arXiv subjects

Pran Nath

Publications and source records attributed to Pran Nath.

At least 127 records · Page 7Linked to original sources

arXiv2008

Predicted Signatures at the LHC from U(1) Extensions of the Standard Model

We discuss the $U(1)_X$ extensions of the standard model with focus on the Stueckelberg mechanism for mass growth for the extra $U(1)_X$ gauge boson. The assumption of an axionic connector field which carries dual U(1) quantum numbers, i.e., quantum numbers for the hypercharge $U(1)_Y$ and for the hidden sector gauge group $U(1)_X$, allows a non-trivial mixing between the mass growth for the neutral gauge vector bosons in the $SU(2)_L\times U(1)_Y$ sector and the mass growth for the vector boson by the \st mechanism in the $U(1)_X$ sector. This results in an extra $Z'$ which can be very narrow, but still detectable at the Large Hadron Collider (LHC). The $U(1)_X$ extension of the minimal supersymmetric standard model is also considered and the role of the Fayet-Illiopoulos term in such an extension discussed. The $U(1)_X$ extensions of the SM and of the MSSM lead to new candidates for dark matter.

hep-ph↗

arXiv2008

High Scale Physics Connection to LHC Data

The existing data appears to provide hints of an underlying high scale theory. These arise from the gauge coupling unification, from the smallness of the neutrino masses, and via a non-vanishing muon anomaly. An overview of high scale models is given with a view to possible tests at the Large Hadron Collider. Specifically we discuss here some generic approaches to deciphering their signatures. We also consider an out of the box possibility of a four generation model where the fourth generation is a mirror generation rather than a sequential generation. Such a scenario can lead to some remarkably distinct signatures at the LHC.

hep-ph↗

arXiv2008

An MSSM Extension with a Mirror Fourth Generation, Neutrino Magnetic Moments and LHC Signatures

Recent analyses have shown that a sequential fourth generation can be consistent with precision electroweak data. We consider the possibility that the new generation could be a mirror generation with $V+A$ rather than $V-A$ interactions. Specifically we consider an extension of the minimal supersymmetric standard model with a light mirror generation (mirMSSM) . Implications of this extension are explored. One consequence is an enhancement of the tau neutrino magnetic moment by several orders of magnitude consistent with the current limits on the magnetic moment of the tau. The masses of the mirror generation arise due to electroweak symmetry breaking, and if a mirror generation exists its mass spectrum must lye below a TeV, and thus should be discovered at the LHC. Mirror particles and mirror sparticles produce many characteristic signatures which should be detectable at the LHC. Heavy higgs boson decays into mirror particles and an analysis of the forward-backward asymmetries can distinguish a mirror generation from a sequential fourth generation. The validity of the model can thus be tested at the LHC. A model of the type discussed here could arise from a more unified structure such as grand unification or strings where a mirror generation escapes the survival hypothesis, i.e., a generation and a mirror generation do not tie up to acquire a mass of size $M_{GUT}$ or $M_{string}$ due to a symmetry, and thus remain massless down to the electroweak scale.

hep-ph↗

arXiv2008

Decoding the Mechanism for the Origin of Dark Matter in the Early Universe Using LHC Data

It is shown that LHC data can allow one to decode the mechanism by which dark matter is generated in the early universe in supersymmetric theories. We focus on two of the major mechanisms for such generation of dark matter which are known to be the Stau Coannihilation (Stau-Co) where the neutralino is typically Bino like and annihilation on the Hyperbolic Branch (HB) where the neutralino has a significant Higgsino component. An investigation of how one may discriminate between the Stau-Co region and the HB region using LHC data is given for the mSUGRA model. The analysis utilizes several signatures including multi leptons, hadronic jets, b-tagging, and missing transverse momentum. A study of the SUSY signatures reveals several correlated smoking gun signals allowing a clear discrimination between the Stau-Co and the HB regions where dark matter in the early universe can originate.

hep-ph↗

arXiv2008

Recent Developments in Supersymmetric and Hidden Sector Dark Matter

New results which correlate SUSY dark matter with LHC signals are presented, and a brief review of recent developments in supersymmetric and hidden sector dark matter is given. It is shown that the direct detection of dark matter is very sensitive to the hierarchical SUSY sparticle spectrum and the spectrum is very useful in distinguishing models. It is shown that the prospects of the discovery of neutralino dark matter are very bright on the "Chargino Wall" due to a copious number of model points on the Wall, where the NLSP is the Chargino, and the spin independent neutralino-proton cross section is maintained at high values in the $10^{-44}$cm$^{2}$ range for neutralino masses up to $\sim 850$ GeV . It is also shown that the direct detection of dark matter along with lepton plus jet signatures and missing energy provide dual, and often complementary, probes of supersymmetry. Finally, we discuss an out of the box possibility for dark matter, which includes dark matter from the hidden sector, which could either consist of extra weakly interacting dark matter (a Stino XWIMP), or milli-charged dark matter arising from the Stueckelberg extensions of the MSSM or the SM.

hep-ph↗

arXiv2008

Sparticles at the LHC

Sparticle mass hierarchies will play an important role in the type of signatures that will be visible at the Large Hadron Collider. We analyze these hierarchies for the four lightest sparticles for a general class of supergravity unified models including nonuniversalities in the soft breaking sector. It is shown that out of nearly $10^4$ possibilities of sparticle mass hierarchies, only a small number survives the rigorous constraints of radiative electroweak symmetry breaking, relic density and other experimental constraints. The signature space of these mass patterns at the Large Hadron Collider is investigated using a large set of final states including multi-leptonic states, hadronically decaying $τ$s, tagged $b$ jets and other hadronic jets. In all, we analyze more than 40 such lepton plus jet and missing energy signatures along with several kinematical signatures such as missing transverse momentum, effective mass, and invariant mass distributions of final state observables. It is shown that a composite analysis can produce significant discrimination among sparticle mass patterns allowing for a possible identification of the source of soft breaking. While the analysis given is for supergravity models, the techniques based on mass pattern analysis are applicable to wide class of models including string and brane models.

hep-ph↗

arXiv2008

Light Higgses at the Tevatron and at the LHC and Observable Dark Matter in SUGRA and D Branes

Sparticle landscapes in mSUGRA, in SUGRA models with nonuniversalities (NUSUGRA), and in D brane models are analyzed. The analysis exhibits the existence of Higgs Mass Patterns (HPs) (for $μ>0$) where the CP odd Higgs could be the next heavier particle beyond the LSP and sometimes even lighter than the LSP. It is shown that the Higgs production cross sections from the HPs are typically the largest enhancing the prospects for their detection at the LHC. Indeed it is seen that the recent Higgs production limits from CDF/DØ are beginning to put constraints on the HPs. It is also seen that the $B_s\to μ^+μ^-$ limits constrain the HPs more stringently. Predictions of the Higgs production cross sections for these patterns at the LHC are made. We compute the neutralino-proton cross sections $σ(χp)$ for dark matter experiments and show that the largest $σ(χp)$ also arise from the HPs and further that the HPs and some of the other patterns are beginning to be constrained by the most recent data from CDMS and from Xenon10 experiments. Finally, it is shown that the prospects are bright for the discovery of dark matter with $σ(χp)$ in the range $10^{-44\pm .5}$cm$^2$ due to a "Wall" consisting of a copious number of parameter points in the Chargino Patterns (CPs) where the chargino is the NLSP. The Wall, which appears in all models considered (mSUGRA, NUSUGRA and D branes) and runs up to about a TeV in LSP mass, significantly enhances the chances for the observation of dark matter by SuperCDMS, ZEPLIN-MAX, or LUX experiments which are expected to achieve a sensitivity of $10^{-45}$ cm$^2$ or more.

hep-ph↗

arXiv2008

CP Violation From Standard Model to Strings

A review of CP violation from the Standard Model to strings is given which includes a broad landscape of particle physics models, encompassing the non-supersymmetric 4D extensions of the standard model, and models based on supersymmetry, on extra dimensions, on strings and on branes. The supersymmetric models discussed include complex mSUGRA and its extensions, while the models based on extra dimensions include 5D models including models based on warped geometry. CP violation beyond the standard model is central to achieving the desired amount of baryon asymmetry in the universe via baryogenesis and leptogenesis. They also affect a variety of particle physics phenomena: electric dipole moments, $g-2$, relic density and detection rates for neutralino dark matter in supersymmetric theories, Yukawa unification in grand unified and string based models, and sparticle production cross sections, and their decays patterns and signatures at hadron colliders. Additionally CP violations can generate CP even-CP odd Higgs mixings, affect the neutral Higgs spectrum and lead to phenomena detectable at colliders. Prominent among these are the CP violation effects in decays of neutral and charged Higgs bosons. Neutrino masses introduce new sources of CP violation which will be explored in neutrino factories in the future. Such phases can also enter in proton stability in unified models of particle interactions. The current experimental status of CP violation is discussed and possibilities for the future outlined.

hep-ph↗

arXiv2008

The Landscape of Sparticle Mass Hierarchies and Their Signature Space at the LHC

The minimal supersymmetric standard model with soft breaking has a large landscape of supersymmetric particle mass hierarchies. This number is reduced significantly in well-motivated scenarios such as minimal supergravity and alternatives. We carry out an analysis of the landscape for the first four lightest particles and identify at least 16 mass patterns, and provide benchmarks for each. We study the signature space for the patterns at the CERN Large Hadron Collider by analyzing the lepton + (jet $\geq 2$) + missing $P_T$ signals with 0, 1, 2 and 3 leptons. Correlations in missing $P_T$ are also analyzed. It is found that even with 10 fb$^{-1}$ of data a significant discrimination among patterns emerges

hep-ph↗

arXiv2007

Suppression of Higgsino mediated proton decay by cancellations in GUTs and strings

A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories (GUTs) and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (anti-triplets) with charges $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an SU(5) model with $45_H+\bar{45}_H$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ Higgs color triplets (anti-triplets) and simple constraints allow for a complete suppression of Higgsino mediated proton decay. Suppression of proton decay in an SU(5) model with Planck scale contributions is also considered. The suppression mechanism is then exhibited for an SO(10) model with a unified Higgs structure involving $144_H+\bar{144}_H$ representations.The SU(5) decomposition of $144_H+\bar{144}_H$ contains $5_H+\bar 5_H$ and $45_H+\bar{45}_H$ and the cancellation mechanism arises among these contributions which mirrror the SU(5) case. The cancellation mechanism appears to be more generally valid for a larger class of unification models. Specifically the cancellation mechanism may play a role in string model constructions to suppress proton decay from dimension five operators. The mechanism allows for the suppression of proton decay consistent with current data allowing for the possibility that proton decay may be visible in the next round of nucleon stability experiment.

hep-ph↗

arXiv2007

Scalar modifications to gravity from unparticle effects may be testable

Interest has focussed recently on low energy implications of a nontrivial scale invariant sector of an effective field theory with an IR fixed point, manifest in terms of ``unparticles'' with peculiar properties. If unparticle stuff exists it could couple to the stress tensor and mediate a new 'fifth' force which we call 'ungravity' arising from the exchange of unparticles between massive particles, which in turn could modify the inverse square law. Under the assumption of strict conformal invariance in the hidden sector down to low energies, we compute the lowest order ungravity correction to the Newtonian gravitational potential and find scale invariant power law corrections of type $(R_{G}/r)^{2d_{\cal U} -1}$ where $d_{\cal U}$ is an anomalous unparticle dimension and $R_{G}$ is a characteristic length scale where the ungravity interactions become significant. $d_{\cal U}$ is constrained to lie the range $ d_{\cal U} > 3 (2)$ for a spin 2 (spin 0) unparticle coupling to the stress tensor (and its trace) and leads to modification of the inverse square law with $r$ dependence in the range between $1/r^{4+2δ} (δ>0)$, while extra dimension models with warping modify the force law with corrections beginning with terms O$(1/r^3)$ for small $r$ but exponentially suppressed for large $r$. Thus a discrimination between extra dimension models and ungravity is possible in future improved submillimeter tests of gravity.

hep-ph↗

arXiv2007

The Stueckelberg $Z'$ Extension with Kinetic Mixing and Milli-Charged Dark Matter From the Hidden Sector

An analysis is given of the Stueckelberg extension of the Standard Model with a hidden sector gauge group $U(1)_X$ where the mass growth for the extra gauge boson occurs via the Stueckelberg mechanism, and where the kinetic mixing in the $U(1)_X\times U(1)_Y$ sector is included. Such a kinetic mixing is generic in a broad class of supergravity and string models. We carry out a detailed global fit of the model with the precision LEP data on and off the $Z$ pole, with $χ^2$ within 1% of the $χ^2$ of the Standard Model fit. Further, it is shown that in the absence of matter in the hidden sector, there is a single effective parameter that controls the deviations from the Standard Model predictions, and the dependence on the kinetic mixing emerges only when matter in the hidden sector is included. An analysis is also given of milli-charged dark matter arising from the hidden sector, where it is shown that such dark matter from the Stueckelberg extension can satisfy WMAP-3 data while allowing for a sharp $Z'$ resonance which can be detected at the Tevatron and at the LHC via a dilepton signal generated by the Drell-Yan process.

hep-ph↗

arXiv2007

The Stueckelberg Extension and Milli Weak and Milli Charge Dark Matter

A overview is given of the recent developments in the $U(1)_X$ Stueckelberg extensions of the Standard Model and of MSSM where all the Standard Model particles are neutral under the $U(1)_X$ but an axion which is absorbed is charged under both $U(1)_X$ and $U(1)_Y$ and acts as the connector field coupling the Standard Model sector with the Stueckelberg sector. Coupled with the usual Higgs mechanism that breaks the $SU(2)_L\times U(1)_Y$ gauge symmetry, this scenario produces mixings in the neutral gauge boson sector generating an extra $Z'$ boson. The couplings of the extra $Z'$ to the Standard Model particles are milli weak but its couplings to the hidden sector matter, defined as matter that couples only to the gauge field of $U(1)_X$, can be of normal electro-weak strength. It is shown that such extensions, aside from the possibility of leading to a sharp $Z' $ resonance, lead to two new types of dark matter: milli weak (or extra weak) and milli charged. An analysis of the relic density shows that the WMAP-3 constraints can be satisfied for either of these scenarios. The types of models discussed could arise as possible field point limit of certain Type IIB orientifold string models.

hep-ph↗

arXiv2007

Proton stability in grand unified theories, in strings, and in branes

A broad overview of the current status of proton stability in unified models of particle interactions is given which includes non - supersymmetric unification, SUSY and SUGRA unified models, unification based on extra dimensions, and string-M-theory models. The extra dimensional unification includes 5D and 6D and universal extra dimensional (UED) models, and models based on warped geometry. Proton stability in a wide array of string theory and M theory models is reviewed. These include Calabi-Yau models, grand unified models with Kac-Moody levels $k>1$, a new class of heterotic string models, models based on intersecting D branes, and string landscape models. The destabilizing effect of quantum gravity on the proton is discussed. The possibility of testing grand unified models, models based on extra dimensions and string-M-theory models via their distinctive modes is investigated. The proposed next generation proton decay experiments, HyperK, UNO, MEMPHYS, ICARUS, LANNDD (DUSEL), and LENA would shed significant light on the nature of unification complementary to the physics at the LHC. Mathematical tools for the computation of proton lifetime are given in the appendices. Prospects for the future are discussed.

hep-ph↗

arXiv2006

Extra-weakly Interacting Dark Matter

We investigate a new type of dark matter with couplings to ordinary matter naturally suppressed by at least one order of magnitude compared to weak interactions. Despite the extra-weak interactions massive particles of this type (XWIMPs) can satisfy the WMAP relic density constraints due to coannihilation if their masses are close to that of the lightest state of the MSSM. The region in the parameter space of a suitably extended mSUGRA model consistent with the WMAP3 constraints on XWIMPs is determined. Plots for sparticles masses are given which can be subject to test at the LHC. We also discuss the sensitivity of the analysis to the top mass. As an example for an explicit model we show that such a form of dark matter can arise in certain $Z'$ extensions of the MSSM. Specifically we consider an abelian extension with spontaneous gauge symmetry breaking via Fayet-Iliopoulos D-terms in the hidden sector. The LSP of the full model arises from the extra $U(1)_X$ sector with extra-weak couplings to Standard Model particles due to experimental constraints. With R-parity conservation the new XWIMP is a candidate for cold dark matter. In a certain limit the model reduces to the \st extension of the MSSM without a Higgs mechanism, and wider ranges of models with similar characteristics are easy to construct.

hep-ph↗

arXiv2006

Dark Matter in SUGRA, Strings and Branes

A brief review is given of dark matter in SUGRA, strings and branes. For SUGRA models the implications of Yukawa coupling unification on dark matter are discussed in the light of $g-2$ and $b\to sγ$ constraints. A brief discussion is given of the dark matter in orbifold string compactifications under constraints of modular invariance and radiative breaking of the electroweak symmetry. Finally a new candidate for dark matter - an extra-weakly interacting massive particle or an XWIMP- is discussed. Such dark matter can arise in a wide class of models, including the Stueckelberg extensions of MSSM, in U(1) extensions of MSSM with off diagonal kinetic energy, and possibly in a wider class of models which may have a string/D-brane origin. Satisfaction of the relic density of XWIMPs consistent with WMAP is also discussed.

hep-ph↗

arXiv2006

An Improved Analysis of $b\to sγ$ in Supersymmetry

An improved analysis of the $b\to s+γ$ decay in the minimal flavor violating case is given taking into account additional contributions in the supersymmetric sector which enter in the next-to-leading-order (NLO) and are enhanced by $\tanβ$ factors. Specifically, we compute a set of twenty one-loop diagrams to give the most complete analysis to date of the NLO supersymmetric corrections. These modifications are computed from the effective charged Higgs and neutral Higgs couplings involving twelve loop diagrams for the charged Higgs sector and eight loop diagrams for the neutral Higgs sector. While the computations of these corrections are available in the literature, their full forms including the complex phase dependence has not be considered. Our analysis takes account of the full allowed set of twenty one-loop diagrams and is more general since it also includes the full dependence on CP phases in non universal sugra and MSSM models. A numerical analysis is carried out to estimate the size of the corrections to $b\to s+γ$. We also briefly discuss the implications of these results for the search for supersymmetry.

hep-ph↗

arXiv2006

Fermion Mass Generation in SO(10) with a Unified Higgs Sector

An analysis of generating fermion masses via cubic couplings in SO(10) grand unification with a unified Higgs sector is given. The new framework utilizes a single pair of vector--spinor representation $144+\bar{144}$ to break the gauge symmetry all the way to $SU(3)_C \times U(1)_{em}$. Typically the matter--Higgs couplings in this framework are quartic and lead to naturally suppressed Yukawa couplings for the first two generations. Here we show that much larger third generation couplings naturally arise at the cubic level with additional matter in 10--plet and 45--plet representations of SO(10). Thus the physical third generation is a mixture of 16, 10 and 45--plet representations while the remaining components become superheavy and are removed from the low energy spectrum. In this scenario it is possible to understand the heaviness of the top in a natural way since the analysis generates a hierarchy in the Yukawa couplings so that $h_{\textnormal {t}}/h_{\textnormal {b}}>> 1$ where $h_{\textnormal {t}} (h_{\textnormal {b}})$ are the top (bottom) Yukawa couplings. It is then possible to realize values of $\tanβ$ as low as 2, which also helps to stabilize the proton.

hep-ph↗