arXiv subjects

Bhaskar Dutta

Publications and source records attributed to Bhaskar Dutta.

At least 217 records · Page 12Linked to original sources

arXiv2008

Determining the Dark Matter Relic Density in the Minimal Supergravity Stau-Neutralino Coannihilation Region at the Large Hadron Collider

We examine the stau-neutralino coannihilation (CA) mechanism of the early universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to the direct measurement by Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters m0, m1/2, A0 and tan(beta) without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and lighter stau masses in this CA region without assuming gaugino universality.

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arXiv2008

Large Phase of B_s-\bar B_s Mixing in Supersymmetric Grand Unified Theories

We consider the possibility of a large phase of B_s-\bar B_s mixing in supersymmetric SU(5) and SO(10) models. We find that in the SU(5) model, the magnitude of this phase is correlated with the branching ratio of τ-> μγand the phase can be within 2σof the recent UTfit analysis. In the case of SO(10) models, this correlation can be relaxed and a large phase can be obtained. In this scenario, a non-zero value of CP asymmetry for B -> X_sγwill be predicted. We predict the sparticle mass ranges for the LHC for these models once the UTfit result is accommodated and discuss the dark matter and the anomalous magnetic moment constraints on this analysis.

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arXiv2007

Proton Decay and Flavor Violating Thresholds in SO(10) Models

Discovery of neutrino mass has put the spotlight on supersymmetric SO(10) as a natural candidate for grand unification of forces and matter. However, the suppression of proton decay is a major problem in any supersymmetric grand unified models. In this paper we show how to alleviate this problem by simple threshold effect which raises the colored Higgsino masses and the grand unification scale to \gtrsim 10^{17} GeV. There exist only four types of fields arising from different SO(10) representations which can generate this kind of threshold effects. Some of these fields also generate a sizable flavor violation in the quark sector compared to the lepton sector. The b-τunification can work in these types of models even for intermediate values of tanβ.

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arXiv2007

Unifying inflation and dark matter with neutrino masses

We propose a simple model where a {\it gauge invariant inflaton} is responsible for cosmic inflation and generates the seed for structure formation, while its relic {\it thermal} abundance explains the missing matter of the universe in the form of cold dark matter. The inflaton self-coupling also explains the observed neutrino masses. All the virtues can be attained in a minimal extension of the Standard Model gauge group around the TeV scale. We can also unveil these properties of an inflaton in forthcoming space and ground based experiments.

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arXiv2007

Constraint from D - anti-D Mixing in Left-Right Symmetric Models

We study the constraint arising from the recently observed D - anti-D mixing in the context of supersymmetric models with left-right symmetry. In these models, the supersymmetric contributions in the mixing amplitudes of D - anti-D, K - anti-K and B - anti-B are all correlated. We compare the constraint from the D - anti-D mixing with the K - anti-K mixing and find that the D - anti-D mixing constrains the maximal supersymmetric contribution to the B_s - anti-B_s mixing amplitude. The maximal supersymmetric contribution can allow a large CP phase of B_s - anti-B_s mixing which agrees with the recent measurement of the CP asymmetry of B_s -> J/psi phi decay.

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arXiv2007

No-Scale Solution to Little Hierarchy

We show that the little hierarchy problem can be solved in the no-scale supergravity framework. In this model the supersymmetry breaking scale is generated when the electroweak symmetry breaking condition is satisfied and therefore, unlike usual supersymmetric models, the correlation between the electroweak symmetry breaking scale and the average stop mass scale can be justified. This correlation solves the little hierarchy puzzle. Using minimal supergravity boundary conditions, we find that the parameter space predicted by no-scale supergravity is allowed by all possible experimental constraints. The predicted values of supersymmetric particle masses are low enough to be very easily accessible at the LHC. This parameter space will also be probed in the upcoming results from the dark matter direct detection experiments.

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arXiv2007

An Inflationary Scenario in Intersecting Brane Models

We propose a new scenario for D-term inflation which appears quite straightforwardly in the open string sector of intersecting brane models. We take the inflaton to be a chiral field in a bifundamental representation of the hidden sector and we argue that a sufficiently flat potential can be brane engineered. This type of model generically predicts a near gaussian red spectrum with negligible tensor modes. We note that this model can very naturally generate a baryon asymmetry at the end of inflation via the recently proposed hidden sector baryogenesis mechanism. We also discuss the possibility that Majorana masses for the neutrinos can be simultaneously generated by the tachyon condensation which ends inflation. Our proposed scenario is viable for both high and low scale supersymmetry breaking.

hep-th↗

arXiv2007

Probing the parameter space for an MSSM inflation and the neutralino dark matter

The flat directions LLe and udd within the minimal supersymmetric Standard Model provide all the necessary ingredients for a successful inflation with the right amplitude of the scalar density perturbations, negligible gravity waves and the spectral tilt within 2σobserved range 0.92 \leq n_s \leq 1.0. In this paper we explore the available parameter space for inflation in conjunction with a thermal cold dark matter abundance within the minimal supergravity model. Remarkably for the inflaton, which is a combination of squarks and sleptons, there is a stau-neutralino coannihilation region below the inflaton mass 500 GeV for the observed density perturbations and the tilt of the spectrum. For such a low mass of the inflaton the LHC is capable of discovering the inflaton candidates within a short period of its operation. Inflation is also compatible with the focus point region which opens up for the inflaton masses above TeV. We show that embedding MSSM within SO(10) can naturally favor this region.

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arXiv2007

Landscape of Little Hierarchy

We investigate the little hierarchy between Z boson mass and the SUSY breaking scale in the context of landscape of electroweak symmetry breaking vacua. We consider the radiative symmetry breaking and found that the scale where the electroweak symmetry breaking conditions are satisfied and the average stop mass scale is preferred to be very close to each other in spite of the fact that their origins depend on different parameters of the model. If the electroweak symmetry breaking scale is fixed at about 1 TeV by the supersymmetry model parameters then the little hierarchy seems to be preferred among the electroweak symmetry breaking vacua. We characterize the little hierarchy by a probability function and the mSUGRA model is used as an example to show the 90% and 95% probability contours in the experimentally allowed region. We also investigate the size of the Higgsino mass by considering the distribution of electroweak symmetry breaking scale.

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arXiv2007

Cosmology and Dark Matter at the LHC

We examine the question of whether neutralinos produced at the LHC can be shown to be the particles making up the astronomically observed dark matter. If the WIMP alllowed region lies in the SUGRA coannihilation region, then a strong signal for this would be the unexpected near degeneracy of the stau and neutralino i.e., a mass difference ΔM\simeq (5-15) GeV. For the mSUGRA model we show such a small mass difference can be measured at the LHC using the signal 3τ+jet+E_T^{\rm miss}. Two observables, opposite sign minus like sign pairs and the peak of the ττmass distribution allows the simultaneous determination of ΔM to 15% and the gluino mass M_{\tilde g} to be 6% at the benchmark point of M_{\tilde g}=850 GeV, A_0=0, μ>0 with 30 fb^{-1}. With 10 fb^{-1}, ΔM can be determined to 22% and one can probe the parameter space up to m_{1/2}=700 GeV with 100 fb^{-1}.

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arXiv2006

Modification of the Unitarity Relation for sin2beta-Vub in Supersymmetric Models

Recently, a more than 2sigma discrepancy has been observed between the well measured inclusive value of Vub and the predicted value of Vub from the unitarity triangle fit using the world average value of sin2beta. We attempt to resolve this tension in the context of grand unified SO(10) and SU(5) models where the neutrino mixing matrix is responsible for flavor changing neutral current at the weak scale and the models with non-proportional A-terms (can be realized simply in the context of intersecting D-brane models) and investigate the interplay between the constraints arising from B_{s,d}-\bar B_{s,d} mixings, epsilon_K, Br(tau -> mu gamma), Br(mu -> e gamma) and a fit of this new discrepancy. We also show that the ongoing measurement of the phase of Bs mixing will be able to identify the grand unified model. The measurement of Br(tau -> e gamma) will also be able to test these scenarios, especially the models with non-proportional A-terms.

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arXiv2006

B(s)-B(s)bar Mixing in Supersymmetric Grand Unified Models

We study B_s-\bar{B}_s mixing in grand unified SO(10), SU(5) models where the mixings among the second and third generation squarks arise due to the existence of flavor violating sources in the Dirac and Majorana couplings which are responsible for neutrino mixings. We find that when the branching ratio of tau->mu gamma decay is enhanced to be around the current experimental bound, B_s-\bar{B}_s mixing may also contain large contribution from supersymmetry in the SO(10) boundary condition. Consequently, the phase of B_s-\bar{B}_s mixing is large (especially for small tan beta and large scalar mass m_0) and can be tested by measuring CP asymmetries of B_s decay modes.

hep-ph↗

arXiv2006

Hidden Sector Baryogenesis

We introduce a novel mechanism for baryogenesis, in which mixed anomalies between the hidden sector and $U(1)_{baryon}$ drive the baryon asymmetry. We demonstrate that this mechanism occurs quite naturally in intersecting-brane constructions of the Standard Model, and show that it solves some of the theoretical difficulties faced in matching baryogenesis to experimental bounds. We illustrate with a specific example model. We also discuss the possible signals at the LHC.

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arXiv2006

$B_s - \bar B_s$ Mixing and Its Implication for $b \to s$ Transitions in Supersymmetry

We investigate the effect of the current measurement of the neutral $B_s$ meson mass difference, $ΔM_{B_s}$, on SUGRA models which have non-zero values of the soft breaking terms $(m^2_{LL,RR})_{23}$ and $A^{u,d}_{23}$ at the GUT scale. We use non-zero values of these parameter to explain the $B\to Kπ$ puzzle and find that even after satisfying the experimental result on $ΔM_{B_s}$ and the branching ratio (BR) of $b\to sγ$ we still can explain the puzzle. Further we show that in this parameter space it is possible to accommodate the large BR of $B\to η' K$ and the current experimental data for CP asymmetries of $B\to η' K^0$ and $B\to ϕK^0$. The predicted value of $\sin (2β^{\rm eff})_{η' K^0}$ is about $0.52-0.67$.

hep-ph↗

arXiv2006

Lepton Flavor Violation in Intersecting D-brane Models

We investigate lepton flavor violation in the context of intersecting D-brane models. We point out that these models have a source to generate flavor violation in the trilinear scalar couplings while the geometry of the construction leads to degenerate soft scalar masses for different generations (as in the minimal supergravity model) at the string scale. The trilinear scalar couplings are not proportional to the Yukawa couplings when the F-term of the U-moduli contribution is non-zero. Consequently, the lepton flavor violating decay processes are generated. Only other sources of flavor violations in this model are the Dirac neutrino Yukawa coupling and the Majorana couplings. The observed fermion mixings are realized from the ``almost rank 1" Yukawa matrices, which generate a simple texture for the trilinear scalar terms. We calculate the branching ratios of tau -> mu gamma, mu -> e gamma and the electric dipole moment of the electron in this model. We find that the observation of all the lepton flavor violating decay processes and the electric dipole moment will be able to sort out different flavor violating sources.

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arXiv2006

Detection of SUSY in the Stau-Neutralino Coannihilation Region at the LHC

We study the feasibility of detecting the stau neutralino (stau_1-neutralino_1)coannihilation region at the LHC using tau leptons. The signal is characterized by multiple low energy tau leptons from neutralino_2-->tau stau_1-->tau tau neutralino_1 decays, where the stau_1 and neutralino_1 mass difference (Delta M) is constrained to be 5-15 GeV by current experimental bounds including the bound on the amount of neutralino cold dark matter. Within the framework of minimal supergravity models, we show that if hadronically decaying tau's can be identified with 50% efficiency for visible pt >20 GeV the observation of such signals is possible in the final state of two tau leptons plus large missing energy and two jets. With a gluino mass of 830 GeV the signal can be observed with as few as 3-10 fb^-1 of data (depending on the size of Delta M). Using a mass measurement of the tau pairs with 10 fb^-1 we can determine dM with a statistical uncertainty of 12% for Delta M = 10 GeV and an additional systematic uncertainty of 14% if the gluino mass has an uncertainty of 5%.

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arXiv2005

Properties of Fermion Mixings in Intersecting D-brane Models

We consider the Yukawa couplings for quarks and leptons in the context of Pati-Salam model using intersecting D-brane models where the Yukawa coupling matrices are rank one in a simple choice of family replication. The CKM mixings can be explained by perturbing the rank 1 matrix using higher order terms involving new Higgs fields available in the model. We show that the near bi-large neutrino mixing angles can be naturally explained, choosing the light neutrino mass matrix to be type II seesaw dominant. The predicted value of U_{e3} is in the range \simeq 0.05-0.15. In the quark sector, V_{cb} is naturally close to the strange/bottom quark mass ratio and we obtain an approximate relation V_{ub} V_{cb} \simeq (m_s/m_b)^2 V_{us}. The geometrical interpretations of the neutrino mixings are also discussed.

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arXiv2005

Observable Neutron Antineutron Oscillation in High Scale Seesaw Models

We discuss a realistic high scale ($v_{BL}\sim 10^{12}$ GeV) supersymmetric seesaw model based on the gauge group $SU(2)_L\times SU(2)_R\times SU(4)_c$ where neutron-anti-neutron oscillation can occur at an observable rate. This is contrary to the naive dimensional arguments which say that $τ_{N-\bar{N}}\propto v_{BL}^5$ and is therefore unobservable if the seesaw scale $v_{BL}\geq 10^{5}$ GeV. Two reasons for the enhanced rate in our model are: (i) accidental global symmetries which keep some of the diquark Higgs masses at the weak scale and (ii) a new supersymmetric contribution from a lower dimensional operator. The net result is that $τ_{N-\bar{N}}\propto v_{BL}^2 v^3_{wk}$ rather than $v^5_{BL}$, causing the enhancement. The model can also explain the origin of matter via leptogenesis and is testable at LHC where the light diquark states can be produced.

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