Achieving New Upper Bounds for the Hypergraph Duality Problem through Logic

The hypergraph duality problem DUAL is defined as follows: given two simple hypergraphs $\mathcal{G}$ and $\mathcal{H}$, decide whether $\mathcal{H}$ consists precisely of all minimal transversals of $\mathcal{G}$ (in which case we say that $\mathcal{G}$ is the dual of $\mathcal{H}$). This problem is equivalent to deciding whether two given non-redundant monotone DNFs are dual. It is known that non-DUAL, the complementary problem to DUAL, is in $\mathrm{GC}(\log^2 n,\mathrm{PTIME})$, where $\mathrm{GC}(f(n),\mathcal{C})$ denotes the complexity class of all problems that after a nondeterministic guess of $O(f(n))$ bits can be decided (checked) within complexity class $\mathcal{C}$. It was conjectured that non-DUAL is in $\mathrm{GC}(\log^2 n,\mathrm{LOGSPACE})$. In this paper we prove this conjecture and actually place the non-DUAL problem into the complexity class $\mathrm{GC}(\log^2 n,\mathrm{TC}^0)$ which is a subclass of $\mathrm{GC}(\log^2 n,\mathrm{LOGSPACE})$. We here refer to the logtime-uniform version of $\mathrm{TC}^0$, which corresponds to $\mathrm{FO(COUNT)}$, i.e., first order logic augmented by counting quantifiers. We achieve the latter bound in two steps. First, based on existing problem decomposition methods, we develop a new nondeterministic algorithm for non-DUAL that requires to guess $O(\log^2 n)$ bits. We then proceed by a logical analysis of this algorithm, allowing us to formulate its deterministic part in $\mathrm{FO(COUNT)}$. From this result, by the well known inclusion $\mathrm{TC}^0\subseteq\mathrm{LOGSPACE}$, it follows that DUAL belongs also to $\mathrm{DSPACE}[\log^2 n]$. Finally, by exploiting the principles on which the proposed nondeterministic algorithm is based, we devise a deterministic algorithm that, given two hypergraphs $\mathcal{G}$ and $\mathcal{H}$, computes in quadratic logspace a transversal of $\mathcal{G}$ missing in $\mathcal{H}$.Comment: Restructured the presentation in order to be the extended version of a paper that will shortly appear in SIAM Journal on Computin

h\to \gamma \gamma In Inert Higgs Doublet Model

Motivated by the recent result reported from LHC on the di-photon search for a Standard Model (SM) Higgs-like boson. We discuss the implications of this possible signal in the framework of the Inert Higgs Doublet Model (IHDM), taking into account previous limits from Higgs searches at LEP, the Tevatron and the LHC as well as constraints from unitarity, vacuum stability and electroweak precision tests. We show that the charged Higgs contributions can interfere constructively or destructively with the W gauge bosons loops leading to enhancement or suppression of the di-photon rate with respect to SM rate. We show also that the invisible decay of the Higgs, if open, could affect the total width of the SM Higgs boson and therefore suppress the di-photon rate.Comment: 15 pages, added reference

The Hard X-ray emission of the blazar PKS 2155--304

The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS 2155$-$304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10 keV) lies mostly in the falling part of the synchrotron hump. We aim to study the X-ray emission of PKS 2155$-$304 during different intensity states in 2009$-$2014 using XMM$-$Newton satellite. We studied the spectral curvature of all of the observations to provide crucial information on the energy distribution of the non-thermal particles. Most of the observations show curvature or deviation from a single power-law and can be well modeled by a log parabola model. In some of the observations, we find spectral flattening after 6 keV. In order to find the possible origin of the X-ray excess, we built the Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in PKS 2155--304 is difficult to fit in the one zone model but, could be easily reconciled in the spine/layer jet structure. The hard X-ray excess can be explained by the inverse Comptonization of the synchrotron photons (from the layer) by the spine electrons.Comment: 14 pages, 7 Figures, Accepted for publication in Ap

Multi-Band Intra-Night Optical Variability of BL Lacertae

We monitored BL Lacertae frequently during 2014 - 2016 when it was generally in a high state. We searched for intra-day variability for 43 nights using quasi-simultaneous measurements in the B, V, R, and I bands (totaling 143 light curves); the typical sampling interval was about eight minutes. On hour-like timescales, BL Lac exhibited significant variations during 13 nights in various optical bands. Significant spectral variations are seen during most of these nights such that the optical spectrum becomes bluer when brighter. The amplitude of variability is usually greater for longer observations but is lower when BL Lac is brighter. No evidence for periodicities or characteristic variability time-scales in the light curves was found. The color variations are mildly chromatic on long timescales.Comment: 15 pages, 5 Figures, 3 Tables; Accepted for publication in Galaxies; a special issue on Microvariability of Blazar

Double-lepton polarization asymmetries in the (B -> K l^+ l^-) decay beyond the Standard Model

General expressions for the double-lepton polarizations in the (B -> K l^+ l^-) decay are obtained, using model independent effective Hamiltonian, including all possible interactions. Correlations between the averaged double-lepton polarization asymmetries and the branching ratio, as well as, the averaged single-lepton polarization asymmetry are studied. It is observed that, study of the double-lepton polarization asymmetries can serve as a good test for establishing new physics beyond the Standard Model.Comment: 21 pages, 18 figures, LaTeX formatte

A gene producing one to nine flowers per flowering node in chickpea

Chickpea (Cicer arietinum L.) has a racemose type of inflorescence and at each axis of the raceme usually one or two and rarely three flowers are borne. Plants producing 3 to 9 flowers, arranged in a cymose inflorescence, at many axis of the raceme, were identified in F2 of an interspecific cross ICC 5783 (C. arietinum) × ICCW 9 (C. reticulatum) in which both the parents involved were single-flowered. A spontaneous mutation in one of the two parents or in the F1 was suspected. However, the possibility for establishment of a rare recombination of two interacting recessive genes could not be ruled out. The number of pods set varied from 0 to 5 in each cyme. Inheritance studies indicated that a single recessive gene, designated cym, is responsible for cymose inflorescence. The allelic relationship of cym with sfl, a gene for double-flowered trait, was studied from a cross involving multiflowered plants and the double-flowered line ICC 4929. The cym gene was not allelic to sfl, suggesting that two loci control the number of flowers per peduncle in chickpea. The cym locus segregated independently of the locus sfl, ifc (inhibitor of flower color) and blv (bronze leave)

Scale Inside-Out: Rapid Mitigation of Cloud DDoS Attacks

The distributed denial of service (DDoS) attacks in cloud computing requires quick absorption of attack data. DDoS attack mitigation is usually achieved by dynamically scaling the cloud resources so as to quickly identify the onslaught features to combat the attack. The resource scaling comes with an additional cost which may prove to be a huge disruptive cost in the cases of longer, sophisticated, and repetitive attacks. In this work, we address an important problem, whether the resource scaling during attack, always result in rapid DDoS mitigation? For this purpose, we conduct real-time DDoS attack experiments to study the attack absorption and attack mitigation for various target services in the presence of dynamic cloud resource scaling. We found that the activities such as attack absorption which provide timely attack data input to attack analytics, are adversely compromised by the heavy resource usage generated by the attack. We show that the operating system level local resource contention, if reduced during attacks, can expedite the overall attack mitigation. The attack mitigation would otherwise not be completed by the dynamic scaling of resources alone. We conceived a novel relation which terms “Resource Utilization Factor” for each incoming request as the major component in forming the resource contention. To overcome these issues, we propose a new “Scale Inside-out” approach which during attacks, reduces the “Resource Utilization Factor” to a minimal value for quick absorption of the attack. The proposed approach sacrifices victim service resources and provides those resources to mitigation service in addition to other co-located services to ensure resource availability during the attack. Experimental evaluation shows up to 95 percent reduction in total attack downtime of the victim service in addition to considerable improvement in attack detection time, service reporting time, and downtime of co-located services

Employing Program Semantics for Malware Detection

In recent years, malware has emerged as a critical security threat. Additionally, malware authors continue to embed numerous anti–detection features to evade existing malware detection approaches. Against this advanced class of malicious programs, dynamic behavior–based malware detection approaches outperform the traditional signature–based approaches by neutralizing the effects of obfuscation and morphing techniques. The majority of dynamic behavior detectors rely on system–calls to model the infection and propagation dynamics of malware. However, these approaches do not account an important anti–detection feature of modern malware, i.e., system–call injection attack. This attack allows the malicious binaries to inject irrelevant and independent system–calls during the program execution thus modifying the execution sequences defeating the existing system–call based detection. To address this problem, we propose an evasion–proof solution that is not vulnerable to system–call injection attacks. Our proposed approach precisely characterizes the program semantics using Asymptotic Equipartition Property (AEP) mainly applied in information theoretic domain. The AEP allows us to extract the information–rich call sequences that are further quantified to detect the malicious binaries. Furthermore, the proposed detection model is less vulnerable to call–injection attacks as the discriminating components are not directly visible to malware authors. This particular characteristic of proposed approach hampers a malware author’s aim of defeating our approach. We run a thorough set of experiments to evaluate our solution and compare it with existing system-call based malware detection techniques. The results demonstrate that the proposed solution is effective in identifying real malware instances

DDoS victim service containment to minimize the internal collateral damages in cloud computing

Recent Distributed Denial of Service (DDoS) attacks on cloud services demonstrate new attack effects, including collateral and economic losses. In this work, we show that DDoS mitigation methods may not provide the expected timely mitigation due to the heavy resource outage created by the attacks. We observe an important Operating System (OS) level internal collateral damage, in which the other critical services are also affected. We formulate the DDoS mitigation problem as an OS level resource management problem. We argue that providing extra resources to the victim's server is only helpful if we can ensure the availability of other services. To achieve these goals, we propose a novel resource containment approach to enforce the victim's resource limits. Our real-time experimental evaluations show that the proposed approach results in reduction in the attack reporting time and victim service downtime by providing isolated and timely resources to ensure availability of other critical services