop correction to the decay mode $χ_1^{\pm}χ_2^0$ is examined in specific detail as this decay mode leads to a trileptonic signal. The effects of CP phases on the branching ratio are also investigated. A brief discussion of the implications of the analysis for collders is given.

hep-ph↗

arXiv2004

Sensitivity of Supersymmetric Dark Matter to the b Quark Mass

An analysis of the sensitivity of supersymmetric dark matter to variations in the b quark mass is given. Specifically we study the effects on the neutralino relic abundance from supersymmetric loop corrections to the mass of the b quark. It is known that these loop corrections can become significant for large $\tanβ$. The analysis is carried out in the framework of mSUGRA and we focus on the region where the relic density constraints are satisfied by resonant annihilation through the s-channel Higgs poles. We extend the analysis to include CP phases taking into account the mixing of the CP-even and CP-odd Higgs boson states which play an important role in determining the relic density. Implications of the analysis for the neutralino relic density consistent with the recent WMAP relic density constraints are discussed.

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arXiv2004

A Stueckelberg Extension of the Standard Model

An extension of the standard model of electro-weak interactions by an extra abelian gauge boson is given, in which the extra gauge boson and the hypercharge gauge boson both couple to an axionic scalar in a form that leads to a Stueckelberg mass term. The theory leads to a massive Z$'$ whose couplings to fermions are uniquely determined and suppressed by small mixing angles. Such a Z$'$ could have low mass and appear in $e^+e^-$ collisions as a sharp resonance. The branching ratios into $f\bar f$ species, and the forward-backward asymmetry are found to have distinctive features. The model also predicts a new unit of electric charge $e'=Q'e$, where $Q'$ is in general irrational, in the coupling of the photon with hidden matter that is neutral under $SU(2)_L\times U(1)_Y$.

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