arXiv subjects

Bhaskar Dutta

Publications and source records attributed to Bhaskar Dutta.

At least 181 records · Page 10Linked to original sources

arXiv2012

Non-thermal Higgsino Dark Matter: Cosmological Motivations and Implications for a 125 GeV Higgs

If the lightest supersymmetric particle (LSP) is Higgsino-like, the thermal relic density is lower than the observed dark matter content for a LSP mass in the sub-TeV region. We outline constraints arising from the Fermi Gamma-Ray Telescope data and LSP production from gravitino decay that must be satisfied by a successful non-thermal Higgsino scenario. We show that in a generic class of models where anomaly and modulus mediated contributions to supersymmetry breaking are of comparable size, Higgsino arises as the only viable sub-TeV dark matter candidate if gravitinos are heavy enough to decay before the onset of big bang nucleosynthesis (BBN). The correct relic density can be obtained via modulus decay in these models. As an explicit example, we consider a modulus sector in effective field theory ($D=4, N=1$ supergravitiy arising from type IIB KKLT compactification). Within this class of mirage mediation models, heaviness of the gravitino forces a sub-TeV Higgsino LSP and gives a Higgs mass around 125 GeV. In this example, the constraints from direct detection experiments are also satisfied.

hep-ph↗

arXiv2012

Attractors, Universality and Inflation

Studies of the initial conditions for inflation have conflicting predictions from exponential suppression to inevitability. At the level of phase space, this conflict arises from the competing intuitions of CPT invariance and thermodynamics. After reviewing this conflict, we enlarge the ensemble beyond phase space to include scalar potential data. We show how this leads to an important contribution from inflection point inflation, enhancing the likelihood of inflation to an inverse cubic power law. In the process, we emphasize the attractor dynamics of the gravity-scalar system and the existence of universality classes from inflection point inflation. Finally, we comment on the predictivity of inflation in light of these results.

hep-th↗

arXiv2012

Lepton Flavor Violation at the Large Hadron Collider

We investigate a potential of discovering lepton flavor violation (LFV) at the Large Hadron Collider. A sizeable LFV in low energy supersymmetry can be induced by massive right-handed neutrinos, which can explain neutrino oscillations via the seesaw mechanism. We investigate a scenario where the distribution of an invariant mass of two hadronically decaying taus ($\tauh\tauh$) from $\schizero{2}$ decays is the same in events with or without LFV. We first develop a transfer function using this ditau mass distribution to model the shape of the non-LFV $\tauhμ$ invariant mass. We then show the feasibility of extracting the LFV $\tauhμ$ signal. The proposed technique can also be applied for a LFV $\tauh e$ search.

hep-ph↗

arXiv2012

θ_{13} and Proton Decay in a Minimal SO(10) x S_4 model of Flavor

In a recent paper, a minimal supersymmetric (SUSY) SO(10)xS_4 based unified model of flavor for quarks and leptons was proposed with two 10 and one 126 contributing to fermion masses. An important aspect of this model is that Yukawa couplings emerge dynamically from minimization of the flavon potential, thereby reducing the number of parameters considerably. We make a detailed numerical analysis of this model for fermion mixings including SUSY threshold effects at the TeV scale and type-I corrections to a type-II dominant seesaw for neutrino masses. This is a single-step breaking model with SUSY SO(10) broken at the Grand Unified Theory (GUT)-scale of 2x10^16 GeV to the Minimal Supersymmetric Standard Model (MSSM). The minimal model has only 11 parameters, and therefore, the charged fermion fits predict the masses (up to an overall scale) and mixings in the neutrino sector. We present correlations for the different predictions in the neutrino mixing parameters. The recent experimental "large" θ_{13} value of \sim 9 degrees can be obtained by a simple extension of the minimal model. We also find that proton decay mode p -> K^+\barν_μhas a partial lifetime of \sim10^34 yrs, which is within reach of the next round of planned proton decay searches. The successful fit for fermion masses requires the Higgs mass to be below 129 GeV in this model. If the Higgs mass lies between 120-128 GeV, as suggested by the recent LHC data, we find a lower limit on the light stop mass of 755 (211) GeV for μ>0 (<0).

hep-ph↗

arXiv2012

Searching for Top Squarks at the LHC in Fully Hadronic Final State

We pursue a scenario where the lighter top squark (stop) mass is accessible for the Large Hadron Collider (LHC) in the near future, while gluinos and first two generation squarks are heavier. At $\sqrt{s} = 8$ TeV, we investigate the identification of stops which decay predominantly into a top quark and the stable lightest supersymmetric particle. We use a simple kinematical variable, $M3$, to reconstruct two top quarks which are pair-produced from the stops, in the fully hadronic channel. The dominant Standard Model (SM) background for this signal stems from $t\bar t$ plus jets, with one top quark decaying into $ blν$, where the lepton is undetected and the $ν$ produces missing transverse momentum. The lepton identification efficiency is thus crucial in order to estimate the background correctly. We identify kinematical variables to reduce the SM background. We find that it is possible to achieve signal and background cross-section at similar levels for stop masses around $350 - 500$ GeV for a neutralino mass of 100 GeV.

hep-ph↗

arXiv2012

Holomorphic Bisectional Curvatures, Supersymmetry Breaking, and Affleck-Dine Baryogenesis

Working in $D=4, N=1$ supergravity, we utilize relations between holomorphic sectional and bisectional curvatures of Kahler manifolds to constrain Affleck-Dine baryogenesis. We show the following No-Go result: Affleck-Dine baryogenesis cannot be performed if the holomorphic sectional curvature at the origin is isotropic in tangent space; as a special case, this rules out spaces of constant holomorphic sectional curvature (defined in the above sense) and in particular maximally symmetric coset spaces. We also investigate scenarios where inflationary supersymmetry breaking is identified with the supersymmetry breaking responsible for mass splitting in the visible sector, using conditions of sequestering to constrain manifolds where inflation can be performed.

hep-th↗

arXiv2012

Diagnosis of Supersymmetry Breaking Mediation Schemes by Mass Reconstruction at the LHC

If supersymmetry is discovered at the LHC, the next question will be the determination of the underlying model. While this may be challenging or even intractable, a more optimistic question is whether we can understand the main contours of any particular paradigm of the mediation of supersymmetry breaking. The determination of superpartner masses through endpoint measurements of kinematic observables arising from cascade decays is a powerful diagnostic tool. In particular, the determination of the gaugino sector has the potential to discriminate between certain mediation schemes (not all schemes, and not between different UV realizations of a given scheme). We reconstruct gaugino masses, choosing a model where anomaly contributions to supersymmetry breaking are important (KKLT compactification), and find the gaugino unification scale. Moreover, reconstruction of other superpartner masses allows us to solve for the parameters defining the UV model. The analysis is performed in the stop and stau coannihilation regions where the lightest neutralinos are mainly gauginos, to additionally satisfy dark matter constraints. We thus develop observables to determine stau and stop masses to verify that the coannihilation mechanism is indeed operational, and solve for the relic density.

hep-ph↗

arXiv2011

Extragalactic and galactic gamma-rays and neutrinos from annihilating dark matter

We describe cosmic gamma-ray and neutrino signals of dark matter annihilation, explaining how the complementarity of these signals provides additional information that, if observable, can enlighten the particle nature of dark matter. This is discussed in the context of exploiting the separate galactic and extragalactic components of the signal, using the spherical halo model distribution of dark matter. We motivate the discussion with supersymmetric extensions of the standard model of particle physics. We consider the minimal supersymmetric standard model (MSSM) where both neutrinos and gamma-rays are produced from annihilations. We also consider a gauged B-L, baryon number minus lepton number, extension of the MSSM, where annihilation can be purely to heavy right-handed neutrinos. We compare the galactic and extragalactic components of these signals, and conclude that it is not yet clear which may dominate when looking out of the galactic plane. To answer this question, we must have an understanding of the contribution of halo substructure to the annihilation signals. We find that different theories with indistinguishable gamma-ray signals can be distinguished in the neutrino signal. Gamma-ray annihilation signals are difficult to observe from the galactic center, due to abundant astrophysical sources; but annihilation neutrinos from there would not be so hidden, if they can be observed over the atmospheric neutrinos produced by cosmic rays.

hep-ph↗

arXiv2011

Catastrophic Inflation

We study inflection point inflation using Singularity Theory, which relates degenerate critical points of functions to their local behavior. This approach illuminates universal features of small-field models and gives analytic control over parametrized families of scalar potentials near inflationary solutions. The behavior of the scalar potential is tied to the number of physical input parameters, which determines a set of universality classes. Within these classes, we obtain universal scaling relations for density perturbations and the scale of inflation. In specific models, we show that the scale of supersymmetry breaking also possesses scaling behavior. We illustrate this general structure with a specific example: the Racetrack Inflation model in type IIB string theory, with the inflaton being the real part of the Kahler modulus, and the input parameters being flux dependent quantities that appear in the 4D, N=1 superpotential.

hep-th↗

arXiv2011

Bi-Event Subtraction Technique at Hadron Colliders

We propose the Bi-Event Subtraction Technique (BEST) as a method of modeling and subtracting large portions of the combinatoric background during reconstruction of particle decay chains at hadron colliders. The combinatoric background arises when it is impossible to know experimentally which observed particles come from the decay chain of interest. The background shape can be modeled by combining observed particles from different collision events and be subtracted away, greatly reducing the overall background. This idea has been demonstrated in various experiments in the past. We generalize it by showing how to apply BEST multiple times in a row to fully reconstruct a cascade decay. We show the power of BEST with two simulated examples of its application towards reconstruction of the top quark and a supersymmetric decay chain at the Large Hadron Collider.

hep-ph↗

arXiv2011

B_s --> mu+mu- in Supersymmetric Grand Unified Theories

We investigate the recent CDF measurement of the Br(B_s --> mu+mu-) which shows excess over the Standard Model. We consider minimal supergravity motivated models (mSUGRA)/CMSSM and grand unified models, SU(5) and SO(10). In the grand unified models, the neutrino mixings provide an additional source of squark flavor violation through the quark-lepton unification. In the context of minimal SU(5) model, we find that the new CDF measurement has imposed a lower bound on the branching ratio of tau --> mu gamma for a large CP phase in the B_s-bar B_s mixing. Recall that there have been indication for a large CP phase in B_s mixing from B_s --> J/psi phi (Tevatron and LHCb) and dimuon asymmetry (D0). We also predict Br(tau --> mu eta) for the possible range of values of Br(tau --> mu gamma).

hep-ph↗

arXiv2011

Constructing Flat Inflationary Potentials in Supersymmetry

We show that in supersymmetry one can obtain inflationary potentials in the observable sector that are sufficiently flat at sub-Planckian field values. Structure of the supersymmetric scalar potential along a flat direction combined with the existence of higher order terms in an effective field theory expansion allows one to find scales below the effective field theory cut off where two or a higher number of the potential derivatives may vanish. As an explicit example, we demonstrate that inflection point inflation within a broad range of scales O(TeV) << H < 3 x 10^9 GeV can be accommodated within weak scale supersymmetry. The fine tuning of model parameters needed for successful inflation is considerably improved in this scenario.

hep-th↗

arXiv2011

Effects of P-wave Annihilation on the Angular Power Spectrum of Extragalactic Gamma-rays from Dark Matter Annihilation

We present a formalism for estimating the angular power spectrum of extragalactic gamma-rays produced by dark matter annihilating with any general velocity-dependent cross section. The relevant density and velocity distribution of dark matter is modeled as an ensemble of smooth, universal, rigid, disjoint, spherical halos with distribution and universal properties constrained by simulation data. We apply this formalism to theories of dark matter with p-wave annihilation, for which the relative-velocity-weighted annihilation cross section is σv=a+bv^2. We determine that this significantly increases the gamma-ray power if b/a >> 10^6. The effect of p-wave annihilation on the angular power spectrum is very similar for the sample of particle physics models we explored, suggesting that the important effect for a given b/a is largely determined by the cosmic dark matter distribution. If the dark matter relic from strong p-wave theories is thermally produced, the intensities of annihilation gamma-rays are strongly p-wave suppressed, making them difficult to observe. If an angular power spectrum consistent with a strong p-wave were to be observed, it would likely indicate non-thermal production of dark matter in the early Universe.

astro-ph.HE↗

arXiv2011

Dimuon CP Asymmetry in B Decays and Wjj Excess in Two Higgs Doublet Models

We analyze the puzzle of the dimuon CP asymmetry in B_s decays in two Higgs doublet models. We show that the flavor changing neutral current (FCNC) induced by the Higgs coupling in a type III two Higgs doublet model provides a solution to the dimuon charge asymmetry puzzle by enhancing the absorbtive part of the mixing amplitude Γ_{12}^s. We investigate different experimental constraints and show that it is possible to enhance Γ_{12}^s in order to explain the dimuon asymmetry observed by D0. This enhancement requires large Higgs couplings to the first and second generations of quarks which may also explain the recent 3.2 σWjj excess observed by CDF.

hep-ph↗

arXiv2011

Asymmetric Dark Matter from Hidden Sector Baryogenesis

We consider the production of asymmetric dark matter during hidden sector baryogenesis. We consider a particular supersymmetric model where the dark matter candidate has a number density approximately equal to the baryon number density, with a mass of the same scale as the $b$, $c$ and $τ$. Both baryon asymmetry and dark matter are created at the same time in this model. We describe collider and direct detection signatures of this model.

hep-ph↗

arXiv2010

Determination of Non-Universal Supergravity Models at the Large Hadron Collider

We examine a well motivated non-universal supergravity model where the Higgs boson masses are not unified with the other scalars at the grand unified scale at the LHC. The dark matter content can easily be satisfied in this model by having a larger Higgsino component in the lightest neutralino. Typical final states in such a scenario at the LHC involve W bosons. We develop a bi-event subtraction technique to remove a huge combinatorial background to identify W -> jj decays. This is also a key technique to reconstruct supersymmetric particle masses in order to determine the model parameters. With the model parameters, we find that the dark matter content of the universe can be determined in agreement with existing experimental results.

hep-ph↗

arXiv2010

Cladogenesis: Baryon-Dark Matter Coincidence from Branchings in Moduli Decay

We propose late-time moduli decay as the common origin of baryons and dark matter. The baryon asymmetry is produced from the decay of new TeV scale particles, while dark matter is created from the (chain) decay of R-parity odd particles without undergoing any annihilation. The baryon and dark matter abundances are mainly controlled by the dilution factor from moduli decay, which is typically in the range 10^{-9}-10^{-7}. The exact number densities are determined by simple branching fractions from modulus decay, which are expected to be of similar order in the absence of symmetries. This scenario can naturally lead to the observed baryon asymmetry and, for moderate suppression of the two-body decays of the modulus to R-parity odd particles, can also yield the correct dark matter abundance for a dark matter mass in the (5-500) GeV range.

hep-ph↗

arXiv2010

Schizophrenic Neutrinos and $ν$-less Double Beta Decay

We point out a novel possibility for neutrinos where all neutrino flavors can be part Dirac and part Majorana. Our primary motivation for this model comes from an attempt to use supersymmetric see-saw models to tie inflation, baryon asymmetry of the Universe and dark matter to the neutrino sector. The idea however could stand on its own, with or without supersymmetry. We present a realization of this possibility within an $S_3$ family symmetry for neutrino masses, where we obtain tri-bi-maximal mixing for neutrinos to the leading order. The model predicts that for the case of inverted hierarchy, the lower limit on the neutrino mass measured in neutrinoless double beta decay experiments is about a factor of two larger than the usual case.

hep-ph↗