arXiv subjects

Pran Nath

Publications and source records attributed to Pran Nath.

At least 91 records · Page 5Linked to original sources

arXiv2013

Higgs diphoton rate and mass enhancement with vector-like leptons and the scale of supersymmetry

Analysis of contributions from vector-like leptonic supermultiplets to the Higgs diphoton decay rate and to the Higgs boson mass is given. Corrections arising from the exchange of the new leptons and their super-partners, as well as their mirrors are computed analytically and numerically. We also study the correlation between the enhanced Higgs diphoton rate and the Higgs mass corrections. Specifically, we find two branches in the numerical analysis: on the lower branch the diphoton rate enhancement is flat while on the upper branch it has a strong correlation with the Higgs mass enhancement. It is seen that a factor of 1.4-1.8 enhancement of the Higgs diphoton rate on the upper branch can be achieved, and a 4-10 GeV positive correction to the Higgs mass can also be obtained simultaneously. The effect of this extra contribution to the Higgs mass is to release the constraint on weak scale supersymmetry, allowing its scale to be lower than in the theory without extra contributions. The vector-like supermultiplets also have collider implications which can be tested at the LHC and at the ILC.

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arXiv2013

Gluino-driven Radiative Breaking, Higgs Boson Mass, Muon $\mathbf{g-2}$, and the Higgs Diphoton Decay in SUGRA Unification

We attempt to reconcile seemingly conflicting experimental results on the Higgs boson mass, the anomalous magnetic moment of the muon, null results in search for supersymmetry at the LHC within the 8\TeV data and results from $B$-physics, all within the context of supersymmetric grand unified theories. Specifically, we consider a supergravity grand unification model with non-universal gaugino masses where we take the $\mathrm{SU}(3)_C$ gaugino field to be much heavier than the other gaugino and sfermion fields at the unification scale. This construction naturally leads to a large mass splitting between the slepton and squark masses, due to the mass splitting between the electroweak gauginos and the gluino. The heavy Higgs bosons and Higgsinos also follow the gluino toward large masses. We carry out a Bayesian Monte Carlo analysis of the parametric space and find that it can simultaneously explain the large Higgs mass, and the anomalous magnetic moment of the muon, while producing a negligible correction to the Standard Model prediction for $\mathcal{B}r(B^0_s\toμ^+μ^-)$. We also find that the model leads to an excess in the Higgs diphoton decay rate. A brief discussion of the possibility of detection of the light particles is given. Also discussed are the implications of the model for dark matter.

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arXiv2013

Higgs Boson Mass, Proton Decay, Naturalness and Constraints of LHC and Planck Data

A Higgs boson mass $\sim 126$ GeV as determined by the LHC data requires a large loop correction which in turn implies a large sfermion mass. Implication of this result for the stability of the proton in supersymmetric grand unified theories is examined including other experiments constraints along with the most recent result on cold dark matter from Planck. It is shown that over the allowed parameter space of supergravity unified models, proton lifetime is highly sensitive to the Higgs boson mass and a few GeV shift in its mass can change the proton decay lifetime for the mode $p\to \bar νK^+$ by as much as two orders of magnitude or more. An analysis is also given on the nature of radiative breaking of the electroweak symmetry in view of the high Higgs boson, and it is shown that most of the parameter space of universal and non-universal supergravity unified models lies on the Hyperbolic Branch of radiative breaking of the electroweak symmetry, while the Ellipsoidal Branch and the Focal Point regions are highly depleted and contain only a very small region of the allowed parameter space. Also discussed are the naturalness criteria when the proton stability constraints along with the electroweak symmetry breaking are considered together. It is shown that under the assumed naturalness criteria the overall fine tuning is improved for larger values of the scalar mass with the inclusion of the proton stability constraint. Thus the naturalness criteria including proton stability along with electroweak symmetry breaking constraints tend to favor the weak scale of SUSY in the several TeV region. Implications for the discovery of supersymmetry in view of the high Higgs mass are briefly discussed.

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arXiv2013

Perspectives on Higgs Boson and Supersymmetry

We review the recent discovery of the Higgs like particle at $\sim 125$ GeV and its implications for particle physics models. Specifically the implications of the relatively high Higgs mass for the discovery of supersymmetry are discussed. Several related topics such as naturalness and supersymmetry, dark matter and unification are also discussed.

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arXiv2012

Higgs Physics and Supersymmetry

A brief overview of Higgs physics and of supersymmetry is given. The central theme of the overview is to explore the implications of the recent discovery of a Higgs like particle regarding the prospects for the discovery of supersymmetry assuming that it is indeed the spin 0 CP even boson that enters in the spontaneous breaking of the electroweak symmetry. The high mass of the Higgs like boson at $\sim 125$ GeV points to the weak scale of supersymmetry that enters in the loop correction to the Higgs boson mass, to be relatively high, i.e., in the TeV region. However, since more than one independent mass scales enter in softly broken supersymmetry, the allowed parameter space of supersymmetric models can allow a small Higgs mixing parameter $μ$ and light gaugino masses consistent with a $\sim 125$ GeV Higgs boson mass. Additionally some light third generation sfermions, i.e., the stop and the stau are also permissible. Profile likelihood analysis of a class of SUGRA models indicates that $m_A> 300$ GeV which implies one is in the decoupling phase and the Higgs couplings are close to the standard model in this limit. Thus a sensitive measurement of the Higgs couplings with fermions and with the vector bosons is needed to detect beyond the standard model effects. Other topics discussed include dark matter, proton stability, and the Stueckelberg extended models as probes of new physics. A brief discussion of the way forward in the post Higgs discovery era is given.

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arXiv2012

The Development of Supergravity Grand Unification: Circa 1982-85

The development in the early eighties of supergravity grand unified models with gravity mediated breaking of supersymmetry, has led to a remarkable progress in the study of supersymmetry at colliders, in dark matter and in a variety of other experimental searches in the intervening years since that time. The purpose of this note is to review this development and describe our construction of this theory in the period 1982-85.

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arXiv2012

$τ\to μγ$ Decay in Extensions with a Vector Like Generation

An analysis is given of the decay $τ\to μ+ γ$ in MSSM extensions with a vector like generation. Here mixing with the mirrors allows the possibility of this decay. The analysis is done at one loop with the exchange of charginos and neutralinos and of sleptons and mirror sleptons in the loops. It is shown that a branching ratio ${\cal B}(τ\to μ+γ)$ in the range $4.4\times 10^{-8} -10^{-9}$ can be gotten which would be accessible to improved experiment such as at SuperB factories for this decay. The effects of CP violation on this decay are also analyzed.

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arXiv2012

Implications of the Higgs Boson Discovery for mSUGRA

A Bayesian analysis is carried out to identify the consistent regions of the mSUGRA parameter space, where the newly-discovered Higgs boson's mass is used as a constraint, along with other experimental constraints. It is found that $m_{1/2}$ can lie in the sub-TeV region, $A_0/m_0$ is mostly confined to a narrow strip with $|A_0/m_0| \leq 1$, while $m_0$ is typically a TeV or larger. Further, the Bayesian analysis is used to set 95% CL lower bounds on sparticle masses. Additionally, it is shown that the spin independent neutralino-proton cross section lies just beyond the reach of the current sensitivity but within the projected sensitivity of the SuperCDMS-1T and XENON-1T experiments, which explains why dark matter has thus far not been detected. The light sparticle spectrum relevant for the discovery of supersymmetry at the LHC are seen to be the gluino, the chargino and the stop with the gluino and the chargino as the most likely candidates.

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arXiv2012

SUGRA Grand Unification, LHC and Dark Matter

A brief review is given of recent developments related to the Higgs signal and its implications for supersymmetry in the supergravity grand unification framework. The Higgs data indicates that the allowed parameter space largely lies on focal curves and focal surfaces of the Hyperbolic Branch of radiative breaking of the electroweak symmetry where TeV size scalars naturally arise. The high mass of the Higgs leads to a more precise prediction for the allowed range of the spin independent neutralino -proton cross section which is encouraging for the detection of dark matter in future experiments with greater sensitivity. Also discussed is the status of grand unification and a natural solution to breaking the GUT group at one scale and resolving the doublet-triplet problem. It is shown that the cosmic coincidence can be compatible within a supersymmetric framework in a muticomponent dark matter picture with one component charged under $B-L$ while the other component is the conventional supersymmetric dark matter candidate, the neutralino.

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arXiv2012

Cosmic Coincidence and Asymmetric Dark Matter in a Stueckelberg Extension

We discuss the possibility of cogenesis generating the ratio of baryon asymmetry to dark matter in a Stueckelberg U(1) extension of the standard model and of the minimal supersymmetric standard model. For the U(1) we choose $L_μ-L_τ$ which is anomaly free and can be gauged. The dark matter candidate arising from this extension is a singlet of the standard model gauge group but is charged under $L_μ-L_τ$. Solutions to the Boltzmann equations for relics in the presence of asymmetric dark matter are discussed. It is shown that the ratio of the baryon asymmetry to dark matter consistent with the current WMAP data, i.e., the cosmic coincidence, can be successfully explained in this model with the depletion of the symmetric component of dark matter from resonant annihilation via the Stueckelberg gauge boson. For the extended MSSM model it is shown that one has a two component dark matter picture with asymmetric dark matter being the dominant component and the neutralino being the subdominant component (i.e., with relic density a small fraction of the WMAP cold dark matter value). Remarkably, the subdominant component can be detected in direct detection experiments such as SuperCDMS and XENON-100. Further, it is shown that the class of Stueckelberg models with a gauged $L_μ-L_τ$ will produce a dramatic signature at a muon collider with the $σ(μ^+μ^-\to μ^+μ^-,τ^+τ^-)$ showing a detectable $Z'$ resonance while $σ(μ^+μ^-\to e^+e^-)$ is devoid of this resonance. Asymmetric dark matter arising from a $U(1)_{B-L}$ Stueckelberg extension is also briefly discussed. Finally, in the models we propose the asymmetric dark matter does not oscillate and there is no danger of it being washed out from oscillations.

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arXiv2012

GUT and Supersymmetry at the LHC and in dark matter

Conventional SO(10) models involve more than one scale for a complete breaking of the GUT symmetry requiring further assumptions on the VEVs of the Higgs fields that enter in the breaking to achieve viable models. Recent works where the breaking can be accomplished at one scale are discussed. These include models with just a pair of $144+\bar{144}$ of Higgs fields. Further extensions of this idea utilizing $560+ \bar{560}$ of Higgs representations allow both the breaking at one scale, as well as accomplish a natural doublet-triplet splitting via the missing partner mechanism. More generally, we discuss the connection of high scale models to low energy physics in the context of supergravity grand unification. Here we discuss a natural solution to the little hierarchy problem and also discuss the implications of the LHC data for supersymmetry. It is shown that the LHC data implies that most of the parameter space of supergravity models consistent with the data lie on the Hyperbolic Branch of radiative breaking of the electroweak symmetry and more specifically on the Focal Surface of the Hyperbolic Branch. A discussion is also given of the implications of recent LHC data on the Higgs boson mass for the discovery of supersymmetry and for the search for dark matter.

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arXiv2011

Variety of SO(10) GUTs with Natural Doublet-Triplet Splitting via the Missing Partner Mechanism

We present a new class of unified SO(10) models where the GUT symmetry breaking down to the standard model gauge group involves just one scale, in contrast to the conventional SO(10) models which require two scales. Further, the models we discuss possess a natural doublet-triplet splitting via the missing partner mechanism without fine tuning. Such models involve $560+\ov{560}$ pair of heavy Higgs fields along with a set of light fields. The $560+\ov{560}$ are the simplest representations of SO(10) besides the $126+\ov{126}$ which contain an excess of color triplets over $SU(2)_L$ doublets. We discuss several possibilities for realizing the missing partner mechanism within these schemes. With the $126+\ov{126}$ multiplets, three viable models are found with additional fields belonging to ${210 + 2 \times 10 + 120}$, ${45 + 10 + 120}$, or ${210 + 16 + \ov{16} + 10 + 120}$. With the $560+\ov{560}$, a unique possibility arises for the missing partner mechanism, with additional ${2\times 10+ 320}$ fields. These models are developed in some detail. It is shown that fully realistic fermion masses can arise in some cases, while others can be made realistic by addition of vector--like representations. Naturally large neutrino mixing angles, including sizable $θ_{13}$, can emerge in these models. The couplings of the $H_u(H_d)$ Higgs doublets of the MSSM which give masses to the up quarks (down quarks and leptons) are not necessarily equal at the grand unification scale and would lead to a new phenomenology at the low energy scales.

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arXiv2011

Higgs Boson Mass Predictions in SUGRA Unification, Recent LHC-7 Results, and Dark Matter

LHC-7 has narrowed down the mass range of the light Higgs boson. This result is consistent with the supergravity unification framework, and the current Higgs boson mass window implies a rather significant loop correction to the tree value pointing to a relatively heavy scalar sparticle spectrum with universal boundary conditions. It is shown that the largest value of the Higgs boson mass is obtained on the Hyperbolic Branch of radiative breaking. The implications of light Higgs boson in the broader mass range of 115 GeV to 131 GeV and a narrower range of 123 GeV to 127 GeV are explored in the context of the discovery of supersymmetry at LHC-7 and for the observation of dark matter in direct detection experiments.

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arXiv2011

Naturalness, Supersymmetry and Implications for LHC and Dark Matter

It is shown that the Hyperbolic Branch of the radiative electroweak symmetry breaking contains in it three regions: the Focal Point, Focal Curves, and Focal Surfaces. Further, the Focal Point is shown to lie on the boundary of a Focal Curve. These focal regions allow for a small $μ$ while scalar masses can become large and may lie in the several TeV region. It is shown that for the mSUGRA model the current LHC-7 constraint depletes the Focal Point region while regions on Focal Curves and Focal Surfaces remain largely intact. The LHC implications for models which lie on Focal Curves are briefly discussed as well as the implications of dark matter constraints for the Focal Point, Focal Curves and Focal Surfaces are discussed.

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arXiv2011

R-parity Conservation via the Stueckelberg Mechanism: LHC and Dark Matter Signals

We investigate the connection between the conservation of R-parity in supersymmetry and the Stueckelberg mechanism for the mass generation of the B-L vector gauge boson. It is shown that with universal boundary conditions for soft terms of sfermions in each family at the high scale and with the Stueckelberg mechanism for generating mass for the B-L gauge boson present in the theory, electric charge conservation guarantees the conservation of R-parity in the minimal B-L extended supersymmetric standard model. We also discuss non-minimal extensions. This includes extensions where the gauge symmetries arise with an additional U(1)_{B-L} x U(1)_X, where U(1)_X is a hidden sector gauge group. In this case the presence of the additional U(1)_X allows for a Z' gauge boson mass with B-L interactions to lie in the sub-TeV region overcoming the multi-TeV LEP constraints. The possible tests of the models at colliders and in dark matter experiments are analyzed including signals of a low mass Z' resonance and the production of spin zero bosons and their decays into two photons. In this model two types of dark matter candidates emerge which are Majorana and Dirac particles. Predictions are made for a possible simultaneous observation of new physics events in dark matter experiments and at the LHC.

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arXiv2011

Excess Observed in CDF $B^0_s \to μ^{+} μ^{-}$ and SUSY at the LHC

The recent excess observed by CDF in $B^0_s \to μ^{+} μ^{-}$ is interpreted in terms of a possible supersymmetric origin. An analysis is given of the parameter space of mSUGRA and non-universal SUGRA models under the combined constraints from LHC-7 with 165 pb$^{-1}$ of integrated luminosity, under the new XENON-100 limits on the neutralino-proton spin independent cross section and under the CDF $B^0_s \to μ^{+} μ^{-}$ 90% C.L. limit reported to arise from an excess number of dimuon events. It is found that the predicted value of the branching ratio $B^0_s \to μ^{+} μ^{-}$ consistent with all the constraints contains the following set of NLSPs: chargino, stau, stop or CP odd (even) Higgs. The lower bounds of sparticles, including those from the LHC, XENON and CDF $B^0_s\to μ^+μ^-$ constraint, are exhibited and the shift in the allowed range of sparticle masses arising solely due to the extra constraint from the CDF result is given. It is pointed out that the two sided CDF 90% C.L. limit puts upper bounds on sparticle masses. An analysis of possible signatures for early discovery at the LHC is carried out corresponding to the signal region in $B^0_s \to μ^{+} μ^{-}$. Implications of GUT-scale non-universalities in the gaugino and Higgs sectors are discussed. If the excess seen by the CDF Collaboration is supported by further data from LHCb or D0, this new result could be a harbinger for the discovery of supersymmetry.

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arXiv2011

An Explanation of the CDF Dijet Anomaly within a $U(1)_X$ Stueckelberg Extension

We discuss the recent excess seen by the CDF Collaboration in the dijet invariant mass distribution produced in association with a $W$ boson. We analyze the possibility of such a signal within the context of a $U(1)_X$ Stueckelberg extension of the Standard Model where the new gauge boson couples only to quarks. In addition to the analysis of the $Wjj$ anomaly we also discuss the production of $Zjj$ and $γjj$ at the Tevatron. The analysis is then extended to the Large Hadron Collider with $\sqrt{s}=7 {\rm TeV}$ and predictions for the dijet signals are made.

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arXiv2011

The Chromoelectric Dipole Moment of the Top Quark in Models with Vector Like Multiplets

The chromoelectric dipole moment of the top quark is calculated in a model with a vector like multiplet which mixes with the third generation in an extension of the MSSM. Such mixings allow for new CP violating phases. Including these new CP phases, the chromoelectric dipole moment that generates an electric dipole of the top in this class of models is computed. The top chromoelectric dipole moment operator arises from loops involving the exchange of the W, the Z as well as from the exchange involving the charginos, the neutralinos, the gluino, and the vector like multiplet and their superpartners. The analysis of the chromoelectric dipole moment operator of the top is more complicated than for the light quarks because the mass of the external fermion, in this case the top quark mass, cannot be ignored relative to the masses inside the loops. A numerical analysis is presented and it is shown that the contribution to the top EDM could lie in the range ($10^{-19}-10^{-18})$ ecm consistent with the current limits on the EDM of the electron, the neutron and on atomic EDMs. A top EDM of size $(10^{-19}-10^{-18})$ ecm could be accessible in collider experiments such as at the LHC and at the ILC.

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