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Publications and Pre-prints

Below is a list of all of the publications and pre-prints attributed to me on the arXiv. You can find my citation statistics on Inspire-Hep or on Google Scholar.

June 29, 2017

Electroweak baryogenesis in the Z3-invariant NMSSM

Sujeet Akula, Csaba Balázs, Liam Dunn, Graham White

We calculate the baryon asymmetry of the Universe in the Z3-invariant Next-to-Minimal Supersymmetric Standard Model where the interactions of the singlino provide the necessary source of charge and parity violation. Using the closed time path formalism, we derive and solve transport equations for the cases where the singlet acquires a vacuum expectation value (VEV) before and during the electroweak phase transition. We perform a detailed scan to show how the baryon asymmetry varies throughout the relevant parameter space. Our results show that the case where the singlet acquires a VEV during the electroweak phase transition typically generates a larger baryon asymmetry, although we expect that the case where the singlet acquires a VEV first is far more common for any model in which parameters unify at a high scale. Finally, we examine the dependence of the baryon asymmetry on the three-body interactions involving gauge singlets.

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July 29, 2016

Semi-analytic techniques for calculating bubble wall profiles

Sujeet Akula, Csaba Balázs, Graham A. White

We present semi-analytic techniques for finding bubble wall profiles during first order phase transitions with multiple scalar fields. Our method involves reducing the problem to an equation with a single field, finding an analytic solution and perturbing around it. The perturbations can be written in a semi-analytic form. We argue that our technique lacks convergence problems and demonstrate the speed of convergence on an example potential.

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October 18, 2014

Sparticle Mass Hierarchies, Simplified Models from SUGRA Unification, and Benchmarks for LHC Run-II SUSY Searches

David Francescone, Sujeet Akula, Baris Altunkaynak, Pran Nath

Sparticle mass hierarchies contain significant information regarding the origin and nature of supersymmetry breaking. The hierarchical patterns are severely constrained by electroweak symmetry breaking as well as by the astrophysical and particle physics data. They are further constrained by the Higgs boson mass measurement. The sparticle mass hierarchies can be used to generate simplified models consistent with the high scale models. In this work we consider supergravity models with universal boundary conditions for soft parameters at the unification scale as well as supergravity models with nonuniversalities and delineate the list of sparticle mass hierarchies for the five lightest sparticles. Simplified models can be obtained by a truncation of these, retaining a smaller set of lightest particles. The mass hierarchies and their truncated versions enlarge significantly the list of simplified models currently being used in the literature. Benchmarks for a variety of supergravity unified models appropriate for SUSY searches at future colliders are also presented. The signature analysis of two benchmark models has been carried out and a discussion of the searches needed for their discovery at LHC RUN-II is given. An analysis of the spin independent neutralino-proton cross section exhibiting the Higgs boson mass dependence and the hierarchical patterns is also carried out. It is seen that a knowledge of the spin independent neutralino-proton cross section and the neutralino mass will narrow down the list of the allowed sparticle mass hierarchies. Thus dark matter experiments along with analyses for the LHC Run-II will provide strong clues to the nature of symmetry breaking at the unification scale.

Published in JHEP 1501 (2015) 158 arΧiv pdf doi

April 19, 2013

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

Sujeet Akula, Pran Nath

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 $\mathcal{B}r(B^0_s\to\mu^+\mu^-)$. 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.

Published in Phys. Rev. D 87, 115022 (2013) arΧiv pdf doi

July 8, 2012

Implications of the Higgs Boson Discovery for mSUGRA

Sujeet Akula, Pran Nath, Gregory Peim

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.

Published in Phys. Lett. B 717 (2012) 188-192 arΧiv pdf doi

December 15, 2011

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

Sujeet Akula, Baris Altunkaynak, Daniel Feldman, Pran Nath, Gregory Peim

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.

Published in Phys.Rev.D85:075001,2012 arΧiv pdf doi

November 19, 2011

Naturalness, Supersymmetry and Implications for LHC and Dark Matter

Sujeet Akula, Mengxi Liu, Pran Nath, Gregory Peim

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 $\mu$ 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.

Published in Phys.Lett.B709:192-199,2012 arΧiv pdf doi

July 18, 2011

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

Sujeet Akula, Daniel Feldman, Pran Nath, Gregory Peim

The recent excess observed by CDF in $B^0_s \to \mu^{+} \mu^{-}$ 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 $B^0_s \to \mu^{+} \mu^{-}$ 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 $B^0_s \to \mu^{+} \mu^{-}$ 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 $B^0_s\to \mu^+\mu^-$ 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 $B^0_s \to \mu^{+} \mu^{-}$. 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.

Published in Phys.Rev.D84:115011,2011 arΧiv pdf doi

March 25, 2011

New Constraints on Dark Matter from CMS and ATLAS Data

Sujeet Akula, Daniel Feldman, Zuowei Liu, Pran Nath, Gregory Peim

Constraints on dark matter from the first CMS and ATLAS SUSY searches are investigated. It is shown that within the minimal supergravity model, the early search for supersymmetry at the LHC has depleted a large portion of the signature space in dark matter direct detection experiments. In particular, the prospects for detecting signals of dark matter in the XENON and CDMS experiments are significantly affected in the low neutralino mass region. Here the relic density of dark matter typically arises from slepton coannihilations in the early universe. In contrast, it is found that the CMS and ATLAS analyses leave untouched the Higgs pole and the Hyperbolic Branch/Focus Point regions, which are now being probed by the most recent XENON results. Analysis is also done for supergravity models with non-universal soft breaking where one finds that a part of the dark matter signature space depleted by the CMS and ATLAS cuts in the minimal SUGRA case is repopulated. Thus, observation of dark matter in the LHC depleted region of minimal supergravity may indicate non-universalities in soft breaking.

Published in Mod.Phys.Lett.A26:1521-1535,2011 arΧiv pdf doi

March 7, 2011

Interpreting the First CMS and ATLAS SUSY Results

Sujeet Akula, Ning Chen, Daniel Feldman, Mengxi Liu, Zuowei Liu, Pran Nath, Gregory Peim

The CMS and the ATLAS Collaborations have recently reported on the search for supersymmetry with 35 pb$^{-1}$ of data and have put independent limits on the parameter space of the supergravity unified model with universal boundary conditions at the GUT scale for soft breaking, i.e., the mSUGRA model. We extend this study by examining other regions of the mSUGRA parameter space in $A_0$ and $\tan\beta$. Further, we contrast the reach of CMS and ATLAS with 35 pb$^{-1}$ of data with the indirect constraints, i.e., the constraints from the Higgs boson mass limits, from flavor physics and from the dark matter limits from WMAP. Specifically it is found that a significant part of the parameter space excluded by CMS and ATLAS is essentially already excluded by the indirect constraints and the fertile region of parameter space has yet to be explored. We also emphasize that gluino masses as low as 400 GeV but for squark masses much larger than the gluino mass remain unconstrained and further that much of the hyperbolic branch of radiative electroweak symmetry breaking, with low values of the Higgs mixing parameter $\mu$, is essentially untouched by the recent LHC analysis.

Published in Phys.Lett.B699:377-382,2011 arΧiv pdf doi